SCIENCE FOR SOUTH AFRICA
VOLUME 2 • NUMBER 2 • 2005 R20 incl. VAT
ACADEMY OF SCIENCE OF SOUTH AFRICA
SALT “gigantic African eye”
David Buckley How the largest single optical telescope in the southern hemisphere was built 16
Observing the Universe
Astronomers from the SAAO and the University of Cape Town Revelations from spectacular skies over southern Africa The distance scale of the Universe, Michael Feast • Light echoes reveal the structure of interstellar space, Lisa Crause • Borderline between neutron stars and black holes, Phil Charles • Eta Carinae: the next Galactic supernova? Patricia Whitelock • Clusters and superclusters of galaxies, Patrick Woudt • First science with SALT, Darragh O’Donoghue 30
Contents VOLUME 2 • NUMBER 2 • 2005
Views from space: Earth observation 35
Satellites and the electromagnetic spectrum
From dust to dust: a cosmic quest Massive clouds of tiny, icy grains in interstellar space
David Laney 36
Traditions from southern Africa
Finding the nearest star
Ian Glass It happened in South Africa a century ago
New era for southern African astronomy
Fact file SALT: empowering facts More about SALT • A day in the life of SALT • Astronomy to empower the country Science news A South African first for TB research • Lessons from cyclones (p.15)
Careers In astronomy, the sky’s the limit!
Your QUESTions answered Hurricanes – Ian Meiklejohn
Viewpoint Interview On project management Kobus Meiring
The S&T tourist Gateways to the Universe Visit planetariums – and Sutherland too
Letters to QUEST
Diary of events
Books Books Africa’s Giant Eye: Building the Southern African Large Telescope • and other titles
Subscription form • Back page science
Through SALT to a bright future
What is happening to the Earth’s magnetic field?
Peter Sutcliffe and Pieter Kotzé Space weather, auroras, and the Earth’s magnetic shield
The energetic Universe in gamma rays
Okkie de Jager Supernovas, cosmic rays, and new shapes in the Milky Way
Planning the Karoo Array Telescope
Kim de Boer Bold new project for radio astronomy
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Most ancient science racking the stars is a human impulse as old as civilization itself – and astronomy has always kept in line with the most advanced mathematical and technological skills available. In this International Year of Physics, South Africa inaugurates its new, world-class Southern African Large Telescope (SALT) in the cold, clear Karoo. This event celebrates the latest episode in a very long story of science on the move. People observing the stars have always recorded what they saw and applied their researches. Astronomy was at the very heart of trade as travellers and ships used the skies to navigate across deserts and oceans. Ancient Babylonian astronomy helped to tell the time and specify dates; the ancient Egyptians devised the first solar calendar, which fixed the length of the year at 365 days. This issue of QUEST is an update, describing some of the latest, remarkable, and most proudly South African achievements in exploring the Universe. SALT, a triumph of engineering and design (p. 16), in its prime viewing location, marks the start of a new era in the region’s astronomy (p. 3). Through it, the world’s astronomers will study what’s on offer in our southern skies – the Galactic Centre of the Milky Way; its neighbours, the Small and Large Magellanic Clouds; and countless other objects. In these pages, South African astronomers share their discoveries about black holes, galaxies, stars, and cosmic dust (p. 16 and p. 35). Year by year, our infrastructure is expanding to create an indispensable astronomical hub for the research that, for many reasons, is best done in the southern hemisphere. Apart from SALT, there’s ground-breaking research from HESS, the world’s most powerful very-high-energy gamma-ray telescope system near Windhoek (p. 25), and a new future for radio astronomy with the planned Karoo Array Telescope (p. 28). The Hermanus Magnetic Observatory has investigated the Earth’s magnetic field (p. 22) – when’s a reversal due? – and, in very practical ways, satellite observations of Earth monitor events such as fires (p. 30) and tropical cyclones (p. 32) and help, perhaps, to protect people against the worst effects. Since time began, the cosmos has gripped the human imagination everywhere including southern Africa – giving rise to starlore (p. 39) and a history of curiosity satisfied (p. 36). Large parts of South Africa still enjoy stunning views of the night sky, now denied to much of Western Europe and the USA, polluted as theirs is by light from crowded cities. Those who grow up and live in southern Africa have precious opportunities to appreciate these skies, learn from them, and draw inspiration from them, for generations to come.
Cross section of the Southern African Large Telescope. In the background, SALT ‘first light’ picture of the Lagoon Nebula (central regions). Pictures courtesy of the SAAO/SALT Foundation SCIENCE FOR SOUTH AFRICA
Editor Elisabeth Lickindorf Editorial Board Wieland Gevers (University of Cape Town) (Chair) Graham Baker (South African Journal of Science) Anusuya Chinsamy-Turan (University of Cape Town) George Ellis (University of Cape Town) Jonathan Jansen (University of Pretoria) Colin Johnson (Rhodes University) Correspondence and The Editor enquiries PO Box 1011, Melville 2109 South Africa Tel./fax: (011) 673 3683 e-mail: email@example.com (For more information visit www.assaf.co.za) Business Manager Neville Pritchard Advertising and Neville Pritchard subscription enquiries PO Box 130614 Bryanston 2074 South Africa Tel.: (011) 781 8388 Fax: (011) 673 3683 Cell: 083 408 3286 e-mail: firstname.lastname@example.org Copyright © 2005 Academy of Science of South Africa Published by the Academy of Science of South Africa (ASSAf) PO Box 72135, Lynnwood Ridge 0040, South Africa (011) 673 3683 Permissions Fax: e-mail: email@example.com (011) 781 8388 Back issues Tel.: Fax: (011) 673 3683 e-mail: firstname.lastname@example.org Subscription rates (4 issues and postage) (For subscription form, other countries, see p.48.)
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Elisabeth Lickindorf Editor – QUEST: Science for South Africa Join QUEST’s knowledge sharing activities ■
Write letters for our regular Letters column – e-mail or fax your letter to The Editor and win a prize. (Write QUEST LETTER in the subject line.) ■ Ask science and technology (S&T) questions for specialist members of the Academy of Science to answer in our regular S&T Questions and Answers column – e-mail or fax your questions to The Editor and win a prize. (Write S&T QUESTION in the subject line.) ■ Inform readers in our regular Diary of Events column about S&T events that you may be organizing. (Write QUEST DIARY clearly on your e-mail or fax and provide full and accurate details.) ■ Contribute if you are a specialist with research to report. Ask the Editor for a copy of QUEST’s Call for Contributions (or find it at www.assaf.co.za), and make arrangements to tell us your story. To contact the Editor, send an e-mail to: email@example.com or fax your communication to (011) 673 3683. Please give your full name and contact details.
emarkably, only two countries in the southern hemisphere pursue optical/infrared astronomy with very large telescopes – South Africa and Chile. Why just these? The answer, like the three top selling points for a private house, is location, location, location. Astronomers need clear skies, good seeing conditions (which, for the best star images, means a steady atmosphere), and uniform coverage of both summer and winter skies. Such requirements are met only by Chile and South Africa in the southern hemisphere. Australia cannot accommodate the very largest telescopes because it does not have the high mountains for the clear air needed. Parts of Antarctica are potentially superb for observation – but the cost of operating there is literally astronomical!
A novel telescope
South Africa’s rich astronomical history dates from the early 19th century when navigation and star catalogues were of prime importance. A relic of those times is the Noon Gun – still firing today in Cape Town from signals generated at the South African Astronomical Observatory (SAAO) – according to which navigators used to set their chronometers before going out to sea. Such activities laid the foundations for astronomical institutes in Cape Town, Pretoria, and Johannesburg. In the 1970s, these merged to form the SAAO with its headquarters in Cape Town (in the original Royal Observatory buildings) and its research telescopes located in the high, dark Karoo near Sutherland. Although equipped with top quality and, in some cases, unique light detectors, these telescopes were never the largest in the world and, by the 1990s, had begun moving well down the international league table (based on size) of astronomical telescopes. How could South Africa compete with the multi-billion rand behemoths being constructed for US and European astronomers, such as Keck, Gemini, and the Very Large Telescope (VLT)? An answer came in the 1990s with the construction, for only 20% of the cost of the giants, of the pioneering 10-m-class Hobby-Eberly Telescope (HET) by astronomers at the University of Texas at Austin. They were keen to be involved in a southern hemisphere equivalent, and the revolutionary, affordable HET approach to building very large telescopes (see p. 7 ) meshed well with the aims and ideals of the established SAAO facilities, already widely known for their cost-effective research and instrumentation capabilities. The post-1994 South African government’s bold, new vision to stimulate broader interest and involvement in science combined with the driving force of my predecessor at SAAO, the late Dr Bob Stobie, to conceive the Southern African Large Telescope (SALT) project. SALT’s inauguration by President Thabo Mbeki on 10 November 2005 ushers in a new dawn for southern African astronomy.
Phil Charles explains what the Southern African Large Telescope means for our region. Quest 2(2) 2 0 0 5 3
SALT is special SALT’s observing time is shared among its 11 partners. South Africa, however, as the largest single partner, has almost 40% of the time, and now expects to become a major player in large telescope astronomy. We aim to exploit SALT’s unique capabilities compared to other very large telescopes, in particular: ■ high sensitivity in the blue part of the spectrum ■ high time resolution (with a capability of at least 100 milliseconds), enabling rapid variations to be seen (for instance, in accreting matter onto white dwarfs, neutron stars, and black holes) ■ queue scheduling of all observations (see p. 13). These explorations open up entirely new avenues of astronomical research, and act as an inspiration for scientific and technological development in South Africa.
The bigger picture In parallel with SALT, our neighbour, Namibia, hosts the world’s most sensitive high-energy gamma-ray telescope, the High Energy Stereoscopic System (HESS) near Windhoek (see p. 25). And, driven by the success of the multinational SALT project, South Africa has put in a bid for hosting the Square Kilometre Array (SKA) at a site based in the Karoo. (This is the most ambitious project ever contemplated in radio astronomy, with, literally, a square kilometre of antenna collecting area and dishes spread over distances as great as 2 000 km.) Work has begun on the Karoo Array Telescope (KAT), a South African ‘technology demonstrator’ version of SKA (see p. 25). These projects demonstrate the radical way in which three technologies have combined to change the nature of modern science, particularly astronomy, over the last 20–30 years. The advent of electronic imaging detectors in the 1980s (that is, the charge-coupled devices, or CCDs, used in modern digital photography) provided a dramatic gain of more than a factor of 10 in sensitivity over the older photographic plates. At the same time, following Moore’s Law of Computing (which describes a doubling in CPU complexity and memory capacity every two years!) we have seen a staggering increase in computing power per dollar, which has made it possible to simulate the physical processes occurring, for example, in the early Universe and supernova explosions. Furthermore, the exponential growth in Internet bandwidth has allowed extraordinary ease of communication and rapid transfer of information around the world. Together, these developments brought unprecedented advances in astrophysics – although many of the bandwidth gains are still to come in South Africa, as a result of outdated costing strategies still pursued by the state’s monopolistic telecommunications supplier. The improved efficiency of light detection brought about by CCDs – almost overnight – was so great that it was equivalent to doubling or tripling the mirror diameter of existing telescopes; telescope sizes themselves have also doubled and tripled, compounding the effect even further.
SALT, HESS, and KAT cover vastly different wavelength ranges, from ultra-high-energy gamma rays (the most powerful photons of all) to the visible light of everyday experience (a strength at Sutherland) to the region of radio waves (where Gauteng’s Hartebeesthoek Radio Astronomy Observatory traditionally has expertise). The recent development of multi-wavelength astronomy (born initially out of space astrophysics), which combines the different observations, allows for completely new understanding of ‘extreme’ objects, such as ■ very high density compact objects (white dwarfs, neutron stars, black holes), by probing the very nature of matter itself ■ supermassive black holes in the centre of active galaxies, the most powerful objects in the Universe, to provide access to the details of the large-scale structure of the Universe, taking us back towards the beginning of time ■ ultra-high magnetic field strengths that can lead to relativistic acceleration of particles, permitting tests of general relativity, which brings us to the ‘frontiers’ of modern physics. Data from SALT, HESS, and KAT are planned to be distributed to observers via the Internet. This method exploits the capabilities of the internationally agreed Astrophysical Virtual Observatory, whereby scientists anywhere in the world can access observational data without the time or expense of long-distance travel. Indeed, by combining our datasets with those of other observatories, the research potential could grow exponentially. All these multinational projects have significant South African direct involvement, with both SALT and KAT being led by scientists within this country. Modern large telescopes function for decades, not years, so these projects also demonstrate international confidence in the future stability of southern Africa.
International role model SALT was conceived in 1998; the ground-breaking ceremony at Sutherland took place in 2000. Building began in 2001, the 10-m-class telescope was essentially completed by mid-2005 (on truly breathtaking schedule and close to the original budget of about US$20 million), and ‘first light’ pictures appeared two months later. This remarkable achievement, with its particularly successful project management approach (see p. 40), has become a benchmark for future astronomical projects of this scale, Designers planning even larger facilities now look to SALT as role model for building affordable ‘extremely large telescopes’ of 30-, 50-, perhaps even 100-m diameter. In so many different ways, southern Africa is now, once again, at the forefront of astronomical technology and research. ■
At the South African Astronomical Observatory field station, Sutherland. Above: Karoo landscape around SALT. Middle: Domes housing the research telescopes. Below: SALT in the snow. Pictures courtesy of the SAAO/SALT Foundation
Professor Charles is Director of the SAAO and has enjoyed a 33-year career in High Energy Astrophysics, observing X-ray sources (particularly those involving neutron stars and black holes) both with space observatories and the largest telescopes around the world.
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David Buckley explains what’s unique and pioneering about what President Thabo Mbeki called “a gigantic African eye” – the largest single optical telescope in the southern hemisphere.
Photograph courtesy of Janus Brink
he newly completed Southern African Large Telescope (SALT) is at the field station of the South African Astronomical Observatory (SAAO), near Sutherland, in the south-west of the semi-arid, fossil-rich Karoo, in a small corner known as the Karoo Highlands or Roggeveld. With only two other towns – Williston to the north and Fraserburg in the north-east – the area is known for its sheep farming, and its cold, clear, dark nights. It is a good place for observing the night sky because, being sparsely populated, it has very little light pollution. Also, its position high on an isolated plateau (15 km east of Sutherland) means there is little atmospheric pollution. It is seldom overcast there because of the semi-desert location, and the nights are typically ‘cold and clear’. Furthermore, Sutherland is situated near the boundary of the two major weather systems in South Africa, which, respectively, have their rainy seasons in winter (the Cape) and summer (the north-east). This means it has a 75% chance of clear skies all year round. On a practical level, it is relatively near the conveniences of a large city – only 390 km (about 4 hours’ drive) from Cape Town. The southern hemisphere has surprisingly few places with such excellent conditions for
T High-level support “Now, in the small town of Sutherland in the semi-desert Karoo region of our country, we are building a gigantic African eye through which we can view the Universe. The construction of the single largest telescope in the southern hemisphere – SALT as it is called – will mean that in this humble home of the earliest humans, we are also building a vast gateway through which we can observe our earliest stars, learn about the formation of our Galaxy and the lives of other worlds so as to give us insights into our future. We are proud that SALT will not only enable southern African scientists to undertake important research, but also provide significant opportunities for international collaboration and scientific partnerships with the rest of the world.” President Thabo Mbeki at the opening of the South African Pavilion at Expo 2000, Hanover, Germany, 2 June 2000.
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observing the Universe. (The best are in Chile.) Up above, the Sun with its Solar System rotates in a 250-million-year orbit around our Galaxy, the Milky Way – some two-thirds of the way out from the Galactic Centre – having followed this path some 20 times in its 5-billion-year lifetime. Viewed from Earth, the centre of the Milky Way (in the direction of the constellation Sagittarius) appears overhead during the southern hemisphere winter as a diffuse band of light filled with stars and clouds (both dark and bright) of interstellar gas and dust. From our part of the world we have not only a glorious view of the Galactic Centre (which we now know contains a several-million-solar-mass black hole) but, more important, almost continuous viewing of both the Large and Small Magellanic Clouds, the nearest satellite galaxies to the Milky Way (some 180 000 and 210 000 light years away, respectively). Valuable in a wide variety of astronomical studies, these cannot be seen from northern hemisphere observatories but only from the southern hemisphere.
The origins of SALT As South African cities grew, light pollution increased (as it did around the world), making it
1. Different-sized telescopes are very useful to astronomers. Broadly speaking, the larger and more powerful a telescope, the more expensive it is. Some observation projects require very powerful telescopes (that is, large or many mirrors for light-gathering and recording) but, depending on the type of research the astronomer is conducting, many projects can be undertaken perfectly adequately with smaller telescopes. So all observatories have a range of telescope sizes, giving time for people to use the instruments they need without trying to undertake all their research with the large telescopes only. This makes much more efficient use of telescope time, with each telescope’s capabilities being fully exploited. Another reason for different kinds of telescope is that not all astronomy takes place at visible wavelengths, and different instruments are needed for observing different parts of the spectrum. One of the SAAO telescopes in Sutherland, for example, works only in the infrared (that is, at wavelengths longer than those visible to the naked eye). SALT, on the other hand, works mostly in the visible but extends into the ultraviolet (at wavelengths shorter than the visible part of the spectrum). The images produced are colour-enhanced, as a result of combining separate SALT exposures taken through different colour filters. Different-sized telescopes and many different instruments enable astronomers to look at whatever they need to observe. Not all astronomy is about looking further than ever before, so smaller telescopes remain in demand and perform a valuable service in supporting SALT.
impossible to operate front-rank astronomical facilities near major population centres. So, in 1972, to take advantage of Sutherland’s far superior observing conditions, the newly-formed SAAO moved its major telescopes there, including Pretoria’s 30-year-old 1.9-m Radcliffe reflector (designed and built in the 1940s) and Cape Town’s 1.0-m Elizabeth telescope. These were joined by two smaller telescopes1, and the SAAO began Sutherland operations in 1974. South Africa’s claim to having the largest optical telescope in the southern hemisphere (the 1.9-m Radcliffe reflector) ended in 1974, with the opening of the 3.9-m Anglo-Australian Telescope in New South Wales, Australia, soon to be followed by similar-sized telescopes in Chile. Consequently, by the 1990s, South African astronomers were finding it more and more difficult to compete with others elsewhere who, for the most part, had access to these larger and more powerful telescopes in the 4-m class2. The fact that South Africa was able to remain competitive with just a few 1- or 2-m-class telescopes was partly because of the good observing conditions at Sutherland and the relatively small size of the astronomical community, which gave its members regular and frequent access to the equipment. There was no doubt, however, that, to contribute meaningfully to ongoing advances in international astronomy, South Africa needed to improve and add to its facilities. When Bob Stobie became director of the SAAO in 1992, the Observatory had already decided in principle to build a modern 3.5-m telescope. It would be called the South African Large Telescope, and be similar in size and instrument design to others then being built in Chile and in the US (in Arizona)3. As the planning evolved, however, SALT developed into a far more extraordinary and pioneering venture.
Value for money
Pictures courtesy of SAAO/SALT Foundation (unless otherwise specified)
for them to be able to operate as if they were a single, large mirror – no easy task, as the alignment needs to be controlled to an accuracy of 100 nanometres (about 1/5 the wavelength of visible light), and for hours at a time. Keeping the altitude (or tilt) of the mirror at a specific angle also saved money. Telescopes are normally manipulated both in altitude (up and down) and azimuth (left to right) – that is, they traditionally swivel in all directions to view any object currently accessible anywhere in the sky. However, this comes at a huge engineering cost. So having a fixed tilt made the HET (and, subsequently, SALT) much cheaper to construct, and there was relatively little loss in terms of sky access (see pictures). Put another way, with this design the sky rotates around the telescope rather than the telescope having to track the heavens. To observe certain objects, an astronomer simply waits until the Earth’s rotation EAST moves them high enough in Eq the sky for the telescope to uat or see them. Using this technique, in the case of SALT, as much as 70% of the southern sky is observable at some time or other, and at any specific moment the telescope’s ‘window of opportunity’ covers about 12% of the observable sky. (It is not worth looking very near the horizon, for instance, where there is severe atmospheric ‘extinction’ of light4.) The ‘cost versus sky access’ trade-off offered ▲ ▲
Opportunity knocked when the McDonald Observatory in west Texas constructed the HobbyEberly Telescope (HET), which was inaugurated in 1997. It represented a major paradigm shift in large telescope design, in that this 10-m-class telescope was constructed at one fifth of the cost of a conventional telescope – in other words, it cost about the same as the far smaller 3.5-m telescope initially planned for SALT, which was to cost an estimated R90 million. The huge saving was made possible by the HET’s innovative mirror design and by the constraint on its angle of tilt. The HET was revolutionary in that it did not have a single large, and therefore expensive, mirror, but a far cheaper array of 91 small (1-m), identical mirrors, with spherical surfaces, combining to create one mirror surface. All that was needed was to align them precisely enough
Left: Why is SALT tilted at an angle of 37 degrees from the zenith? The HET tilt angle of 35 degrees was chosen as the optimum balance between accessing as much of the sky as possible (making this angle larger means pointing more towards the horizon, but at the cost of severe atmospheric extinction of the starlight) and minimizing atmospheric extinction (which is least when pointing directly up towards the zenith, but at the cost of viewing only a tiny fraction of the sky). The reason that SALT is tilted at 37 degrees from the zenith, however, is our unique access in the southern hemisphere to the Magellanic Clouds. Extending the tilt to 37 degrees allows us to access all parts of both Clouds (in particular, the Small Magellanic Cloud).
2. A 4-m class telescope has a mirror diameter in the region of 4 m; it includes telescopes whose mirror diameters range from 3.5 to 4.2 m. 3. The telescopes being built were the NTT (New Technology Telescope) of the European Southern Observatory (ESO) in Chile; the WIYN Telescope (named after the four partners, namely Wisconsin, Indiana, and Yale universities, and the National Optical Astronomy Observatories consortium) at Kitt Peak Observatory in Arizona, USA. 4. At the horizon we look through a much thicker ‘slice’ of atmosphere so less light passes through it. This is why we can look at sunsets without hurting our eyes, for example. Also there is more dust as we look through a lot of atmosphere closer to the ground, which is why the setting Sun appears so red, due to the scattering of the blue light.
NORTH POLE Direction of Earth’s rotation Above: This diagram of the globe shows SALT’s possible sky access – the only areas SALT cannot see are shaded. The telescope can be pointed in any left–right direction and, as the sky passes overhead, a significant viewing area unfolds.
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SALT’s timing The suggestion to build SALT came in 1998, as South Africa emerged from isolation. It was an opportunity to catch up in the field of astronomy, and to stimulate broader interest in science and technology. The new ANC government’s White Paper on Science and Technology: Preparing for the 21st Century (1996) explicitly supported astronomy, and with government backing, the SAAO had a real chance of launching the project and raising further international funding. The motivation was compelling. ■ South Africa’s astronomers and astrophysicists were internationally well regarded. ■ The Sutherland field station was a good observing site. ■ SALT would be an affordable 10-m class telescope in which relatively small-scale partners, such as individual university departments, could participate, with generous amounts of observing time. Synergies were also possible with other existing facilities. ■ SALT was not competing directly with other large telescopes (which emphasize the red to infrared region of the electromagnetic spectrum) nor would it attempt high spatial resolution imaging. It would concentrate instead on the relatively neglected shorter wavelengths, to the ultraviolet cut-off determined by the Earth’s ozone layer, together with time resolved studies, for which South African astronomers were already known. These shorter wavelengths need appropriately designed instruments. The telescope itself collects all the light that passes through the Earth’s atmosphere, but the instrumentation determines what is detected and measured or imaged. (High-performance short-wavelength instruments are more difficult and expensive to construct.) ■ SALT’s complex queue-scheduling allows for time domain studies of objects (that is, looking at how things change over timescales of days, months, or years), and builds on South African pioneering work in high time resolution astronomy: looking at objects that vary on very short timescales of seconds or less. Queue-scheduling differentiates SALT from almost all other major telescope facilities and turns the viewing angle constraint into a scientific advantage. ■ The proposal for the 10-m SALT – renamed the Southern African Large Telescope to reflect its regional importance – immediately won support from Khotso Mokhele (President of what is now the National Research Foundation), Rob Adam (of the Department of Arts, Culture, Science & Technology and later its Director-General), Minister Ben Ngubane, and the full cabinet. In the 1998 budget vote, R50 million was earmarked for SALT, as long as a similar total contribution was secured from partner institutions. (The necessary funding was provided by the USA, Poland, Germany, New Zealand, and the UK.) Many people helped to design SALT, including the SALT team, SAAO technical staff and astronomers, specialist instrument designers, and engineers and scientists from other telescopes, in particular Keck (in Hawaii) and HET. The project took five and a half years to complete, nearly three years less than any comparable project to date. The ground-breaking ceremony took place on 1 September 2000, and, exactly five years later, on 1 September 2005, ‘first light’ pictures were officially released (see www.saao.ac.za/news/salt_light.html).
Far right: Primary mirror segment number 5 before being aluminized. Right: Unlike conventional telescopes, SALT’s primary mirror (composed of hexagonal segments, below) remains stationary as it collects starlight during observation. The only movement is from the tracker (the dark structure, above), which carries instruments on the prime focus payload and migrates across the primary mirror.
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astronomers a very good deal. In addition, instead of the massive telescope tube structure moving to track an object as the Earth rotates, the tracking in both HET and SALT is done by moving a much smaller ‘payload’ of instruments on a ‘tracker’ across the focal plane of the telescope (called the Prime Focus)5. The fact that the tracker, although a very complex and expensive item, was the only part of the telescope that needed to move to follow an object also kept costs down. The South Africans were delighted at the suggestion of using the HET as a model for the new, improved SALT. Suddenly the plan had changed. No longer would they have a 4-m class telescope but a far more powerful 10-m class one for the same price6, as the cost of manufacturing 91 identical spherical mirrors and aligning them is far less than manufacturing a single surface of the same area. SALT would now be the largest single optical telescope in the southern hemisphere and equal to the largest in the world.
Trailblazing design The SALT Project Team used the HET concept as a template. They were able to improve the design by benefiting from the HET experience and from the technological advances since its completion in 1997. The primary mirror of each of these telescopes is stationary, with an array of 91 identical hexagonal mirror segments, each with a spherical surface. Although the single large mirror in conventional telescopes is easier to use, the cost of building one this size would be prohibitive and technically difficult to produce. (In fact, the largest casting furnaces currently available can produce mirrors no greater than 8 m in diameter.) A mirror composed of segments is no less efficient than a single one, provided the segments are properly aligned. A major area of improvement in the SALT design was in the alignment system of its primary mirror segments. Some 480 capacitative edge sensors were added to measure the mirror segments’ relative movements and then to correct for this motion by moving 273 ‘actuators’ (that is, small motors at the back of the mirrors that can 5. The SALT tracker is used as follows. When an astronomer wishes to observe an object (for example, a star, galaxy, cluster, or nebula) as it moves through the field of view of SALT, the tracker’s job is to move with the image of the object produced by the telescope and make sure that its light is constantly focused onto the instrumentation that produces an image or spectrum. During the ‘track’, the main telescope structure stays fixed in position and does not need to move (which contributes to SALT’s stability and resistance to wind-shake), because only the tracker moves when a given object is being observed. 6. SALT is known as a 10-m class telescope. It can be awkward to define telescope size precisely when some telescope mirrors (such as SALT’s) are no longer the traditionally circular kind. SALT’s mirror is hexagonal (because of the hexagonal shape of the segments) so its dimensions are technically close to 10 m 11 m. In addition, because of moving the tracker, the telescope’s effective mirror size changes during an observation.
tip, tilt, and piston the mirrors) – three per mirror7. Such precise positioning of the mirrors allows the 91 individual mirrors to behave optically as if they were a single, huge 10-m surface. In terms of the overall performance of the telescope, the most significant improvement in SALT was the redesign of the ‘spherical aberration corrector’ (SAC). The SAC is needed to correct for the inherent optical aberration (known as ‘spherical aberration’) that arises from using a spherical mirror8, as without it the images would be uselessly blurry. SALT’s pioneering SAC, designed by SAAO astronomer Darragh O’Donoghue, makes this telescope able to deliver high-quality images. Special new coatings give it the ability to look much further into the ultraviolet and blue regions of the spectrum than most other optical telescopes9. In addition, the new SAC design quadrupled the area of sky visible in individual SALT images (compared with HET) to a respectable 8-arc minute (arcmin) diameter field
of view for the telescope – about a quarter the size of the full Moon10 – and made it possible to use the full primary mirror array of SALT (HET is limited to a maximum of about 9 m). Finally, the new SAC has a more compact design, allowing larger and more capable instruments than the HET’s to be housed on the Prime Focus Tracker – these are essential for fully exploiting SALT’s improved efficiency in the UV-blue region. Today SALT is one of a handful of large telescopes operating in the southern hemisphere11. The Very Large Telescope (VLT) was built and is run by the European Southern Observatory on Cerro Paranal in Chile. It has four 8-m telescopes that can work together and function as a single telescope equivalent to 16 m in diameter – when they do, this is the largest in
Prime focus payload Rotating structure Prime focus imaging spectrograph
SALTICAM (SALT Imaging Camera) Slit viewer mirrors
SALTICAM electronics, guidance camera, and controllers Light from primary mirror
Spherical aberration corrector (SAC) Calibration system
The SALT Partnership SALT is a truly international effort. Apart from South Africa’s National Research Foundation – the single largest partner – there are ten others in the SALT consortium including: Poland, five universities from the USA (Wisconsin, Rutgers, Dartmouth, Carnegie Mellon and North Carolina), the HET Board, the UK consortium (comprising the Armagh Observatory and Central Lancashire, Keele, Nottingham, Southampton, and Open universities), one university in Germany (Göttingen), and one in New Zealand (Canterbury).
the world. Most of the time, however, the VLT telescopes operate individually, which is why SALT, at 10 m, is the largest single optical telescope in the southern hemisphere. ■ Dr Buckley of the SAAO is SALT Project Scientist and Astronomy Operations Manager. He has extensive observational experience and he also has an interest in SAAO instrumentation. (Additional editorial contributions from Lisl Robertson and Phil Charles.)
7. The size of each sensor, which is basically a thin copper strip glued to the edge of the mirror, is about 15 cm 4 cm, and each actuator is about 10 cm 1 cm (these are little motors attached to lever arms that support the mirrors). 8. Parabolic mirrors and spherical mirrors, both curved, work optically in very different ways because of their different focusing properties. Most telescopes use parabolic mirrors, but the major cost-saving innovation in SALT and HET was to use many identical spherical mirrors. A parabolic mirror is shaped like part of a cone (like the shape you get when you cut a rugby ball in half); a spherical mirror is shaped more like half a soccer ball and, because the curve is the same all over the surface, allows 91 identical mirrors to act together as one surface. 9. The new SAC design allows SALT to obtain much sharper images than HET, over a larger field of view, and using more of the primary mirror area. Ultraviolet (UV) is shortward of the blue end of the visible spectrum, a region largely ignored by other large telescopes (which concentrate on the infrared region of the spectrum so as to observe distant, very faint objects). SALT’s unique capability in the blue is ideal for observing very energetic, hot stars, as well as high-energy phenomena (such as stellar and supermassive black holes), which are very active in the UV and X-ray part of the spectrum. To exploit SALT’s greater capability fully, appropriate instruments are needed. The wider the wavelength range over which the instruments operate, the larger and more complex they need to be, and that is certainly true of the prime focus imaging spectrograph (now renamed the Robert Stobie Spectrograph). 10. The 8-arcmin field of view represents SALT’s ‘footprint’ on the sky, that is, what it can see at any one time. As for geographical latitude locations on Earth, the celestial sphere is divided into degrees, with 60 arcmin in a degree, so 8 arcmin on the celestial sphere (imagine the sky as a huge sphere surrounding Earth) translates to the size of about a quarter of the full Moon. This is how much SALT has in view when pointed at any point on the sky. 11. A ‘large telescope’ is a relative term. In current usage, it refers to a telescope with a diameter of 8 m or more, of which there are five in the southern hemisphere. The world’s major telescopes are listed at www.absoluteastronomy.com/encyclopedia/l/li/list_of_largest_optical_reflecting_telescopes
Above left: SALT mirror support structure. The (purple-red) steel structure provides the rigid main support for the telescope in which the (blue) truss containing each mirror segment sits. The (pen-like) silvertopped cylinders protruding into the truss are the actuator motors, which control the exact positioning of each mirror segment. Above middle: SALT primary mirror during construction, reflecting the dome lights and other parts of the structure. Photographs courtesy of Phil Charles
Above right: The completed primary mirror pf SALT before the cleaning and re-aluminizing of all the segments.
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28-m mirror segment alignment tower (CCAS)
Tracker and prime focus payload 26-m-diameter dome
Telescope structure 11-m primary mirror array and truss Telescope building
Mirror-coating room Spectrometer room
Computer room, housing the telescope control system
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Pictures courtesy of SAAO/Salt Foundation
Q Fact file More about SALT ■ Design: modified version of the HobbyEberly Telescope (HET) at the McDonald Observatory in Texas, USA. ■ Telescope: length 13 m; mass 100 tonnes; 91-segment primary mirror array with a total hexagonal area of 11.1 m 9.8 m and a light collecting area of 77.2 m2. ■ Wavelength coverage: 320–900 m (UVvisible) for the first-generation instrument (with plans for future extensions to 1.5 m [micrometres] in the near-infrared). ■ Telescope rotates in azimuth on 8 air bearings to acquire targets, with a precision of 3m. A tracker with 10 degrees of freedom, with a positioning accuracy of 5 m in space, then follows the target, as the Earth rotates, for up to about 3 hours. It can be moved from one target to another in under 5 minutes. ■ Optical fibres will relay light from objects in the field of view to instruments in the basement room beneath the telescope. ■ The tracker has an effective diameter of about 4.5 m and, combined with the obscuration by the bridge on which it rides, reduces the light
collecting area to 57.3 m2. It supports a prime focus payload, consisting of instrumentation that includes an efficient camera and imaging spectrograph capable of observing many objects at once. ■ The concrete ring forming the base of the telescope pier is the smoothest, flattest piece of concrete ever cast in South Africa, deviating by no more than 1 mm from a flat plane over its ~50-m circumference. ■ SALT’s novel design as a fixed-elevation (53 degrees above horizon) telescope constrains the field of view to an annulus covering 12.5% of the sky at any one time, or 70% of the observable sky, and greatly reduces engineering costs. ■ All observation time on SALT and HET is ‘queue-scheduled’, a unique feature among ground-based telescopes that is more akin to satellite operations. Astronomers tell SALT what they want observed and for how long; then SALT generates a queue of observations for when the desired object is most efficiently accessible to the telescope; finally, the data
are recorded and sent electronically via the Internet to the proposers (who don’t need to be physically present). The complex scheduling takes into account factors including weather conditions and cloud cover, and the number of observations and time intervals requested. The SALT partner institutions each receive a fixed percentage of the total viewing time. ■ Many different observational programmes can be carried out efficiently in one night. ■ SALT is able to undertake a wide variety of scientific studies. It can • detect rapid variations in brightness and motion of many different types of object, allowing the study of the most extreme physical processes • take images through narrow-band colour filters, building up virtual 3D images of objects • look for polarized light from highly magnetized regions or where scattering is taking place • observe very faint, distant galaxies.
A day in the life of SALT attached to the SALT building) is opened to prepare for mirror alignment. Once the dome is opened, the mirrors are aligned using the equipment in the CCAS tower. The SA on duty in Sutherland arrives. Nightfall After the mirrors have been aligned and darkness has fallen, the observational work of the telescope begins. Details of the first astronomical target are transferred from the SALT database to the SO’s computer. The SA does this manually or uses the automated computer-controlled queuescheduling system. The SO initiates the pointing of the telescope at the target: ■ the dome rotates ■ the telescope structure rotates on air pads and is then ‘set down’ into position ■ the tracker is positioned at the start of its ‘track’ for receiving light from the target and begins to move ■ the instrument on the tracker starts observing the target ■ the SA’s computer receives an image (or spectrum, depending on the instrument that is being used) ■ the SA is able to change the exposure time, set the instrument mode (for example, filtering different colours or wavelengths), and change the configuration of the charge-coupled device (CCD) – the detector used on all SALT instruments ■ the data are immediately copied to a separate computer for ‘quick-look’ reduction and analysis so that the SA can verify that everything is working as expected (this is because the astronomer whose requested observations are being performed is probably not present at the
time). Meanwhile, the SO monitors the functioning of the telescope, its subsystems, and, of course, the changing weather. During the night, the SA instructs the SO to point to different target fields, typically from half a dozen to 15 times. They may observe hundreds, or even thousands, of astronomical objects during one night, such as asteroids in our Solar System, eclipses of wildly varying binary stars, signals from effects around black holes in our Galaxy or supermassive ones in distant active galactic nuclei, nearby spiral galaxies, and extremely faint galaxies at the edge of the visible Universe. Midnight SO change of shifts, with a half-hour handover period. Sunrise With the night’s observing completed, the SO ■ parks the telescope and tracker in a position giving easy access to the day staff for maintenance work ■ closes the dome ■ closes the louvres ■ switches off the false-floor fan ■ switches the power to standby mode. Before the SO initiates instrument calibrations, the SA prepares a detailed calibration sequence on the instrumentation that was actually used during the night (most of the scientific data taken would be useless without accurate information about the configuration and performance of the instrumentation). Now the SA and SO can get some sleep!
– Petri Vaisanen, SALT Astronomer (assisted by Lisl Robertson and Phil Charles) For more, visit www.salt.ac.za/content/observing/ pop3.htm; view the Sutherland night sky in real time with our webcam at http://nightskylive.net/sa/. ▲ ▲
Daytime Daylight hours at SALT are used for instrument adjustments, engineering duties, mirror cleaning and re-aluminizing (performed annually, at a rate of two segments per week), and other tasks to keep the telescope in good working order. The daytime SALT Astronomer (SA) on duty in Cape Town deals with the new scientific information collected during the previous night, checks and processes the scientific data, and sends them to Africa, Europe, North America, and New Zealand to the astronomers who have requested them. Early afternoon The air conditioning turns on automatically, to have the telescope at the same temperature as the outside air at dome opening time that evening. The telescope electronics and other electrical equipment are a significant source of heat, so they are housed in large, cooled cabinets (locally called ‘igloos’) whose doors must be kept tightly shut. 4 p.m. The SALT Operator (SO) starts the evening shift, and ■ checks the temperature control ■ (once the engineers and technicians have left the telescope) checks the dome, louvres, and fans, and makes sure that the telescope structure can move freely ■ makes sure that the lights are switched off and that the blinds in the building are closed (light leakages can contaminate the observations of SALT and the other telescopes on the plateau). Sunset The SO opens the dome and turns on the fans, which ensure a good flow of air from inside to outside, to minimize temperature gradients. The shutter of the centre of curvature alignment system (CCAS) (that is, the tall ‘chimney’
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Fact file Q Astronomy to empower the country ▲
As democratic South Africa’s pre-eminent ‘big science’ project, SALT has played a flagship role in promoting local industry during its five-year construction and in developing science competency, training, education, and research for its estimated 25-year lifespan.
Benefits to industry South African industry benefited directly from the construction of SALT and from the mix of local and international involvement. ■ As much as 60% of SALT’s construction budget was spent locally (only about 34% of its cost was paid for by South Africa). ■ The telescope was built by South African industry and involved civil, structural, mechanical, electrical, electronic, optical, software, and consulting engineers. Most of its major subsystems (such as the telescope structure, tracker, and dome) were designed and built by South African companies. SALT’s employment policy specifically supported black economic and technical empowerment. ■ Local industry gained experience in developing sophisticated components and subsystems, either by manufacturing them locally or by collaborating with companies abroad in building the specialized components. Science and engineering students were involved during SALT’s construction to gain work experience in this large, complex, high-tech project.
South African by design ■ 60% of SALT’s components were made in South Africa. ■ SALT’s aluminium dome and the mounts for the mirror segments were built in South Africa, and the aluminium coating plant for the mirror segments was installed by a South African company. ■ All the software that controls the mirror alignment was written by a South African company. ■ The drives, controls, and software for the dome, structure, and tracker, and all the fibre optics, air ducts, fans and valves were sourced from local companies.
Above: Primary mirror segments installed. Local industry was involved in all aspects of the construction of the SALT telescope.
Overcoming apartheid’s legacy South Africa’s past educational inequalities marginalized great numbers of students, especially in the sciences and mathematics. SALT has provided an opportunity to address these imbalances and to inspire future scientists and engineers of all races. SALT facilitates South Africa’s collaboration with other African countries’ space science and astronomy programmes after years of isolation. Much work will be done through the Working Group on Space Sciences in Africa (WGSSA),
SALT has been a catalyst for education projects around Sutherland to benefit formerly marginalized communities and institutions. These include: ■ The subsidized appointment of a mathematics and science teacher at the Sutherland High School. ■ For high schools in the Karoo Hoogland: tours of the observatory; science clubs; donations for laboratory materials and basic equipment; bursaries for studying mathematics and science at matric level and a bursary for study at tertiary level. ■ Sponsorship for school trips to attend the annual SALT Science, Engineering and Technology Careers exhibition in Cape Town (August) and the National Science Festival in Grahamstown (March). ■ For teachers: assistance with subject content, practical science and mathematics, and computer literacy; sponsorship to attend educational seminars and workshops; selection of teachers to participate in the Wisconsin Teacher Enhancement Programme at the University of Wisconsin, USA. ■ Joint SAAO and Northern Cape Education Department initiative to establish a mathematics and science academy in Sutherland, drawing young people from surrounding areas and upgrading Sutherland’s existing schools to accommodate it. ■ Establishment of visitor centres in Sutherland and Cape Town and collaboration with science centres around South Africa. currently coordinated at the SAAO. Astronomers, other scientists and engineers visit from African countries including Ethiopia, Uganda, Mauritius, Kenya, Nigeria, Zambia, and Egypt. SALT’s name (emphasizing ‘Southern’) reflects South Africa’s commitment to extend the project’s benefits to countries in our region through the Southern African Development Community (SADC). ■
Careers in S&T Q In astronomy, the sky’s the limit! South Africa’s astronomical vision is to remain world-class, and the country’s observatories have joined forces to promote astronomy and related disciplines. Whatever your background, you can benefit from outreach programmes at high school and specialization later, with top jobs in astronomy and many other fields.
African astronomers for the future The SALT and Karoo Array Telescope (KAT) projects will help to make the country a southern
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hemisphere astronomical hub. But South Africa has not been producing enough home-grown astronomers. Accelerated programmes to develop our own researchers to staff such facilities are crucial. A collaborative postgraduate National Astrophysics and Space Sciences Programme (NASSP) has been set up by South African universities offering astronomy, astrophysics, and space science (that is, Rhodes University and the universities of Cape Town, KwaZulu-Natal, Free
State, North-West, South Africa, Witwatersrand, and Zululand). Theory is supplemented with practical work at the Sutherland Observatory, the Hartebeesthoek Radio Astronomy Observatory, and the Hermanus Magnetic Observatory. First implemented in 2003, the programme takes candidates from South Africa and other African states and aims to benefit the continent as a whole. In addition, the SALT partners have established the Stobie-SALT Ph.D. Scholarship for the completion of doctorates in the USA or the UK.
Skills and qualifications Academic and practical skills: You need to be good at physics and maths, and have computer and programming skills for analysing astronomical data. Some astronomers build their own instruments, which means learning about electronics, materials fabrication, and other aspects of engineering. Good observation skills are essential – astronomers have to see clearly and make sense of what they see. They’re typically analytical, logical, and capable of sound reasoning. They need teaching skills if they’re academics, and writing skills for preparing proposals to get money and telescope time and for publishing in scientific journals. Communication skills are increasingly important, with so many professional collaborations conducted over the Internet, and with the need to engage the public’s interest. People skills: Astronomers work in groups, so teamwork is important, and effective public speaking at professional meetings is a must! Personal characteristics: Most valuable are patience, attention to detail, persistence, and the determination to see a difficult problem or theory through. High school preparation: Mathematics and science courses after grade 10 give the best chance of success in science or engineering. Involvement in high school science groups and amateur astronomy clubs is a great start! Further education: To study astronomy, you can begin with an undergraduate degree in the physical sciences or engineering, for good basic training in physics and mathematics and to acquire good computer skills. After that, you could proceed to a master’s, then a doctorate in astronomy. Through NASSP, students can get experiential training and project opportunities in different parts of South Africa at honours and master’s levels, and research assistantships during their doctoral work.
What astronomers do At universities and colleges, or observatories and laboratories, astronomers teach and conduct research. Observational astronomers spend 10–30 nights a year working at an observatory or getting observations from spacecraft, and the rest of their time analysing their data. Others, such as theoretical astrophysicists, may conduct
Busy in the electronics workshop at the SAAO.
Dealing with disaster
Student training session in the mechanical workshop. Photographs courtesy of the SAAO
their research using supercomputers. Astronomers are often classified by subject speciality: planetary scientists study planets and moons; stellar astronomers study stars; solar astronomers study the Sun; extragalactic astronomers study the many different galaxies and the structure of the Universe; cosmologists study the origin and evolution of the Universe. They could also specialize in telescope types – radio astronomers study different objects with radio telescopes – and instrumentation specialists build new equipment. Astronomers often combine specialities.
Other career opportunities? Astronomy is helpful for learning basic concepts of physics and for training in problem-solving. Since physics underlies all modern technology, graduates in astronomy and astrophysics are in demand in a wide range of careers. In planetariums, science museums, libraries, and other public service positions, they bridge the gap between professional astronomy and the general public, as do science journalists. Some teach physics or earth sciences in secondary schools. For these careers you don’t need an advanced degree. An undergraduate major in astronomy or physics can get you a support job at a national observatory, national laboratory, or university. Astronomical facilities need technical support staff such as telescope operators, observing assistants, and optical engineers. They also need administrative assistants, electronic technicians, and accountants, so there are many ways to work in this environment. Studying astronomy can prepare people for careers as laboratory technicians and computer programmers, and for work with instrumentation, remote sensing, spectral observations, computing, and image processing. Salaries can be good, especially at middle management levels and above. ■ For more, visit www.star.ac.za; www.saao.ac.za; and www.hartrao.ac.za. There’s useful and wide-ranging careers information in the Department of Science and Technology’s Careers in Science, Engineering and Technology (Pretoria: Beyond 2000 Publishers in association with the DST, 2005).
A South African first for TB research A milestone was reached in September 2005 in the history of South African molecular biology with the sequencing of the first strain of Mycobacterium tuberculosis to be sequenced from our continent – the first drug-resistant strain and only the third M. tuberculosis genome (the second clinical isolate) to be fully sequenced worldwide. This work is part of ongoing investigations into the spread of M. tuberculosis, explains Paul van Helden (see QUEST, vol. 1, no. 4, “Genomics fights TB”). Not until the 1990s was a reliable method devised for classifying different strains of the bacterium that cause disease, thus permitting the development of the new science of molecular epidemiology. Now, a sequencing consortium of US researchers (at the Harvard School of Public Health and the Microbial Sequencing Centre of the Broad Institute) and researchers based at the University of Stellenbosch (DST/NRF Centre of Excellence in Biomedical Tuberculosis Research/MRC Centre for Molecular and Cellular Biology) have joined to sequence the genomes of eight common strains of M. tuberculosis. The drug-resistant F11 isolate, selected from the University of Stellenbosch M. tuberculosis clinical strain bank, is the first of the eight to have been fully sequenced. Bacteria from this strain family account for more than 20% of all cases in the epidemiological field site near Cape Town. They are also significant in the global TB epidemic. Insight into the biology of these strains will help scientists to discover what makes F11 so efficient a pathogen and to understand better the genetic mechanisms leading to drug resistance. For more visit www.broad.mit.edu/annotation /microbes/mycobacterium_tuberculosis_f11/. Lessons from cyclones Devastations caused by natural disasters such as the tsunami of 26 December 2004 and more recent hurricanes along the US Gulf coast have put the spotlight on the relationship between science, government, and disaster management worldwide. Hurricane Katrina provides sober lessons. ■ In 2004, a New Orleans simulation exercise, with a fictitious category 3 hurricane named Pam, accurately predicted the Katrina scenario, but funds to prevent the devastation were not allocated. ■ The US government in January 2005 issued a National Response Plan to provide “the means to swiftly deliver federal support in response to catastrophic incidents”. Katrina put the Plan to the test: it failed. How in practice should taxpayer-funded scientific research be turned into implementable policy – in the USA and elsewhere? What collaborations are needed for science and government to work together successfully? We stay tuned.
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Many discoveries have come from the Sutherland station of the South African Astronomical Observatory (SAAO). Astronomers from the SAAO and the University of Cape Town describe a few of the more interesting and recent results. Above: Infrared image of the central one square-degree of the Milky Way, formed from about 36 individual images taken by the Japanese 1.4-m telescope at Sutherland. The Galactic Centre cannot be seen in ordinary light because it is hidden by the dust between the stars. This is a falsecolour image, formed from individual exposures through three infrared filters. About one photon (light particle) in ten can reach us in the infrared, compared to only one in a million million in the visible spectrum. The observations were part of the IRSF/SIRIUS project by Nagoya University and the National Astronomical Observatory of Japan in collaboration with the SAAO. Picture courtesy of SAAO.
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The distance scale of the Universe Michael Feast, SAAO and the University of Cape Town The picture of this spiral galaxy, NGC6744, taken by SALT as one of its ‘first light’ images (next page) is very spectacular. But how big is the galaxy and what is it made of? To answer these questions we need to know its distance. The relative distances of galaxies are measured by the relative brightness of objects that they contain. To put these distances on an absolute scale (that is, in kilometres or light years) we need the true distance of at least one galaxy. The first galaxies for which true distances could be estimated were the Magellanic Clouds
– two nearby, small galaxies that are in the southern sky and just visible as fuzzy patches to the naked eye (at a dark site, like Sutherland). South African astronomers have become experts in the study of these galaxies and have obtained the first accurate estimate of their distances. Some of the stars in the picture of NGC 6744 pulsate, getting regularly brighter and then fading as the star expands and contracts. This allows astronomers to recognize them. Comparing their average brightness to that of similar pulsating stars near the Sun, whose distances we know, gives us the distances of the Magellanic Clouds. These distances can then be used to place all the relative distances on an absolute scale. In this way, we find that the NGC6744 galaxy is about 30 million light years
Immediately above: NGC 6744, a large spiral galaxy about 150 000 light years across, has more than a hundred thousand million stars. Like other spiral galaxies, its bright nucleus is dominated by older, reddish and yellowish stars, while the widely and thinly spreading spiral arms are home to bluer, younger ones. In this ‘first light’ image from SALT, the fuzzy blue spots along the spiral arms are hot, star-forming regions, and dark lanes and patches show dust, which obscures the light of the stars.
away (or, in kilometres, 3 with 20 noughts after it). We can estimate, too, that it is 150 000 light years in diameter and contains about 100 billion stars, some of them very much brighter than our own Sun. From work of this kind we know that we live in a Universe that is many millions of light years in size. For more, visit these three web sites: http://antwrp.gsfc.nasa.gov/apod/ap980203.html; http://antwrp.gsfc.nasa.gov/apod/ap980124.html; and http://heasarc.gsfc.nasa.gov/docs/cosmic/cosmic.html.
Light echoes reveal the structure of interstellar space Lisa Crause, University of Cape Town
Top panel: The ‘first light’ images from SALT reveal the telescope’s great light gathering power. When the active optics control is fully implemented, images will be even sharper. ‘First light’ images courtesy of the SAAO/SALT Foundation
specific samples of stars to build up an understanding of how their lives progress. The process is something like trying to decipher the course of human development and to investigate human behaviour on the sole basis of photographs of crowds of people. The chance of catching someone blinking in a photograph is quite good, as everyone blinks, and often. But short-duration events that happen less frequently, like a sneeze, are less likely to be captured in such a snapshot. Occasionally though, we get the chance to study stars going through brief, quite dramatic, evolutionary phases. Such events test and help to constrain theoretical models for various types of stars and their physical processes – often raising new questions and sometimes ▲ ▲
Astronomers rarely witness stellar evolution on human timescales – we normally have to study
Immediately above: NGC 346 in the Small Magellanic Cloud. This is a young cluster of hot, massive stars embedded in clouds of gas from which they recently formed. Picture from the Hubble Space Telescope courtesy of NASA, ESA, and A.Nota
Top left: This ancient, globular star cluster, 47 Tucanae, is about 10–12 million years old (more than twice as old as our Sun), 120 light years across, and 15 000 light years distant from Earth. Top middle: NGC 6530: a cluster of 50–100 stars, which formed some 2 million years ago. The hottest and most massive cluster member is about 40–50 times the mass of our Sun and hundreds of thousands of times brighter. Top right: A small part of the Small Magellanic Cloud, one of two nearby small galaxies that are fuzzy patches visible only in the southern skies and just visible to the naked eye, but beautifully resolved here by SALT into a vast number of stars.
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Picture courtesy of NASA/HST
Right: The key features of an interacting X-ray binary system (visualized here by former Southampton astronomer, Rob Hynes). The companion star is transferring gas through an ‘accretion stream’ as it orbits (every few hours or days) around a neutron star or black hole (which resides in the centre of the ‘accretion disc’). Angular momentum (that is, the momentum that a body has by virtue of its rotation) means the gas cannot fall directly onto the compact object but must form the disc. Eventually, matter from the disc does accrete in the centre onto the (unseen) compact object, releasing vast amounts of gravitational potential energy, heating the gas, and emitting X-rays. The luminosity can be so great that it drives some of the accreting gas out of the disc, which we see as a ‘jet’ or ‘disc wind’. Only about 200 of these exotic objects are currently active in our Galaxy. Lower right: Motion of the companion star as it moves in its 10-day orbit around the unseen compact object. The amplitude of this motion tells us the mass of the compact object.
completely overturning existing theories. V838 Mon offers the best recent example of such an event. This instance of a bizarre newlydiscovered type of variable star1 suffered three major eruptions in 2002, then expanded to supergiant proportions and cooled several thousand degrees in just a few months. At its brightest, in February 2002, V838 Mon was the most luminous star in the Milky Way, and a light pulse from that outburst, which is scattered by dust near the star, produced the light echo (shown in the panel above). The nature of a light echo is such that each image captures specific information about the three-dimensional structure of the dust, producing a kind of ‘astronomical CT scan’ of the scattering material. This offers a unique opportunity to study interstellar dust2 that would otherwise have remained invisible to us. Furthermore, measuring the expansion of the echo allows us to estimate the distance to the star, which will help to discriminate among the various models proposed to explain the star’s unprecedented behaviour.
is the value that decides the borderline between the two? That is, how heavy can a neutron star be before the force of gravity collapses it into a black hole? This astonishingly important number has implications for our understanding of the nature of matter itself, yet it has proved extremely difficult to identify objects close to this border. The problem is that whereas neutron stars are relatively easy to identify – they pulse regularly (as radio pulsars do) – black holes have fewer clear-cut features (by definition their surface cannot be seen!). Consequently the hunt has been on for a binary system (or, a double star) where one member is a compact object accreting material from its companion star (see diagram below) and where the characteristic pulsation signature of a pulsar is absent. Such a double star (called V395 Car5) was observed with the 1.9-m telescope at Sutherland in 2004, and the motion of the red giant companion
For more information, consult two online articles at: skyandtelescope.com/news/current/article_840_1.asp and www.aavso.org/vstar/vsots/1202.pdf
Borderline between neutron stars and black holes Phil Charles, SAAO It is almost 40 years since the discovery of extremely small, superdense objects called neutron stars3, and, shortly afterwards, the term ‘black hole’ was coined to describe the most exotic compact object of all, whose density is so high that its escape velocity (that is, the minimum velocity required to escape from a gravitational field) exceeds that of light itself. Both neutron stars and black holes are created when massive stars come to the end of their lives and collapse as ‘supernova’ explosions4. Much material is ejected, but the core of the star is compressed into either a neutron star, of mass close to 1.5 times that of the Sun yet only about 20 km across, or a black hole, whose masses have been measured in the last decade to be in the range of 5–15 times that of the Sun. But what
200 Heliocentric Radial Velocity (km/s)
Above far right: A higher resolution image taken from the Hubble Space Telescope, showing the structure of interstellar space near V838 Mon.
Above (three-part panel): V838 Mon is the red star near the centre of this expanding light echo, images of which have been obtained regularly with the SAAO 1-m telescope. The panel shows the evolution of the echo between May 2002 and March 2004.
150 100 50 0 –50 –100 –150 0.0
0.6 0.8 1.0 Orbital Phase
1. Variable star: any star whose appearance varies in brightness. This can be for mechanical reasons (for example, rotation) or because they undergo real change in luminosity, either as an individual star or because of some element in a binary system. Some stars combine both types of variation. V838 Mon is a variable star (indicated by the “V” in the name) in Monoceros (“Mon”), a constellation on the celestial equator (see panel above). 2. Interstellar dust (or, interstellar matter): the material between the stars, which, in our Galaxy, comprises 99% gas and 1% fine dust particles by mass. It is the reservoir of material from which new stars form. 3. Neutron star and black hole: A neutron star is formed when a massive star undergoes a Type II supernova explosion, during which the core of the massive star collapses under its own gravity until electrons and protons are so closely packed that they combine to form neutrons. It is supported against further gravitational collapse if its mass is no greater than about 2 solar masses. (The greater the mass of a neutron star, the smaller its diameter.) If the object is more massive than this limit, it collapses further into a black hole. 4. Supernovae: violent explosions in which certain stars end their lives. In such an explosion, the star may become over a billion times brighter than the Sun, and for weeks may outshine the entire galaxy in which it lies. The last supernova visible to the naked eye was Supernova 1987A in the Large Magellanic Cloud. 5. V395 Car is a variable star in the southern constellation Carina.
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was detected in its 10-day orbit. The scale of this motion tells us how heavy must be the (unseen) compact object around which the companion is moving, as the heavier the compact object, the faster the companion has to move. Remarkably, V395 Car is a binary system with a compact object mass of around 2–3 times that of the Sun yet it does not appear to be a neutron star. If it is a neutron star, then it is the most massive yet found, but it may turn out to be one of the elusive low-mass black holes, which theory has predicted but which have not yet been discovered. For more, read P.A. Charles and R.M. Wagner, “Black Holes in Binary Stars: Weighing the Evidence”, Sky & Telescope (May 1996); M. Begelman and M. Rees, Gravity’s Fatal Attraction: Black Holes in the Universe (Scientific American Library, 1996). For a huge resource list, visit imagine.gsfc.nasa.gov/docs/resources/ resources_a.html
Eta Carinae: the next Galactic supernova? Patricia Whitelock, SAAO Above and right: Two views of the hypergiant variable, Eta Carinae – optical Hubble Space Telescope picture (above) and X-ray Chandra satellite picture (right). The optical picture shows the central star surrounded by the bipolar Homunculus (‘little man’) Nebula (ejected in Eta’s great eruption 160 years ago). The X-ray picture shows the same star at the centre, surrounded by a blue region whose temperature is over 40 million degrees K. Picture courtesy of NASA/Chandra project, 1999
may well end spectacularly as one of the Universe’s most energetic events, a supernova gamma-ray burster. If so, it will make the brightness of the night sky approach that of day, and probably leave behind a different enigma – a black hole. For more, read Neil Gehrels, Luigi Piro, and Peter Leonard, “The Brightest Explosions in the Universe”, Scientific American (December 2002) and visit http://en.wikipedia.org/wiki/Gamma_ray_burst and http://heasarc.gsfc.nasa.gov/docs/xmm_lc/edu/lessons/ background-lifecycles.html
Clusters and superclusters of galaxies Patrick Woudt, University of Cape Town On a clear night in Sutherland, the furthest object that can be seen with the naked eye is the Andromeda galaxy, a big, nearby, spiral galaxy not unlike our own Milky Way, containing hundreds of billions of stars. The light we can see from this galaxy, travelling at the speed of light (300 000 km per second), has taken 2 million years to reach the Earth. Astronomers express such distances in ‘light years’, with the Andromeda galaxy 2 million light years away. Galaxies tend to cluster in space. The Milky Way (home to our Solar System) and Andromeda are the largest members of the Local Group of galaxies, which also includes the two Magellanic Cloud satellite galaxies. The Local Group itself is on the fringe of the Virgo Cluster (some 50 million light years away) and the Virgo ▲ ▲
In the 1840s, Eta (or, ) Carinae was the second brightest star in the night skies, rivalled only by Sirius. It was of great interest to astronomers, particularly those in the southern hemisphere where it was visible. Today it is 250 times fainter and, while we understand what happened in 1843 – Eta Carinae ejected its outer layers – we still don’t know why. At over 100 times the mass of our Sun, Eta Carinae is possibly the stellar heavyweight champion of our Galaxy. It is also the archetypal astronomical object in the sense that it can be fully understood only through observations across the entire electromagnetic spectrum. Although most of its energy is emitted at infrared (IR) wavelengths (where it is the brightest object in the sky outside the Solar System), it provides an interesting source of study at all wavelengths from radio to X-rays, and has been mentioned in the abstracts of over 1 000 published papers to date, 400 of them since the year 2000. A totally unexpected discovery confirmed only very recently that Eta Carinae is, in fact, a binary system comprising two stars in highly eccentric orbits that take just over 5.5 years to complete. The most convincing evidence for this periodicity comes from IR observations made from SAAO over the past 34 years. The more we learn about this enigmatic object the more we want to know. We now understand that stars similar to Eta Carinae (that is, of comparable mass) and even more massive ones must have been common among the very first generation of stars formed in the early Universe, around 13 billion years ago. We know very little about these hypergiants, whose influence we are just starting to probe with the world’s very biggest telescopes, but Eta Carinae offers the opportunity to study one such object relatively close up. It will have a very short lifetime (barely a million years, which is 10 000 times shorter than that of our own Sun!) and
Above: A near-infrared image of galaxies in the rich Norma cluster at the heart of the Great Attractor. The great number of stars in the foreground (all part of our Galaxy, the Milky Way) made it difficult in the past to map the Great Attractor fully. This image was taken with the SAAO’s 1.4-m near-infrared telescope at Sutherland.
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Cluster, in turn, is part of a network of galaxies forming a ‘great wall’ of galaxies over a distance of 200 million light years. Astronomers at the University of Cape Town (UCT) have used the SAAO’s 1.9-m telescope at Sutherland in the last decade to study the clumpy and clustered distribution of galaxies in the Local Universe. In particular, they have identified the centre of the concentration of galaxies called the Great Attractor. This is so massive (models predict a mass of 50 000 000 000 000 000 – 50 million billion – times the mass of our Sun!) that our entire Milky Way is being gravitationally drawn towards it at a speed of 500 km per second. SALT is opening up outstanding new possibilities for the study of the distribution of galaxies on the largest scales. UCT plans to use SALT to study superclusters similar to the Great Attractor but now at incredibly large (cosmological) distances. The light coming from some of these far-off superclusters has taken 6–7 billion years to reach the telescope. When the light left them, the Universe was only half its current age (the estimated age of the Universe is around 13.5 billion years). With SALT, therefore, we will see the ‘young’ Universe and gain the possibility to probe the evolution of its contents – galaxies, clusters, and superclusters. SALT is not only Africa’s giant eye on the Universe but also a time-machine that allows us to see the Universe as it once was. For more information, visit these three web sites: http://map.gsfc.nasa.gov/m_uni/uni_101structures.html; http://imagine.gsfc.nasa.gov/docs/features/topics/clust ers_group/clusters_intro.html, and http://chandra. harvard.edu/xray_sources/galaxy_clusters.html
First science with SALT: viewing structure on a supermagnetic white dwarf Darragh O’Donoghue, SAAO Some features of SALT and its instruments were specifically designed to investigate some of the closest binaries we know (called ‘polars’). The orbit of the two stars would actually fit inside the Sun (!) and they orbit each other in only 2 hours or so (compared with a month for the Earth and Moon, and a year for the Earth and Sun). Although a double star system, these stars are so close to each other that they appear as only one star in a telescope. One of the pair is similar to the Sun (in that it is also a cool, low-mass star), only cooler, redder, and about 30% of the mass and radius of the Sun. The other star is a very dense white dwarf6: its mass is similar to the Sun’s, but squeezed into the size of the Earth (whose diameter is about 1% of that of the Sun). The amazing thing about these binaries is that the white dwarf is gravitationally sucking the outer layers off the cool, red star. In addition, the white dwarf has a huge magnetic field
6 August 2005 Eclipse 1 (Sec)
Top: Imagine a binary system in which a white dwarf is sucking the outer layers off a cool, red star. If you look at this event from ‘behind’ the cool, red star, with the viewing angle shown, then the red star, once per orbit, eclipses (blots out) light from the white dwarf. This schematic shows your view of the system at the start of the eclipse (left) when the red star is just about to eclipse Spot 2 (on the white dwarf), and at the end of the eclipse (right) when the red star has passed by to uncover Spot 2 and make it visible once more. Above right: This painting shows a typical magnetic ‘polar’ binary system: the cool, red star is in the background with the stream of gas shown in white, threading its way along the powerful magnetic field onto the white dwarf’s two polar caps (lower right). Artist: Bob Watson Above left: With the SALT telescope, and its SALTICAM camera, which can make brightness measurements every 200 milliseconds, you can see the brightness of the system dim as the cool, red star eclipses the bright spots on the white dwarf (shown on the right of the schematic, [top]).
(30 million times the Earth’s magnetic field), channelling onto its own magnetic poles the gas coming off the cool star. The light from the gas crashing onto the magnetic poles of the white dwarf totally outshines the light from everything else. The above graph shows a sequence of brightness measurements from SALT showing exactly what is described in the schematic picture (top). If you look closely at the graph, you will see it has a first sudden brightness drop (Spot 2 disappearing), followed a few seconds later by a second sudden brightness drop (Spot 1 disappearing). Towards the end of the sequence, there are sudden rises in brightness corresponding to the earlier sudden drops as the spots are appear again. The gas stream between the stars also gives some light, which accounts for the rounded shape of the bottom of the eclipse. This sequence of measurements is better than anything obtained before, and will be included in the first paper (or report) on the science from SALT. ■ For more, visit http://imagine.gsfc.nasa.gov/docs/ science/know_l2/cataclysmic_variables.html
Look up details and explanations in Ian Ridpath (ed.), A Dictionary of Astronomy (Oxford University Press, revised edition, 2003), and consult Anthony Fairall, Starwatching – a southern hemisphere guide to the galaxy (Struik, 2002). For more on the SAAO and its discoveries, visit www.saao.ac.za
6. White dwarf: a small, dense star that forms at the end of the evolution of all except the most massive stars. They form from the gradual collapse of stellar cores after nuclear burning has ceased. The core contracts through its own gravity until it is as small as the Earth and so dense that it stops collapsing. When formed, white dwarfs have high surface temperatures, then they gradually cool, becoming redder and fainter. Their low luminosity makes them inconspicuous.
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Right: The Sun (left) emits charged particles towards the Earth (right), in a continuous stream (the solar wind). Unable to cross the Earth’s magnetic field, they’re channelled along the field lines onto the Earth’s magnetic poles, interacting there with the Earth’s upper atmosphere in the spectacular light shows visible from the ground as the aurora borealis (northern hemisphere) and, simultaneously in the southern hemisphere, the aurora australis. Image courtesy of NASA.
Peter Sutcliffe and Pieter Kotzé explain the workings of the Earth’s magnetic field and what makes our region unique.
Unique to southern Africa Unique to the region close to southern Africa is a feature called the South Atlantic Anomaly (SAA), where the geomagnetic field is weaker by about 40% relative to other places on the Earth at equivalent latitudes. This weaker field allows highenergy particles to penetrate deeper into the upper atmosphere here than anywhere else on Earth. The space science community knows the hazards of this region, as most spacecraft crossing it at altitudes below 1 000 km have experienced some kind of damage or degradation (solar panels, on which they depend for the generation of electricity, can get damaged here, for example, as can computer chips; and astronauts are vulnerable to radiation in this area). Outside the space community, however, few people recognize the implications. By the year 2100, the SAA will cover most of South America, the southern part of Africa, and the South Atlantic Ocean south of approximately 25° S to the Scotia Sea and Antarctica. The size of the SAA will have increased by a factor of 4, which suggests that the radiation hazard to humans in space may increase correspondingly. This change will affect the geomagnetic equator, and possibly change long-range high-frequency radio transmissions.
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f you suspend a bar magnet at any point on the Earth’s surface and allow it to move freely, the north-seeking end points in a northerly direction. This is because of the planet’s magnetic field, which – though it varies irregularly from decade to decade in intensity and direction – has given generations of navigators an idea of the direction in which they might be travelling. The ancient Chinese, for instance, formed a simple magnetic compass by suspending a piece of lodestone from a fibre. But it wasn’t till 1600 that William Gilbert laid the foundation of the science of geomagnetism in his book De Magnete, where he stated that “the Earth itself is a great magnet”. Early explorers made isolated observations of the geomagnetic field, but understanding its global nature required simultaneous observations at many places on the Earth’s surface so that measurements could be compared. In 1932, the International Commission for the Polar Year asked Alexander Ogg, professor of physics at the University of Cape Town, to establish a magnetic observatory. Housed on the university campus, it received its funding and instruments from institutions abroad. By 1940, the developing suburban electric railway system in Cape Town was interfering with the geomagnetic field observations: it was time to relocate. A ‘magnetically clean’ site was found in Hermanus and the new Hermanus Magnetic Observatory (HMO) officially started operations on 1 January 1941. Since then, it has produced globally interesting – and disturbing – results. Earth’s shield At distances closer than about 25 000 km to the Earth’s surface, the geomagnetic field is a bit like a gigantic bar magnet. People can’t detect it
through any of their natural senses, but, without it, billions of years of solar wind would erode Earth’s atmosphere, and life on Earth as we know it would be unable to exist. (This, for instance, is what we believe happened on Mars – its magnetic field progressively weakened when the core of the planet solidified, so now it does not have a strong, global magnetic field, only localized areas that are weakly magnetized.) The geomagnetic field shields animals and humans against the damaging energetic particle radiation from the Sun and from other energy sources in space. Many animal species (from pigeons to whales) can use its orientation for navigating, and people also use it in all kinds of ways – to guide missiles, for instance. Even now, despite our sophisticated global positioning systems (GPS), every aeroplane is obliged to carry a magnetic compass for navigation in case lightning, for instance, damages its electronics. Is another field reversal due? The study of palaeomagnetism (that is, magnetism in rocks in the geological past) indicates that our geomagnetic field periodically undergoes reversals, when the geomagnetic north pole becomes the south pole, and vice versa. During the Earth’s history, these poles have reversed many times at intervals ranging from about 120 000 years to 660 000 years. South Africa is uniquely positioned for studying such geomagnetic field changes. According to a 2002 research report based on satellite data, a reverse dynamo may be developing in the molten layer some 3 000 km underneath the surface of the Earth below the southern tip of Africa. This could be leading to another geomagnetic field reversal (similar to the last known reversal 780 000 years ago, and
Solar Flare Protons
Energetic Electrons Damage to spacecraft electronics
GPS Signal scintillation
HF Radio wave disturbance
Radiator effects on crew, passengers and avionics
Geomagnetically induced currents in power systems
Induced effects in submarine cables Telluric currents in pipelines
Magnetic interference in exploration surveys
Above: Ways in which space weather storms can affect technology. The hazards have become more significant with developments in human technology. This is why space physics research tries to improve our ability to predict space weather correctly. Image courtesy of Natural Resources Canada.
already overdue by about 250 000 years). During such a reversal, the geomagnetic field decreases to about 10–20% of its current maximum strength1, with implications for animals as well as people. It reduces the shielding effect, for example, exposing them to greater radiation from space. At present, the Earth’s magnetic field is decreasing relatively rapidly (it has decreased by as much as 20% at Hermanus since 1940) and some scientists believe that this marks the start of the next, inevitable reversal. A reversal takes a long time (from some two thousand to five thousand years), and similar reversals have not in the past been associated with massive extinctions of species. Some scientists expect that wild animals and birds, for instance, would have time to adapt to the changes. For humans, a weakening geomagnetic shield could increase the incidence of cancer and other radiationrelated illnesses. But high-tech human societies are probably the most vulnerable, given modern civilization’s need for power grids and satellites, which even now are affected by variations in the magnetic field during geomagnetic storms. We have no complete record of the history of any reversal, so whatever claims we make are based mainly on supercomputer-based mathematical models of the field’s behaviour and partly on limited evidence from rocks that still bear an imprint of the ancient magnetic
field present when they were formed. We might expect, however, during a reversal, to see a very complicated field pattern at the Earth’s surface, with perhaps more than one north and south pole at any given time. The poles might ‘wander’ from their current positions towards and across the equator, and there might even be daily auroral activities at the equator. Nevertheless, at the Earth’s surface, the atmosphere acts as an extra blanket to stop all but the most energetic of the solar and galactic radiation. (Indeed, it shields us from high-energy radiation as effectively as a concrete layer some 4 m thick!). In the case of a weak magnetic field, therefore, our atmosphere would still stop most of the radiation. ■ Dr Sutcliffe is manager of the HMO, and his main research interest is in ultra-low-frequency oscillations of the magnetic field. Dr Kotzé heads the Geomagnetic Group and specializes in the long-term variations of the magnetic field. For more visit www.geomag.bgs.uk/education and www.spaceweather.gc.ca.
Above: Electric-blue aurora glowing on the giant planet Jupiter. The aurora’s main oval is centred on the magnetic north pole, with auroral ‘footprints’ from three of Jupiter’s largest moons – Io (along the lefthand limb), Ganymede (near the centre), and Europa (below and to the right of Ganymede’s auroral footprint). Image from the Hubble Space Telescope, courtesy of NASA.
HMO activities The Hermanus Magnetic Observatory (HMO) forms part of the worldwide network of magnetic observatories that monitor and model variations of the Earth’s magnetic field. It has four operational groups. The Geomagnetism Group studies and monitors variations of the Earth’s magnetic field, the derivation of geomagnetic field models and indices, and the distribution of geomagnetic field information. The Space Physics Group conducts research that helps us to understand plasma behaviour in the ionosphere and magnetosphere and its impact on Earth. The Science Outreach Group strives to create better understanding and appreciation of science and technology amongst school educators and learners and to promote public understanding of geomagnetism and space physics. The Technology Group provides quality-controlled magnetic field and sensor-related services to clients in the defence and aerospace industries on a commercial basis. For more details about the HMO visit www.hmo.ac.za
1. The local magnetic intensity of the field varies from about 20 000 nanotesla (nT) to 60 000 nT. It is higher near the poles than at the equator.
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The world’s most powerful very-high-energy gamma-ray telescope in Namibia has opened spectacular new views onto the Milky Way, reports Okkie de Jager – with some unexpected spin-offs for industry. Left: Two of the four fully steerable HESS telescopes. The shed in front of each is used to park its massive camera during daytime, when no observations are made. The camera has 960 ultra-sensitive light detectors, packed together like the composite eye of a bee. It is rigidly mounted in the focus of its telescope (15 m focal length), which has 380 mirror segments covering a total mirror area of 107 m2 per telescope. The total mirror surface of the HESS system is therefore 428 m2. Photograph: Courtesy of the HESS Collaboration
Great focus Born out of the most violent processes in the Universe, gamma-ray sources have been difficult to observe clearly till now because we have not
The launch of the Compton Gamma-Ray Observatory by the Space Shuttle Atlantis in 1991. Photograph: Courtesy of NASA Goddard Space Flight Center
had the instruments to explore their very high energies. NASA’s Compton Gamma-Ray Observatory (CGRO) spacecraft, launched some 15 years ago, has discovered more than a hundred gamma-ray sources in our Milky Way and other galaxies. But its space-based detection technique has a focus problem, and its images are too blurred to tell us if these gamma-ray sources are star-like (compact) or extended (nebulous)1. ▲ ▲
or thousands of years the Universe has intrigued astronomers – are we alone? how do we fit into the cosmos? First, astronomers looked at the visible sky. In 18thcentury Europe, they developed observation and the scientific method to expand their knowledge, and in the 19th century they began probing beyond what the human eye can see. Now, as the 21st century begins, SALT celebrates a highpoint of optical astronomy, while the High Energy Stereoscopic System (HESS) of telescopes in Namibia celebrates crucial steps in a very recently developed type of exploration – gamma-ray astronomy. As the world’s most powerful very-high-energy gamma-ray instrument, it has gone where none have gone before to open up new views of the energetic Universe and reveal more of its secrets.
Exploring gamma rays Gamma rays are produced in sites of the most violent processes in the Universe – regions of extremely high temperature, density, and magnetic fields. Whereas radio, infrared, visible, and X-rays hint indirectly at particle acceleration, gamma rays tell us directly the energies to which charged particles (such as electrons and protons) have been accelerated. Gamma-ray telescopes record gamma rays and use different methods to detect gamma rays at different energies. Highpoints of gamma-ray astronomy 1960s–1970s Balloons carried instruments to altitudes where the atmospheric absorption of gamma rays is low. 1960s Spacecraft (including Ranger and Apollo) made exploratory gamma-ray observations. 1970s Development of sky surveys and gamma-ray experiments. 1990s Launch of the Soviet Granat satellite (1989) and NASA’s Compton Gamma-Ray Observatory (1991). 1960s–1980s First Generation (non-imaging) ground-based Cerenkov telescopes could rarely see cosmic sources because of the lack of accurate Cerenkov shower reconstruction capability. 1990s Second Generation ground-based Cerenkov telescopes had imaging capabilities and could see a few sources in the sky. 2000+ Third Generation of Cerenkov telescopes. Also, the successful HESS era, where four telescopes, each with an 11-m mirror diameter, are placed on a square of 120 m sides to obtain ‘golden events’ (such as Cerenkov showers, which trigger more than one telescope to allow accurate ‘triangulation’ of the arrival direction and energy of the shower – which is what is meant by the ‘stereoscopic view’). So far, HESS has greater focus and sensitivity than other telescopes of its kind. August 2007 Planned launch of NASA’s GLAST, which is expected to have greater sensitivity and focus than the CGRO and the other previous spacecraft.
1. Compact or nebulous: A ‘compact’ source indicates that gamma-ray production is occurring in a small volume near a compact object like a neutron star or black hole. ‘Nebulous’ implies that high-energy particles have been ejected by a compact object into the interstellar medium into a large volume, producing gamma rays as they interact with matter or with relic cosmic microwave photons from the Big Bang.
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whether it is point-like or nebulous. In 2004, the telescope was able to produce the first ever spatially-resolved image of a gamma-ray source (see image, left). This newly-discovered distant star (at least 6 000 light years away from Earth) probably exploded about 1 700 years ago in a supernova (the violent explosion in which some massive stars end their lives). The shock wave of this kind of eruption expands faster than 1 000 km per second, trapping the nuclei of atomic particles. These particles (cosmic rays3) become more energetic till they’re able to escape from the fast expanding shock wave. Interacting with the gas in the shock, they generate very-high-energy gamma rays, giving a shell-like appearance (top left). Despite its enormous distance from Earth, the size of this newly-detected supernova shell is larger than the size of the full Moon in the sky (if we look from Earth). With the discovery of this exploding star, HESS took a great stride towards solving one of science’s greatest riddles: what is the origin of cosmic rays? According to our findings, they appear to originate in the shocks of supernova explosions, as was theorized in the late 1970s. Cosmic rays are important. Flight personnel spend time at high altitudes (about 10 km above the Earth’s surface) on many longdistance flights, and may suffer exposure to the radioactivity of cosmic rays. Furthermore, there is evidence to link global climate changes to variations in the intensity of the cosmic ray flux at the top of Earth’s atmosphere, so the more we know the better.
Above: HESS spatially-resolved image (that is, the image is sharp enough to reveal its structure) of the supernova remnant shell RX J1713.4-3946. The red parts indicate the brightest regions in gamma rays (forming a shell-type structure). The size of the full Moon in the sky is shown for comparison. Image courtesy of the HESS Collaboration. Published in Nature, vol. 432 (2004), p.75.
Diagram courtesy of the HESS Collaboration
Right: A very-high-energy gamma ray entering the Earth’s atmosphere at an altitude of 10 km produces a cascade of electrons and positrons (matter and antimatter) and, eventually, blue light (called ‘Cerenkov’ light) in the shape of a disc with a diameter of 240 m and 1 m thick. (In the process we use Einstein’s equation: E=mc2, where a gamma ray of energy E is converted into matter and antimatter of mass m.) An imaging camera with a shutter speed of about 500 million frames per second in the focus of a large optical telescope captures the image of this ‘shower’ of light.
The CGRO measures gamma-ray energies between 100 million and 10 billion times higher than those of visible light. The ground-based gamma-ray detection techniques of HESS and other similar telescopes, however, are more powerful: they probe gamma rays between 100 billion and 40 000 billion times higher in energy than those of visible light. At these incredibly high energies, a single ‘very high-energy’ gamma ray modifies our atmosphere at an altitude of about 10 km above sea level. It polarizes and ionizes molecules such as nitrogen and oxygen, converting the gamma ray into matter and antimatter – that is, electrons and positrons. These travel faster than the speed of light in air to create a light disk called Cerenkov radiation, which resembles a sonic boom or the bow wave of a boat passing through water. Using an array of four 11-m gamma-ray telescopes, HESS can take stereo photographs of these light flashes, achieving a focus about 50 times better than that of the CGRO2. HESS discoveries Supernova shapes
The focus of HESS is sharp enough to reveal the outline or boundary of the source, indicating
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A fuller Milky Way
Before HESS, only a few very-high-energy gamma-ray sources had been seen by groundbased gamma-ray telescopes. In 2005, HESS discovered whole populations of them in the Milky Way. They had two remarkable features: first, all the sources, except one, are resolved and appear to be nebulous; second, we found that all of them lie more or less in a straight line along the dark lane of our Milky Way. Why? Because they are relatively young (less than about 50 000 years old) and, therefore, still near their birthplaces – in those molecular clouds between the stars consisting of hydrogen molecules, dust particles, and other molecules. The dust particles mixed into these clouds absorb visible light rays to create dark lanes and patches in the Milky Way (you can observe them clearly in the winter night sky from areas in southern Africa that are unpolluted by light). It’s the much older optical stars near to us that create what we recognize as our thick Milky Way. The same molecular clouds also give birth to rapidly rotating neutron stars (or pulsars). By the time it’s about 10 000 years old, a neutron star has already pushed a large halo of ultra-
2. The angular resolution of HESS is a few arc minutes (one arcminute is one-sixtieth of a degree). The best resolution that CGRO can reach is one degree. 3. Cosmic rays: atomic and subatomic particles travelling through space at close to the speed of light. Protons (hydrogen nuclei) form about 90% of cosmic rays, and alpha particles (helium nuclei) most of the rest. Austrian-American physicist Victor Francis Hess first detected cosmic rays during a balloon flight in 1912. He showed that radiation was always present above 150 m, night and day, and increased with altitude. This meant it could not come from the Sun, but had cosmic origins, hence the name ‘cosmic rays’. The discovery won him the Nobel prize for physics in 1936.
high-energy electrons and positrons into the interstellar medium. These electrons boost relic cosmic microwave background photons4 (that is, light that permeates our own Galaxy and the rest of the Universe), created during the original Big Bang, and become very-high-energy gamma rays. The result is the ‘filled’ gamma-ray halo that HESS has revealed. With HESS we’re seeing a new, unexpected gamma-ray reality in the form of many glowing blobs with strange shapes – some looking like shells (supernova remnants), others in the form of filled circles, many shaped like cigars, and even like beans. Perhaps plasma physics, combined with relativistic fluid dynamics, can explain them. Creative spin-offs for industry What’s the practical use of ground-based gammaray astronomy? For telescopes such as HESS to succeed, technological standards have to be pushed to new levels – normally far beyond
The HESS telescopes in Namibia The High Energy Stereoscopic System (HESS) of telescopes, inaugurated in September 2004, comprises four telescopes with superior focus and sensitivity. It is located about 100 km south of Windhoek, Namibia, where the water vapour content is low enough for Cherenkov showers to be seen clearly. The centre of the Milky Way passes vertically over the HESS site, which has enabled the discovery of a diffuse glow of gamma rays from the region near the supermassive black hole at the Galactic Centre. HESS is run by the transnational HESS Collaboration (comprising institutes in Germany, France, the UK, the Republic of Ireland, Armenia, the Czech Republic, South Africa, and Namibia). Northern-hemisphere institutions have entered the partnership because it’s in the southern hemisphere that we see most of the Milky Way. Firsts from HESS HESS was the first telescope to ■ detect a population of very-high-energy gamma-ray sources along the Milky Way ■ offer direct proof that cosmic rays are accelerated (produced) in the shell of a supernova remnant ■ provide a resolved image of a rotationally-induced jet in gamma rays ■ detect a Fanaroff-Riley galaxy* in very-high-energy gamma rays. * This is an active galaxy in which the jet from the central black hole does not point to Earth. It was named after Bernie Fanaroff, who was Director-General in the office of former president Nelson Mandela and who now heads the KAT radio telescope project (see p. 28).
Left: A 60º strip in galactic longitude of our Milky Way, centred on the Galactic Centre as seen in the visible spectrum (optical – above) and by HESS (gamma ray – below). The gamma-ray dot in the centre is spatially coincident with the supermassive black hole at the centre of the Milky Way (which has a mass of 2 million times the mass of our Sun). The brightest gamma-ray source (shelllike) on the right-hand side is the supernova shell shown in the image on the previous page. The gamma-ray sources lie along a narrow straight line, while the visible (optical) stars lie along the broad band that defines the familiar shape of our Milky Way.
industrial standards. Here are two examples. ■ In 1999, we developed a patent for the world’s fastest switching power MOSFETS (metal oxide semiconductor field effect transistors). Financial constraints had forced us to find inexpensive ways to simulate Cerenkov pulses in a Potchefstroom laboratory so as to test the performance of the detectors used on gammaray telescopes. But the world’s fastest MOSFETs were too slow to reach the speed of a Cerenkov light flash, so we changed the architecture of this electronic device to make it about 40 times faster than that being used in industry. MOSFETs are used in electronic switching devices – for example, in electronic power supplies. The switching times (turn-on delay time plus rise time) of state-of-the-art MOSFETs are all longer than 40 nanoseconds (one nanosecond is one billionth of a second). Now our patent can modify a MOSFET to reach a switching time of just a single nanosecond. Faster switching time reduces some of our power needs – in compact ozone generators for automatic dish-washers, for example (reducing the amount of soap we need and giving a more efficient washing cycle), and better-timed spark plugs for motor cars (resulting in less energy waste, more efficient ignition, and better fuel consumption). ■ In 2005, we patented an ultra-fast perfect hardware random number generator. Originally designed to simulate searches for very-high-energy gamma rays from rotating
neutron stars in data dominated by noise, it can now be applied at the microchip level in more down-to-earth ways. It’s useful in scientific Monte Carlo simulation studies (this is like tossing a coin extremely fast at least a billion times to get a sequence of random numbers), for example, and in mathematical models for financial instruments (for example, to calculate risks associated with (For more visit http://arxiv.org/abs/astrothe stock market, which is affected by so many ph/0510397.) factors that a random process is needed to Sources: Optical: Axel Mellinger (http://canopus.physik.unipotsdam.de/~axm/astrophot.html), gamma-ray: HESS describe the future of a stock). Collaboration. Published in Science, vol. 307 (2005), p.1938. It’s also useful in gaming, in computer graphics, and in many security applications. Each time you restart a simple game like Space Invaders, microchips based on this patent could provide a different number sequence; for foolproof security, they could generate a sequence of random numbers that can’t ever be guessed, even with continued surveillance of the system5. Whoever thought that astronomy couldn’t be a down-to-earth discipline? ■ Professor de Jager is based in Potchefstroom at the Unit for Space Physics, North-West University. He is the HESS group leader for South Africa, and is active in the identification, interpretation, and mathematical modelling of HESS sources. For more on the HESS discoveries and for a listing of the ‘source of the month’, visit www.mpi-hd.mpg.de/hfm/HESS/; you will find the HESS inauguration site at http://hess.puk.ac.za and the HESS Source Catalog at www.mpi-hd.mpg.de/hfm/HESS/ public/HESS_catalog.htm.
4. Relic cosmic microwave background photons: this light had a much hotter colour just after the creation of the Universe, but has cooled down sufficiently for detection in the microwave range. 5. Two of our inventions came in the top 12 in South Africa’s 2004 National Innovation Fund Competition, with one (the intelligent spark plug for cars) winning overall second place.
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s part of the ambitious Square Kilometre Array (SKA) international collaborative project in radio astronomy (see box on opposite page), a science demonstrator radio telescope called the Karoo Array Telescope (KAT)1 is being built in the Karoo in the Northern Cape province. KAT is a scaled-down version of the SKA (covering about 1% of the projected 1 km2 of the SKA collecting area). Phase 1 involves constructing a prototype telescope at the Hartebeesthoek Radio Astronomy Observatory (HartRAO) in Gauteng (for completion in 2007) to test the technology. Phase 2 involves constructing the full KAT, with completion envisaged in 2009.
What is KAT? The KAT radio telescope will comprise 20 parabolic antennas, each 15 m in diameter, giving a total of some 3 500 m2 of collecting area. The antennas will have digital Focal Plane Array (FPA) feed systems, a very new technology being developed jointly by South African, British, European, Australian, and American researchers. FPAs break with common radio astronomy practice by using a large interconnected array of receiving elements instead of just one or a few isolated ones. This allows scientists to synthesize multiple simultaneous beams over a wide field of view by combining the outputs from each feed element, using sophisticated digital signal processors. It has the advantage of receiving more beams, which can be read simultaneously, and allowing researchers to ‘see’ more of the sky at any one time. The technique effectively increases the usefulness of the telescope by a factor of about 40. What will it do? KAT will have approximately the same collecting area as the largest radio telescope currently in operation in the southern hemisphere, Australia’s Parkes telescope. KAT’s far larger field of view and its ability to work with many beams simultaneously will allow it to survey the sky much faster than the Parkes telescope; its ability to conduct four or more different experiments simultaneously will further increase its effectiveness. Radio telescopes have the unique ability to ‘re-use’ the received signal for multiple purposes. Operating in the frequency range from 700 MHz to 1.8 GHz, KAT will complement the frequency coverage of the existing 26-m diameter radio telescope at HartRAO. This will
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Kim de Boer explains the potential of South Africa’s new radio telescope concept. significantly extend the range of scientific programmes that South African astronomers can conduct. The overlap in operating frequency range between KAT and HartRAO will, in addition, strengthen the observatory’s existing OH maser research programmes, and the high spectral resolutions, increased survey speed, and widened field of view will mean greater opportunities to image, monitor, and search for OH masers and megamasers2. Finding the right location Only in special site conditions can KAT produce good science. It needs to: ■ be far from cities and people whose appliances emit radio waves in frequencies that interfere with (or ‘pollute’) the KAT’s observations (for example, radios, cell phones, microwave ovens, and television sets) ■ be surrounded by hills or mountains that shield it from radio frequency interference
■ have a maximum baseline of about 1 km (that is, a flat site of about 1.5 km2) ■ enjoy a mild, dry climate, with little water vapour in the atmosphere, low winds, and moderate temperature fluctuations. An excellent site exists in the area between Fraserburg, Williston, and Carnarvon in the Karoo. It lies within 50 km of the anticipated main SKA reference site and close enough to good infrastructure (such as electricity, roads, and an optical fibre telecommunications network) to keep construction and operating costs low. Sparsely populated, and spanning some 40% of the country’s surface, the area has few towns and only 2% of South Africa’s population, so there is relatively little radio interference, despite FM, television, and cell phone towers. It is also a low-rainfall area, with an average of only about 235 mm a year.
1. KAT is being built by South Africa’s Department of Science and Technology, with the National Research Foundation. KAT’s research and development, design, and construction is an international effort led by a South African team. Contributions come from an international group of astronomers and engineers (from universities and industry in the UK, Australia, the Netherlands, Germany, and the USA), who plan to develop the telescope’s cutting-edge technologies. 2. Masers, OH masers, and megamasers: in a maser (acronym for ‘microwave amplification by stimulated emission of radiation’ and the microwave equivalent of a laser), radiation at a certain frequency causes excited atoms, ions, or molecules of a gas to emit further radiation in the same direction and at the same wavelength, which results in amplification. Radio astronomers study naturally occurring cosmic maser sources. OH masers (found, amongst others, in star-forming regions and in comets) are maser sources in which the hydroxyl (OH) molecule is excited to maser action. A megamaser is an extremely powerful maser source, found in the nucleus of an active galaxy. Megamasers can be more than a million times as powerful as maser sources within our Galaxy.
Left: A LandSAT image (satellite photograph) of the KAT site in the Karoo. The dotted line represents the railway line. The hills will screen the telescope from radio frequency interference.
Scientific possibilities The new technology will add significantly to South Africa’s astronomical geographic advantage and offer local scientists greater opportunities for cutting-edge science and collaborations with the world’s leading astronomers. In the area of magnetic fields, for instance, KAT will be able to measure the polarization of radio waves and map the magnetic field among the stars towards galactic and extragalactic point sources. Here are some more of the possibilities that lie ahead. Pulsars
A pulsar is a spinning neutron star that emits energy along its axis of rotation. This energy is received as pulses at radio frequencies (and sometimes in other energy bands) as the star spins, so, in a way, the pulsar acts like a lighthouse. KAT’s multibeaming capabilities permit it to monitor up to 50 pulsars at a time, allowing scientists to search for and detect elusive gravitational wave signatures in pulsar timing data – which, in turn, will help them to test, in more depth, Einstein’s theory of general relativity, and to explain further the nature of space and time. Correlation studies with data from the GLAST satellite (to be launched by NASA in late 2005) will help to confirm the association of gamma-ray sources with pulsars and other astronomical objects (see HESS p. 25), and KAT’s high survey speeds will allow South African scientists to embark on a world-class pulsarsearching programme. They hope that KAT will discover not only the fastest, slowest, strongest, and weakest pulsars and pulsar systems, but possibly even examples of a pulsar orbiting a black hole in a binary system.
or many days (such as those thought to accompany high-energy gamma-ray bursts), and even signals from extraterrestrial intelligence. The telescope’s ability to conduct wide area and directed searches simultaneously will allow investigations of unexplored areas of the transient parameter space – and, possibly, lead to the discovery of new classes of astrophysical objects and events. Galaxy evolution, cosmology, dark matter, and dark energy
One of the most remarkable astronomical discoveries of recent years is that only 4% of the Universe comprises baryonic matter (that is, identifiable elementary particles, such as protons and electrons – the matter of which we are made!). The rest is dark matter and dark energy. Dark matter, as yet unseen, is known to be Bidding for the SKA
South Africa is bidding to host the Square Kilometre Array (SKA) with partner countries Botswana, Namibia, Mozambique, Mauritius, Madagascar, Kenya, and Ghana (in competition with Australia, China, and Argentina). If South Africa’s bid succeeds, a concentration of telescopes will be built (approximately 2 500 in the Northern Cape and about 4 000 in total), opening up into a 5-spiral-arm array into the other provinces and partner countries, with four stations in Botswana, three in Namibia, and one each in the other countries. Proposals from the bidding countries will be submitted by 31 December 2005. They will be evaluated during 2006 on the basis of scientific, technological, and cost criteria, and a decision is expected by 2008.
Right: Artist’s impression of some of the antenna concepts for the SKA. Image courtesy of the International SKA Steering Committee
Universe through the observation of the distribution of nature’s abundant and fundamental element – neutral hydrogen (HI). It will also allow the study of galaxies and clouds of HI far out in the Universe (and, therefore, early in its history), and greater understanding of how the Universe and the galaxies and clusters of galaxies have evolved. ■
A ‘transient’ is a an astronomical event in which the detected emission of radio energy from a target source increases or decreases unpredictably, and in which the timescales of such changes range from milliseconds to months. KAT’s real-time monitoring system will be able to detect short-duration transient events lasting as little as a couple of milliseconds (such as giant pulses from pulsars in distant galaxies)
present because astronomers have observed its gravitational effect. Dark energy is a hypothetical form of energy, permeating all of space, which has been proposed to account for the accelerating expansion of the Universe. The properties of dark matter and dark energy govern the evolution of the Universe and the formation of large-scale structures such as galaxies and clusters of galaxies. They are key parameters in cosmological theories that attempt to explain the nature of the Universe. Recent astronomical advances and more accurate measurements of cosmological parameters have turned observational cosmology into a more exact science. KAT will give new, important experimental potential to this rapidly growing field. It will offer information about the structure of the
Above: The Crab Nebula with the Crab Pulsar at its heart. This pulsar is one of the youngest we know (born in the supernova of AD 1054) and was discovered at radio wavelengths in 1968. More than 1 000 pulsars have been catalogued since the first pulsar discovery in 1967, but there are an estimated 100 000 of them in the Milky Way.
Kim de Boer is the SKA Project Planning Manager. Additional contributions to this article came from the SKA and KAT Project Scientist, Professor Justin Jonas; the KAT Project Manager, Anita Loots; and KAT and SKA Assistant Project Scientist, Dr Adrian Tiplady.
For more information visit www.ska.ac.za; www.skatelescope.org; and www.hartrao.ac.za.
Picture courtesy of NASA
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Dry-season fires in Mozambique Above: This image of coastal Mozambique, taken on 16 August 2005, shows hundreds of fires (marked in red), detected by MODIS* as it passed overhead. White cloud cover is visible at the top and to the left of the image, while wave activity shows up as white along the coastline. Mozambique’s wet season extends from November to April and the weather is dry from May to October. Fires increase in number, size, and intensity as the dry season progresses. A few start naturally, but most are started by people, either intentionally for agricultural purposes or accidentally. Though intentional agricultural fires are not necessarily immediately hazardous, they can damage human health and natural resources. (This image has a spatial resolution of 250 metres per pixel.) * Moderate Resolution Imaging Spectroradiometer NASA image courtesy of the MODIS Rapid Response Team, Goddard Space Flight Center
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Helmut Neumann explains the workings and uses of Earth observation. arth observation is the science – and the art – of collecting information about the Earth’s surface by sensing (or, receiving signals). Conducted over distance, without direct physical contact with the surface, Earth observation is often called ‘remote sensing’. The process is based on the fact that targets of interest (such as fires, vegetation, bodies of water, and man-made structures) scatter, reflect, or emit energy. Sensors, attuned to different types of radiation, are positioned to recognize, receive, and record signals from a target of interest. The information is recorded, processed, and analysed, using data from different sensors. (Some sensors pick up optical signals from the visible part of the electromagnetic spectrum, while others may be attuned to infrared or microwave or radio signals, for instance.) Earth observation images from satellites orbiting our planet offer well-known (and often beautiful) examples of remote sensing. But how does an image reach the Earth from a satellite? How do we receive what the satellite sensors record? Satellite coverage A veritable ‘constellation’ of observation satellites image the Earth daily. Built and launched by international agencies, they carry special imaging sensors, which use different parts
of the electromagnetic spectrum. The spacecraft follow a ‘near-polar’ orbit, missing the Earth’s poles by several degrees. This allows each one to cover most of the Earth’s surface over a given period of time (which can be as short as about 18 days). Orbit segments from north to south are called ‘descending’, while those from south to north are called ‘ascending’. Many of these satellite orbits are also Sunsynchronous, covering an area of the world at a constant local time called ‘local Sun time’. (One, for instance, may pass over South Africa at, say, noon each day.) At any given latitude, as the satellite passes overhead, the position of the Sun View of the International Space Station. It is located in the same low-Earth orbit as satellites used for remote sensing (about 360 km above the planet’s surface). Picture courtesy of NASA
Wide area monitoring The CSIR Satellite Applications Centre (SAC) has developed a wide-area monitoring information system (WAMIS)* as a source of basic satellitederived data, products, and services, to address the needs of users in southern Africa and to support sustainable development. Fires are a high priority in the SADC region and Madagascar, for instance, and WAMIS offers an early warning system for fire potential and detection in the area. The Centre’s advanced fire warning system (AFIS) for southern Africa is based on technology used at the University of Maryland and by NASA, the US space agency. Using data from the MODIS sensor on the Terra and Aqua satellites (NASA) and the Meteosat Second Generation sensor on the EumetSat satellite (of the European Space Agency), fire locations are determined using sophisticated computations and then displayed on regional maps. A short message service (SMS) alert system provides rapid warning of fires. * Eskom and South Africa’s Department of Agriculture contributed to the system’s development.
Left: The CSIR Satellite Applications Centre’s reception station is located at 25°S (at Hartebeesthoek) and its circular footprint covers an area with an approximate range from the Equator to just over 50°S, and in longitutde from 0° to just under 30°E.
1. Minister of Science and Technology, Mosibudi Mangena, has announced a three-year, R26-million project to develop space science and launch South Africa’s second satellite in 2006. 2. In the horizontal coordinate system, azimuth is the horizontal component of a direction (compass direction), normally measured around the horizon from north towards the east (that is, clockwise) and measured in degrees. The other component is elevation above the horizon (or, altitude).
Helmut Neumann is Manager: Earth Observation Data Centre, CSIR Satellite Applications Centre. For more on remote sensing, visit the Canada Center for Remote Sensing at www.ccrs.nrcan.gc.ca. For details of the CSIR SAC fire information system, consult SAC News (October 2004), available online at www.csir.co.za/sac. The booklet, Let’s Learn about Space and Satellites (CSIR Satellite Applications Centre) is available on request from CSIR Communication, tel. (012) 841 3887. You’ll find a useful encyclopedia at www.wikipedia.org.
Gathering and using the data Observation satellites use approximately 8.02–8.4 GHz of the X-band for feeding data down to Earth (see electromagnetic spectrum diagram, right). These ‘raw’ or ‘signal’ data (in the form of a binary stream of noughts and ones) are used to produce the images. At the CSIR SAC, data are received by antennas that need to track a satellite continuously as it passes through the footprint. Ephemeris data (that is, tables of the predicted location of the satellite) are consulted, and then, using azimuth and elevation, the antenna is aimed at the expected location of the satellite as it appears over the horizon2. A computer moves the antenna (following the predicted orbit of the satellite), searches for its X-band transmission and, if a strong enough signal is detected, the computer
uses it to track the satellite. (Without a Wavelength (m) Frequency (HZ) Lower Longer strong signal, the ground station cannot receive data from the satellite.) 1KHz 104 104 The original X-band data at 1 km ➔ 106 1MHz approximately 8 GHz are received and 102 RADARSAT converted by ‘downconverters’, located 1 m ➔ 1.0 109 1GHz SAR within the antenna, to an intermediate 10 5.3 Ghz 1 cm ➔ 10 10-2 frequency of 375 MHz. The intermediate 5.66 cm 12 1THz 10 -4 10 data are then converted into two different SPOT HRV 1014 1 m ➔ data streams (data and clock synchro10-6 0.5–0.89 m 1PHz 16 nization) by a ‘bit-synchronizer’ within the 10 10-8 1 nm ➔ Centre’s computer facility. Digital recording 1018 1EHz 10-10 systems store the resulting information, 1020 10-12 from which a frame synchronizer prepares images. After conventional computer © CCRS/CCT Higher Shorter manipulation, the digital image data are Above: The electromagnetic spectrum ranges recorded on CD or DVD. from the shorter wavelengths (including gammaHigh-resolution images are generated and X-rays) to the longer wavelengths (including from data supplied by satellites such as microwaves and broadcast radio waves). Several Quickbird or Spot 5. Applications include regions of the electromagnetic spectrum are urban development and security, which useful for remote sensing. require fine spatial resolution (that is, How satellites send discernible detail in the image). their data Medium-resolution images come from sensors on board satellites such as Landsat and Spot 2 and Remote sensing satellites are in low 4, and are used for disaster monitoring and Earth orbit at 200–1 200 km above the planet’s surface. Some circle the management. The wide area coverage and/or whole Earth in about an hour and a frequent revisit times make them ideal, for example, for monitoring fires, marine phenomena, half. A commercial remote sensing satellite weighs approximately 955 kg changing demographics, crop yields, and and is about 3 m long. droughts, and for mapping land cover. Data acquired by satellites are Low-resolution images (generated from the transmitted in three main ways to the MODIS and NOAA series of satellites) are useful Earth’s surface. If a ground receiving in meteorology and environmental monitoring. station (GRS) is in the satellite’s line Their sensors can pick up the temperature of the of sight, data can be transmitted sea and land, clouds and precipitation, winds, sea directly. If not, the data can be recorded on board the satellite for levels, ice cover, vegetation, and gases. ■ ➔
in the sky is the same in the same season. This ensures consistent illumination conditions when acquiring images in a specific season over successive years, or over a particular area during a series of days. This is important for monitoring changes among images or for ‘mosaicking’ adjacent images (that is, putting them together in a pattern or a sequence), as they do not have to be corrected for differing lighting conditions. If, in addition, the orbit is Sun-synchronous, the ascending pass is most likely on the shadowed side of the Earth while the descending pass is on the sunlit side. Sensors that record reflected solar energy image the surface on a descending pass, when solar illumination is available. Passive sensors recording emitted radiation (thermal radiation, for instance) can also image the surface on ascending passes. The CSIR Satellite Applications Centre (SAC) has agreements with international organizations, such as the United States Geological Survey and the French Spotimage, to receive data from sensors aboard their satellites when they are in the Centre’s ‘footprint’ (or, range of data reception) over southern Africa1. Transmission of data to the receiving station occurs only when a satellite is within this footprint.
later transmission to a GRS. Data can also be relayed to the GRS through the tracking and data relay satellite system of observation satellites (a series of communication satellites in geosynchronous orbit); the information is transmitted from one satellite to another till it reaches the appropriate GRS.
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What is a hurricane? ‘Hurricane’ is a regional term for what’s called in the scientific literature a ‘tropical cyclone’ (or, revolving storm). It’s the same weather system that in some parts of the world is also called a typhoon1. A tropical cyclone is a very intense low air-pressure system that develops over warm tropical and subtropical waters into an upward spiral of fast-moving air and moisture. Storms are normally classified as tropical cyclones when their winds reach 118 km/hr. Their violence makes them among the most damaging weather systems on Earth. They cause devastation by their very high winds, by flooding associated with high rainfall, and by storm surges along the coast. At the centre of a cyclone is a calm area called the ‘eye’, where atmospheric pressures are at their lowest – usually below 900 hectopascals (hpa) (in contrast with normal sea-level atmospheric pressure, which is 1 013 hpa). Wind speeds of some 350 km/hr have been measured in northern Pacific typhoons; the highest recorded rainfalls associated with tropical cyclones are in the region of 3–5 m (that is, 3 000–5 000 mm) on the Indian Ocean island of Reunion. Individual tropical cyclones have names
Above: Unusual panoramic side-view of the eye of Hurricane Emily from the International Space Station on 16 July 2005 as it passed over the southern Gulf of Mexico looking eastward toward the rising Moon. The eye appears as a depression in the cloud deck that stretches out to the horizon. At the time, Emily was a strengthening Category 4 hurricane with wind speeds approaching 250 km/hr. The 2005 Atlantic hurricane season had a record-breaking start. Hurricane Dennis became the first Atlantic hurricane to reach Category 4 strength in July (in the past, such strong storms haven’t formed so early in the season). A few weeks later, Hurricane Emily superseded Dennis as the most powerful pre-August storm on record; 2005 was the first season that had two Category 4 storms before the end of July. Astronaut photograph ISS011-E-10509 (acquired with a Kodak 760C digital camera with a 400 mm lens) comes from the ISS Crew Earth Observations experiment and the Image Science & Analysis Group, Johnson Space Center. The International Space Station Program helps astronauts take pictures of Earth that will be of value to scientists and the public, and that are freely available on the Internet. For more, see the NASA/JSC Gateway to Astronaut Photography of Earth.
to identify them for purposes of research, communication, and record-keeping. The names are set ahead of each season and allocated alphabetically as a new storm begins. In each of the world’s different tropical cyclone systems, the name of the season’s first tropical cyclone begins with the first letter of the alphabet, and subsequent storms start with the next letter, down the alphabet from A to Z. This year, for instance, in the North Atlantic system, three cyclones causing exceptional damage were Katrina (which devastated New Orleans), followed by Rita, and then Wilma. Our Southern Indian Ocean System has its own alphabetical sequence. Where do tropical cyclones occur? To develop, tropical cyclones need moisture, heat, and rotation, so they tend to occur in tropical areas where sea
At what time of year can we expect them? Tropical cyclones normally develop in the latter part of summer, when sea temperatures have had the longest possible time to warm up. So, in the northern hemisphere, typhoon and hurricane
1. ‘Hurricane’ and ‘typhoon’ are regionally specific names for a tropical cyclone – ‘hurricane’ via Spanish hurácan (from the American Indian Tain word hurákan, or hura meaning ‘wind’); ‘typhoon’ from the Chinese tai fung meaning ‘great wind’ and influenced by the Greek tuphon meaning ‘whirlwind’.
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temperatures are warmest. Within 5° latitude of the equator, however, there is insufficient Coriolis force (that is, the force caused by the Earth spinning on its axis) for rotation to be strong enough. The cyclones form in a belt of westward moving winds (Easterlies) in the tropics and subtropics of both hemispheres. Areas of the Earth most affected by tropical cyclones are those in and around the Caribbean; Japan, Taiwan, China, Korea, and adjacent areas in Asia; the tropical Pacific Islands; Northern Australia; and the Indian Ocean islands.
Q Your Q UEST ions answered The devastating Atlantic hurricane season of 2005 wreaked havoc in the USA. What are these fierce storms? Can they cause similar destruction in South Africa? Is global warming responsible? Ian Meiklejohn answers these and other questions. seasons are usually between August and the end of October, and in the southern hemisphere between January and March.
Africa in 2000 was caused by two tropical cyclones that passed further over the warm land than normal.
How do they form? Several conditions have to be present for tropical cyclones to develop: ■ they grow out of an existing lowpressure weather system that has sufficient rotation and uplift ■ they’re driven mainly by heat and moisture ■ their energy comes from warm sea temperatures (normally over 26°C) and from the latent heat that’s released as the water vapour derived from evaporation of sea-water condenses. Following the principle that warm air rises, a tropical cyclone develops when the atmosphere up into which the rotating spiral of warm moist air is moving, cools rapidly with altitude (at a rate greater than 10°C per kilometre above the Earth’s surface) – in other words, when the atmosphere is ‘unstable’. Then, with sufficient moisture, clouds form as the air rises, cools, and reaches dew-point. In addition, there need to be nearuniform winds at the different levels of the Earth’s atmosphere between the surface and upper levels, to prevent the developing tropical cyclone from being disrupted (in other words, the vertical wind shear between the surface and upper levels of the atmosphere must be low).
Is global warming causing more tropical cyclones? There is no conclusive evidence for this, and, globally, the number of tropical cyclones has remained fairly constant. But some atmospheric models indicate that the number and intensity of tropical cyclones may increase on account of continued global warming and rising sea temperatures. ■
How do they dissipate? They dissipate when the system can no longer maintain itself, that is, when the strong vortex at the centre of a tropical cyclone is destroyed, when the moisture level falls, or when heat is removed. Normally, when such a storm moves over
Professor Meiklejohn is in the Department of Geography, Geoinformatics and Meteorology, University of Pretoria.
land that is cooler than the warm sea, heat is lost; also, the land’s frictional forces weaken the vortex and help to dissipate it. Some oceanic islands are too small for their frictional forces to weaken tropical cyclones, so these islands are often devastated. Do they affect South Africa? Tropical cyclones are infrequent in South Africa – and they affect only the northern parts of the South African coastline, where sea temperatures in summer are high enough. Furthermore, the island of Madagascar is thought to act as a buffer, stopping tropical cyclones from reaching the southern African coast. Mozambique and the Indian Ocean islands are far more vulnerable because they are further north. In 1984, cyclones Domoina and Imboya devastated northern parts of KwaZulu-Natal, and the flooding in Mozambique and northern South
For more, visit the US National Hurricane Center at www.nhc.noaa.gov; the Joint Typhoon Warning Center at www.npmac.navy.mil/jtwc.html; Eumetsat at www.eumetsat.int; and Natural Hazards, Earth Observatory at http://earth observatory.nasa.gov/NaturalHazards/.
Above left: Satellite image of Tropical Cyclone Guillaume to the east of the Indian Ocean island of Reunion (with Mauritius to the west of the system). Image Courtesy of Jacques Descloitres, MODIS Land Rapid Response Team at NASA Goddard Space Flight Center, via the Earth Observatory, NASA.
Below left: Global sea temperatures in midSeptember 2005. The orange and yellow areas show the regions in the northern hemisphere where sea temperatures were warm enough for tropical cyclones to develop at that time of year. During the southern hemisphere summer, the belt of warm water moves south, creating a new, southern region in which tropical cyclones can develop. Image: Courtesy of The Earth Observatory, NASA
Below: The path of Hurricane Isabel in 2003 developing and intensifying from the West African coast across the North Atlantic. It caused considerable damage in the southeastern USA. Image courtesy of Eumetsat Sept 15 Sept 13 Sept 11 Sept 09 Sept 08 Sept 07 Sept 05 Sept 03
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David Block goes in search of cosmic dust. ur majestic Milky Way Galaxy spawns some 100 thousand million stars, giving it its awesome ‘milk-like’ appearance and its name. But these stars are not uniformly spread across the sky; there appear to be innumerable holes or voids. Do these mark an absence of stars, or the presence of ‘cosmic smoke’ or dust? We now understand that those dark lanes in our Milky Way are filled with extremely small, solid particles of dust. Cosmic dust pioneer Mayo Greenberg likened them to smoke particles: they are approximately the same size as those exhaled by a cigarette smoker. The light from a light bulb across a smoke-filled room looks noticeably dimmer than in a room with clear air. This dimming is caused by exactly the same phenomenon as the dimming of the light of distant stars. Each smoke particle, whether in a smoky room on Earth or lurking in the space between stars (interstellar space), diverts the light that hits it – by scattering it in other directions, or by absorbing it, or by a combination of both1.
Cold icy grains Grains of cosmic dust in our Milky Way Galaxy can be very cold: a mere few degrees above absolute zero! Interstellar dust grains are produced in the atmospheres of cool old stars. Minute sub-micron rock-like particles (called silicates) are blown from these atmospheres into surrounding space. They move away from their parent
stars, and because of their great distance from all stellar radiation, drop to temperatures as low as 260°C. Herein lies the marvel: they are so cold that any ion, molecule, or atom from surrounding gases sticks to them. Amazing chemical evolution may occur on the surfaces of these ice mantles. Just as water vapour forms frost on the inside of windows on a cold winter’s day, these tiny silicate grains accrete mantles of frozen water, methane, ammonia, carbon monoxide (and many other molecules). When these mantles are exposed to the ultraviolet radiation from neighbouring stars, simple molecules gradually convert into more complex ones until, eventually, many prebiotic molecules (such as amino acids) are manufactured. So every person in the world is made of cosmic stardust!
In other galaxies too Whereas the presence of cold cosmic dust grains in our Galaxy was accepted, their ubiquity in distant galaxies had yet to be conclusively demonstrated. In the early 1990s, I was privileged in the Atacama desert in Chile to spearhead an international collaboration to determine the presence of gargantuan veils (or masks) of cold and very cold cosmic dust, often spanning 100 000 light years or more, in galaxies beyond the Milky Way. Once masks of cosmic dust are penetrated with special near-infrared cameras (which allow us to view the Universe not optically, but with near-
Above: Dense clouds of cosmic dust seen in the form of cometary globules with dark heads and long flowing tails. Photograph: David Block in Chile, South America
infrared ‘eyes’), galaxies look supremely different. With these cameras, the central regions of spiral galaxies often betray magnificent, elongated starry bar-like features, many of which are obscured optically by dust. Our work proved that astronomers had missed nearly 90% of the dust masses in external galaxies. Furthermore, our team discovered that galaxies are not dynamically ‘closed’ systems but ‘open’ ones, continually accreting gas in their outer parts and as much as doubling their masses during the age of the Universe. Last year we discovered a huge ring of carbon stars in the outer regions of the Triangulum spiral galaxy M33, over 2.5 million light years distant. The ring is some 30 000 light years in diameter. We believe that this ring, too, is the signature of fresh gas accretion. How encouraging that the journal Nature featured our work on two covers, and that we have conducted this research, for nearly 20 years, on South African soil. ■ Professor Block is Director of the Anglo American Cosmic Dust Laboratory at Wits. He is well known for his success in introducing the public to the marvels of astronomy. He is also involved in the University of the Witwatersrand’s National Astronomy Outreach to school learners in conjunction with the TISO Foundation, Kagiso Exhibitions, and Pick’nPay.
1. Our sky is blue because of the scattering of short-wavelength blue photons by particles of gas and dust in our atmosphere.
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The discovery of the nearest star to the Solar System was made in South Africa, writes Ian Glass. hat makes deep thinkers and dawdlers get on with their work? The fear that someone else might get the credit, in many cases. But it still took 250 years for anybody to discover which star is our nearest neighbour. It all started with Copernicus, in 1543 – and even he published his theory not long before he died later that year. Ever since he proposed that the Earth is in orbit around the Sun and not the other way around, people have realized that the nearest stars ought to show the effect called parallax. Parallax is what you see if you hold a pencil at arm’s length and look at a distant object while moving your head from side to side. The pencil seems to move back and forth against the background. Think of your head’s movement as the Earth’s orbit, the pencil as a nearby star and the background as the distant stars. Yet astronomers had never seen this effect. Either Copernicus was wrong or the stars had to be unimaginably far away from us. Of course, the second explanation was the correct one. But it wasn’t until the 19th century that astronomical instruments were precise enough to detect parallax, and thus the nearest star. And it happened in South Africa – not once, but twice.
Alpha Centauri The man who made the first measurements showing parallax – in 1832–33 – was a former lawyer and the second director of the Royal Observatory at the Cape of Good Hope, Thomas Henderson. The bright double star he chose, Alpha Centauri, was the nearest known until 1917, when a third, slightly closer, member of the same system was found by Richard Innes at the Union
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Observatory in Johannesburg. What made Henderson concentrate on Alpha Centauri? There is another effect that gives away the presence of a nearby star, called ‘proper motion’. A nearby moving object will cross our field of view more quickly than a distant one, as you can see if you compare the flight of a nearby bird with that of a distant aeroplane. The English astronomer Edmund Halley, of comet fame, had noticed in as early as 1710 that some bright stars had moved in relation to the others. This suggested that they were closer and might be good candidates for parallax work. But measuring the parallax of a star against the background sky is a highly tedious affair – especially if the facilities where you are working are not up to
Above: The Royal Observatory, Cape of Good Hope, in a photograph of about 1843 by C. Piazzi Smyth (made using an early photographic process called calotype). This is the first photograph of any observatory and one of the oldest surviving photographs in the world. Background sky: From The Midnight Sky, Familiar Notes on the Stars and Planets by Edwin Dunkin (London: Religious Tract Society, 1869), showing the area in which Alpha Centauri may be seen.
feat for the time, since the angle he had measured was about one tenthousandth of a degree!). Pipped to the post, Henderson presented his own results three weeks later, showing the world that Alpha Centauri had a parallax of 1.16 ± 0.11 arcsec (that is, more than three times
Innes’s star, Proxima Centauri, found from Observatory in Johannesburg, continues to hold the record for closeness to us. scratch. Henderson was fed up with the unfinished state of the Cape observatory (no toilets, for example!) and had already resigned when he received a tip-off that Alpha Centauri seemed to have a large proper motion – it might therefore be nearby, and so it proved. During his last month in Cape Town, before returning home to Britain, he redoubled his efforts on Alpha Centauri. That was the last movement on the subject for a while, however. Instead of working up his results as soon as he had finished, Henderson set them aside. It was only in 1838 that he was jolted into action again, when a German called Friedrich Wilhelm Bessel announced his own parallax measurements of 0.31 ± 0.02 seconds of arc (arcsec) for a star called 61 Cygnus (a formidable technological
that of Bessel’s star) and is therefore less than one third the distance from Earth of 61 Cygnus. He caused a sensation. The results vindicated Copernicus at last, and also allowed distances to the stars to be calculated properly for the first time, using trigonometry. (The diameter of the Earth’s orbit forms one side of a triangle and the other angles are all known.) As the 19th century wore on, more parallaxes were measured, but none exceeded that of Alpha Centauri. Proxima Centauri Enter the 20th century. This time, the breakthrough happened in Johannesburg. Richard Innes, a former liquor merchant, had set up the observatory there in 1903 and later took pictures of the sky using a wideangle photographic telescope. He was
Photographs reproduced courtesy of the SAAO
Q Measuring up Nothing is for ever “Ever since the 1930s, researchers have speculated that the constants may not be constant,” write John D. Barrow and John K. Webb in Scientific American (June 2005). “If the extra dimensions of space were to change in size, the ‘constants’ in our three-dimensional world would change with them.” But it’s hard to tell through experimentation whether this happens, because “the laboratory apparatus itself may be sensitive to changes in the constants. The size of all atoms could be increasing, but if the ruler you are using to measure them is getting longer, too, you would never be able to tell.”
Practise your scales
interested in comparing photographs taken several years apart to see if anything had changed. He hoped to find double stars that were in orbit around one another, as well as stars that had moved or changed in brightness. To do this, he acquired a stereo-comparator instrument made by Zeiss that had been modified so that one could look through an eyepiece and rapidly ‘blink’ between two glass photographic plates. He became one of the first experts on the use of this instrument. In 1915, Innes had the bright idea that Alpha Centauri, as a double system, might have a third member nearby. To check his notion, he spent 40 hours comparing two plates, taken five years apart, of that area of sky. To his delight, he found such a star, rather faint (less than ten-thousandth of the brightness of the brighter member of the double) and far away (over two degrees). It had roughly the same proper motion as the two other members and was therefore likely to be connected with them. Unlike Henderson, Innes published his result immediately and then set about measuring the parallax of the new star (making visual observations against a nearby comparison star using a 9-inch telescope). He was not alone. Apparently unknown to Innes, a Dutch volunteer observer at the Cape, J.G.E.G. Voûte, had read his paper and had included the high proper-motion star on his own photographic parallax programme. Innes was startled to receive a letter from Voûte in April 1917 announcing that he had almost got a parallax for it. Nothing like someone on your heels to get you going. By September, Innes and his assistants W.M. Worsell and H.E. Wood, using Voûte’s work
Above left: R.T.A. Innes, Director of the Union Observatory, Johannesburg. Behind him is the blink comparator he used to make the discovery of Proxima Centauri. Above right: J.G.E.G. Voûte, the Dutch volunteer at the Royal Observatory, who made a determination of the parallax of Proxima Centauri at the same time as Innes (from a group photograph dated 1914).
too, had obtained a precise parallax and published it. Voûte’s result was more accurate and in the combined results it was given three times the weight of Innes’s determination. The mean result they got at the time showed the third star to be slightly closer to us than the other two. Innes modestly named the new star ‘Proxima’ (rather than ‘Innes’s Star’ as some suggested). It is a relatively cool ‘red dwarf’1, though it flares up in brightness from time to time. Modern work has upheld the result that it is the nearest star, at 4.22 light years from us. Its orbit around the other two members takes about a million years. (The closer pair go around each other in about 80 years.) More recently, there have been many searches for even cooler and fainter stars using infrared telescopes and satellites, but without success. Thus Innes’s star, Proxima Centauri, found from Observatory in Johannesburg, continues to hold the record for closeness to us. ■ Dr Glass is a Senior Astronomer at SAAO. He specializes in infrared studies of active galactic nuclei and mass-losing stars, and has a great interest in the history of astronomy. For more information read Patrick Moore and Pete Collins, The Astronomy of Southern Africa (Cape Town: Howard Timmins, 1977) and Brian Warner, Astronomers at the Royal Observatory, Cape of Good Hope (Cape Town: A.A. Balkema, 1979). Visit the historical pages of the Astronomical Society of Southern Africa at www.saao.ac.za/assa/html/ 39_historicalsection.html
■ The Richter Scale was originally devised in 1935 to study a particular area of California. Now it expresses the size of earthquakes everywhere. Wikipedia describes it as “a base-10 logarithmic scale, obtained by calculating the logarithm of the combined horizontal amplitude of the largest displacement from zero on a seismogram.” There are also scales to express the intensity of an earthquake, which depends on local conditions. ■ The time scale used in geology is divided up on the basis of differences between fossils found in different layers. Last year, a new division was added to the scale: the Ediacaran Period, which lasted from 600 million years ago to 542 million years ago. Wikipedia says: “The period is unusual because its beginning is not defined by a change in the fossil record. ... [but] by the appearance of a new texturally and chemically distinctive carbonate layer that indicates a climatic change (the end of a global ice age).” ■ The Kelvin scale refers to “the relationship between temperature and the efficiency of work produced by an engine” (Science Friday). The zero of the scale is absolute zero, the lowest temperature possible in theory, the point at which “a steam engine is completely efficient”. It corresponds to minus 273.15°C and is where molecular movement almost stops.
Extremes in nature ■ How tall can a tree grow? Biologists say about 130 m is the maximum, after which the water drawn up to the top of the tree would not be able to fight gravity. The tallest tree in the world, a Californian redwood, is 112 m tall. ■ The biggest living organism in the world, according to Extreme Science, is a fungus growing in eastern Oregon in the USA. Most of it is underground, but it’s estimated to cover about 890 hectares and be at least 2 400 years old. It belongs to the species Armillaria ostoyae, or honey mushroom. ■ The lowest point on Earth that’s not under seawater is in the Bentley Subglacial Trench, 2 555 m below sea level. It’s in Antarctica, under the thickest ice ever found (almost 4.8 km thick). ■ The lowest temperature ever reported, also in the Antarctic, was minus 89.4°C. The highest on record was 57.8°C, recorded in Libya in 1922 – as measured 1.6 metres above ground, which is cooler than the surface temperature.
Hot stuff The first sealed thermometer was made by Daniel Gabriel Fahrenheit, a German physicist, in 1714. Philadelphianinstrument.com explains that “in making a liquid thermometer, the mercury is ordinarily driven to the top of the tube by heating. The glass is then sealed off, resulting in a vacuum when the mercury contracts during cooling. For high-temperature applications, the tube is filled with a pressurized gas before sealing to prevent the mercury from boiling. Coloured alcohol or other fluids are used for recording temperatures below the freezing point of mercury, which is minus 38.87°C.”
1. Red dwarf: a cool, faint, low-mass star, with a mass and diameter less than half those of the Sun. It is red because of its low surface temperature, and inconspicuous because of its low luminosity. It is the longest-lived and most common type of star.
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Sun and Moon ■ The Sun was a man with a powerful light shining from his armpits who created day by raising his arms. But as he grew old and slept too long, the people grew cold. Children crept up on him and threw him into the sky, where he became round – and there he stays, warm and bright. (Namaqua) ■ Some people believed that the Sun is eaten each night by a crocodile and emerges from the crocodile each morning. (Tswana) ■ Nwedzana is the waxing crescent of the Moon. Horns pointing up when the new crescent was sighted in the evening sky meant it was holding up many diseases; horns pointing down meant it was a basin pouring down illness. (Sotho, Tswana, Venda) ■ Ng’olumhlope namhla (Zulu) was the dark day after the waning crescent disappeared from the sky. Many considered this a solemn day of rest, with no work or business done and no weddings celebrated.
The Milky Way ■ A strong-willed girl was angry when her mother wouldn’t give her any delicious roots, roasting on the fire. She grabbed them and threw them, with the ashes, into the sky. Now the red and white roots glow there as red and white stars, and the ashes are the Milky Way. (KhoiSan) ■ To Xhosas, the Milky Way seemed like the raised bristles on the back of an angry dog. Sotho and Tswana saw it as Molalatladi, the place where lightning rests. It kept the sky from collapsing and showed the movement of time. Some said it turned the Sun to the east.
Orion ■ A girl child of the old people had strong magical powers, turning a group of fierce lions into stars by looking at them. The largest are now in Orion’s belt. (KhoiSan) ■ The Pleiades were the daughters of the sky god. When their husband (Aldebaran) shot his arrow (Orion’s sword) at three zebras (Orion’s belt), it fell short. He dared not return home because he had killed no game, and he dared not retrieve his arrow because the fierce lion (Betelgueuse) sat watching the zebras. He remains there, shivering in the cold night and suffering thirst and hunger. (Namaqua) ■ The stars of Orion’s sword were ‘dintsa le Dikolobe’, three dogs chasing the three pigs of Orion’s belt. Warthogs have their litters while Orion is prominent in the sky – frequently litters of three. (Tswana)
Sky calendar ■ Canopus was called Naka (‘the horn’) or E a dishwa (‘it is carefully watched’). Sotho men camped in the mountains and watched the early morning skies in the south. The first to see the star would prosper that year, with a rich harvest and lifelong good luck. The following day, divining bones were examined in still water to predict the tribe’s luck for the coming year. ■ Among Venda people, the first person to see Nanga (Canopus) in the morning sky announced the discovery by climbing a hill and blowing a sable antelope horn (phalaphala). ■ The shield of the little horn (the Small Magellanic Cloud) is called mo’hora le tlala (‘plenty and famine’). If dry dusty air made it seem dim, famine could be expected. (Sotho) ■ The bright stars of the Pointers and the Southern Cross often seemed like giraffes, which Venda people called Thutlwa (‘rising
Dave Laney shares some s0outhern African traditions. above the trees’). In October, the giraffes would skim above the trees on the evening horizon as a reminder to finish planting. ■ For Swazi and Zulu skywatchers, iNqonqoli or Ingongoni was associated with wildebeest, whose calves were born in the season when Spica rose before the Sun and the morning star. ■ Some people called Canopus the ‘ants’ egg star’ because of its prominence during the season when the eggs were abundant. (Sotho, Swazi, Nguni) ■ isiLimela (the Pleiades) were the ‘digging stars’, whose appearance in southern Africa
meant the coming need to begin hoeing. (Sotho, Swazi, Nguni) ■ Throughout Africa, the Pleiades marked the growing season. Called the rainstars (Khuseti or Khunuseh), their appearance heralds the rains and thus the beginning of a new year. (Khoisan) ■ Dr Laney works at the SAAO in the area of variable stars, clusters, and the cosmic distance scale.
Above: Poster illustrating legends of southern Africa relating to the heavens. Artwork: Braam Botha/Picture courtesy of the SAAO
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Kobus Meiring was responsible for developing and constructing the Southern African Large Telescope (SALT). What project management techniques helped him to succeed with such a tight schedule and budget?
working in parallel, it’s visible when one clear, concise, unambiguous way so people What’s the basis for starting a slips, so others tend to relax too. It’s best to don’t change their minds later. unique project like SALT? have to stick to your schedule whatever After that, develop a high-level system The first step is to find examples of how happens – rather wait for someone than specification to give users what they need – others have constructed something like it, have someone wait for you. for example, a mirror system to do this or so we visited and linked up with other It also pays to put in effort up front. Our that. That way you know exactly what kind telescopes. SALT was lucky to have the small team spent time analysing and of machine you have to build. Hobby-Eberly Telescope (HET) in west specifying – that’s when it’s cheapest to Texas as prototype. They’d done fantastic change things. Once you’ve started cutting groundbreaking work, and were willing to metal it gets expensive. For example, you share their lessons with us. Initially, we Appoint couldn’t build SALT without were just going to copy it, but our site the right people. Good computers. Low-level software was and weather are different so, for written by the suppliers but we practical reasons, that wouldn’t people can make bad things wrote the high-level software inwork. Also, the computing world work; but bad people house and made lots of design changes very quickly, so we kept revisions. We brought in the coding looking for better, long-lasting solutions. can ruin anything. specialists only after two years, when we It helps to be open to suggestions. On knew exactly what we wanted. every topic there was someone who knew Be as sure as possible about what you more than I did – just not the same person Once that’s done, divide the machine, or want before spending money on hardware in each case! – so I had to go out and find whatever you’re building, into logical and metal. It’s sometimes hard to find the that person. Learning lessons is expensive construction sub-systems, small enough that balance, but that comes with experience – – rather get other people to share their one team can take ownership of it. This is you do have to start at some stage! knowledge with you. Look for the gems in crucial! Then find the right team of people their experience that you can learn from. to match this breakdown, and someone What about the people? Having been in the military industry, it who’ll take autonomous charge of each subMy top project management tip is: appoint helped that I had a good idea of what we system – for instance, the mirror, the control the right people. Good people can make could actually get done in South Africa. system, the structure. bad things work; but bad people can ruin We’re very proud that we did so many anything. And in a high-stress My scheduling basis is to plan for success, things locally and didn’t just import environment, have a sense of humour. and to leave some margin. But each subeverything from abroad. system has its own schedule and the margin Have the right team, and make sure What planning principles goes onto the project level as a whole, there’s ownership, in the sense of people do you follow? because you don’t know beforehand where taking full responsibility for their work. For a start, understand what the users want, and what margins you’ll need. Then Then give them the right means (budget, and also what’s out there already. everyone has to plan to do things on time! authority, assistance, whatever’s required!) Reinventing the wheel is a great waste. Managing the margin centrally also fights otherwise they’ll get frustrated and Then formalize the user requirements in a the ‘human nature’ element: with 10 teams demotivated.
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The SALT project had a small core team What was special for you about the of 10 handpicked people. That made it SALT project? relatively straightforward. What worked Coming from the commercial world, I was was that none of us had an astronomical struck by the way people were willing to background (I came from a helicopter share. We could ask anyone for advice project, someone else from earth-moving and they gave it freely. Very refreshing! equipment) so we weren’t scared to ask This is really the way to move intellectual questions – the honeymoon period lasted property around. a long time! Larger numbers of people have more expertise than a small group and it’s foolish not to take New projects advantage of that. I’m a great elsewhere – in the USA and one for asking questions – if Europe – are interested in sometimes you look a bit silly it doesn’t matter, it keeps you the technology we’ve humble. developed Coming from different environments, we brought ideas into this Regarding the construction itself, what project from outside astronomy. With stood out for me was the range of budgets and time so tight, the right magnitudes! We were working on a 10commercial ‘off the shelf’ inputs help a lot storey-high building with steel structures – and our range of specialists from weighing hundreds of tonnes. At the same different backgrounds meant we knew time we were working with mirror where to find what we wanted. Diversity adjustments of less than 50 nanometres. pays! Thinking ‘outside the box’ is what it’s about. For most people, that’s a theoretical measurement – in my previous life, Another thing is to do what you like nanometres belonged to biology, on the doing, and to build the team around what scale of viruses! they like to do. It won’t lead to excellence always to be doing what you don’t like – Here you polish glass to an accuracy of people do better at what they enjoy. But a couple of nanometres, yet it’s open to then nobody must say “that’s not my job”. the environment of night temperature When you’re responsible for the mirror, change. Steel in the structure moves with say, you’ll end up doing things that are temperature all the time, so alignment is tedious because you’ve taken really challenging. Yesterday, for instance, responsibility for the end result. daytime temperature at Sutherland went
up to 30°C then down to 4°C at night – yet you have to keep the mirror aligned to less than 50 nanometres of accuracy! We’re catering for an operational range of 25°C over a 24-hour period here. Then there’s the tracker 13.5 m above the primary mirror – with a mass of five tonnes it weighs the same as a small truck, but has to point to an accuracy of better than 10 micrometres (the thickness of a human hair is 100 micrometres) and be constantly aligned! The HET in west Texas and SALT are the only telescopes worldwide with as many as 91 mirror segments, and, now, we are the more accurate. (The Keck telescope, in Hawaii, has 36 segments.) We’re proud that our positioning is the most precise, at this stage, and that our tracker was built in Stellenbosch, not elsewhere in the world. At SALT, we’ve learnt to align 91 mirrors to this high level of accuracy. New projects elsewhere – in the USA and Europe – are interested the technology we’ve developed, which shows the interactional nature of this kind of effort. It’s this kind of sharing that makes for good progress. ■ Originally from the Cape, Kobus Meiring began his work as SALT Project Manager in July 1999. He had previously been programme manager of the Rooivalk Helicopter Programme in Kempton Park, Gauteng.
Above and below: Stages in the construction of SALT. Pictures courtesy of Phil Charles/SAAO/SALT Foundation
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Q The S&T tourist
To appreciate the cosmos, visit Sutherland – and South Africa’s planetariums. f you can’t yet make the pilgrimage to Sutherland, the Cape Town and Johannesburg planetariums offer the closest possible experience actually to being there. Their brand new SALT presentation (see p. 44) shows visitors just how the SALT telescope works and what it sees.
The planetarium experience
For details, phone the Iziko Planetarium at (021) 481 3900 and the Johannesburg Planetarium at (011) 717 1392.
The southern night skies ■ At Sutherland’s latitude, the Galactic Centre – visible most of the year – passes directly overhead. Packed with billions of stars, it’s a celestial treasure chest. ■ Close to the Southern Cross and Pointers in the sky are Alpha Centauri (our nearest celestial neighbour [see p.36]), Omega Centauri (king of all globular clusters), and the massive erupting star, Eta Carinae. ■ Not far away lie the two Magellanic Clouds, our neighbouring satellite galaxies. ■ Away from the plane of the Milky Way, we peer deep into the cosmos to a Universe distant in both time and space. The great history book of the cosmos is open. We just have to learn to read it. – AF
Sutherland The small rural town of Sutherland, four hours’ drive from Cape Town and close to the SAAO research station on the hill above the town, was founded in 1855. Named after Reverend Henry Sutherland who paid annual visits to the Roggeveld to serve the remote congregation, its population is little more than 3 600. Known locally as ‘land of snow and stars’, it is one of the coldest inhabited places in South Africa. With the cold come clear skies and multitudes of stars.
Things to do ■ Visit the Dutch Reformed Church (now a national monument); the Jewish Cemetery and the old English graveyard where soldiers of the South African wars of a century ago are buried; the Tuin-plaas church, with its dung floors and pedal organ, reputedly the oldest church in the country still used by farmers. ■ Take a pre-booked day or night tour of the SAAO – with its ten telescopes, including SALT, it is one of the world’s best astronomical sites. ■ Appreciate the vast, apparently stark and empty Karoo landscape – with its small free-roaming herds of springbok and dassies; its more elusive endangered riverine rabbits, caracals, and black eagle; and its unique flora. ■ Hike up the 66-million-year-old (inactive) volcano of Saltpeterkop. ■ Drive through the Gannanga and Verlatenkloof passes (and others) for their geological strata, excellent views, intricate stonework, and bountiful birdlife. ■ Enjoy the unusual, grass-free 9-hole golf course, 4 4 trails, and winter snowfalls. – Lisl Robertson ■ Information and bookings: tel. Karoo Hoogland Tourism at (023) 571 1265 or 082 556 9589; SAAO (021) 460 9319. For details about the SAAO Visitor Centre and monthly open nights call the SAAO at (021) 447 0025, or e-mail firstname.lastname@example.org, or visit www.saao.ac.za. You’ll find more on the Succulent Karoo Ecosystem Programme at www.skep.org.
Top: The stars appear to move around the South Pole because of the Earth’s rotation in this time exposure of the Sutherland night sky. Below: (left) The Iziko Planetarium; (middle) Karoo landscape; (right) Safety First. Pictures courtesy of the SAAO/SALT Foundation (unless otherwise specified)
Picture courtesy of Iziko Planetarium
Leaning back in a comfortable chair ‘inside’ the SALT dome, you look up at its towering structure, at the amazing 91-segment mirror ahead, with equipment around the periphery and, behind you, a ladder rising vertically to the catwalk high above. Sounds of humming machinery punctuate your cosmic odyssey. The scene projected on the hemispherical screen above you fills your vision as you turn your head. SALT is permanently tilted at a fixed angle (37 degrees) from the vertical, observing only those celestial targets that fall within its field of view. While this may seem a small area, almost the entire visible sky passes through that field as the Earth turns. Critical areas such as the Southern Cross region and the two Magellanic Clouds pass more slowly and spend much longer there. The planetarium can speed up the turning of the Earth to show how this happens. Planetariums present the night sky as you’d see it from the observatory. There’s no artificial light on that cold mountaintop as there is around cities so, with darkadapted eyes, you can make out thousands of stars. In this breathtaking sky, star clusters, glowing nebulae, and dark clouds dominate, as they should. South Africa’s planetariums invite you to an armchair trip that will transport you
into SALT – and billions of light years into space – to experience the new frontier opened up by one of our planet’s largest optical telescopes. – Anthony Fairall (Department of Astronomy, University of Cape Town/Iziko Planetarium)
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Letters to Living beyond our means really enjoyed the article on Earth’s Natural Capital (QUEST, vol. 2, no. 1, “Viewpoint”) in which it was indicated that, for everyone to live like an average American, we would need the resources of approximately six Earths. Your readers may be interested in the following facts related to this statistic. The figure of six Earths is derived from the Ecological Footprint for the United States which, according to the latest available data, is 9.5 global hectares per person compared to the productive area of the biosphere (that is, the area providing us with goods and services) of only 1.8 global hectares per person. By comparison, the Ecological Footprint
for South Africa is 2.8 global hectares per person, which is more than the world average of 2.2 global hectares per person and more than double the average for Africa of 1.2 global hectares per person. In other words, for everyone to live like an average South African, we would require approximately one and a half Earths. Of course, the average footprint value for South Africa masks regional differences within the country as well as differences between rich and poor, but the message is clear – we are spending nature’s capital much faster than it is generated. Rudi Pretorius, Department of Environmental Affairs and Tourism
B reaking down the barr i e r s o many articles in QUEST show one kind of science connecting with another kind in (for me) very unexpected ways. For example, for understanding how a gene works and changes the behaviour of a whole organism I need to know that the gene exists and also its structure and composition on an atomic scale (QUEST, vol. 2, no. 1, “Treasure from the molecules of life”). To create these exciting new hard materials for using in our hightech world, I need to know what a chemist knows, and also have the knowledge of a physicist, an engineer, and an expert in materials (QUEST, vol. 2, no. 1, “Getting to grips with strong materials”). But when I was at school, we learnt about science in different subjects called physical science or biology. They didn’t mix much. Is that still how things are at schools today? Perhaps this is why members of the public like myself have difficulties with modern science. People don’t really tell us how different parts of it connect – even though QUEST shows me that’s essential for science today. Scientists often seem to be far away from us, and find it hard to explain how the pieces in the jigsaw of science fit together. And the journalists also don’t say very much
about the connections. QUEST has told me about advances in science that I didn’t know about but, if they are so important, why don’t I read about them in our newspapers? J. Hendricks, Pretoria Connecting with science is not always easy, yet it is increasingly important as scientists find out more, as science becomes more complex, and as we depend more and more on its findings. Walt Whitman wrote a poem about such difficulties back in 1865: When I heard the learn’d astronomer, When the proofs, the figures, were ranged in columns before me, When I was shown the charts and diagrams, to add, divide, and measure them, When I sitting heard the astronomer where he lectured with much applause in the lecture-room, How soon unaccountable I became tired and sick, Till rising and gliding out I wander’d off by myself, In the mystical moist night-air, and from time to time, Look’d up in perfect silence at the stars. We are especially grateful to the scientists who write for Quest in ways that help us to overcome the barriers that Whitman experienced, and to appreciate the knowledge that is being generated all around us. – Editor
The best letter from a reader published in the next issue will win a Shaeffer pen. Address your letters to The Editor and fax them to (011) 673 3683 or e-mail them to email@example.com (Please keep letters as short as possible. We reserve the right to edit for length and clarity.)
Q Books Discover astronomy
Africa’s Giant Eye: Building the Southern African Large Telescope. By David Buckley, Marguerite Lombard, Mike Lomberg, Kobus Meiring, and Roelien Theron (Observatory: SALT Foundation, 2005). ISBN 0 620 34783 X This lavish book marks the inauguration of the Southern African Large Telescope (SALT) – the largest single optical telescope in the southern hemisphere and one of the first great scientific, engineering, and technological achievements of our new South Africa. This beautiful publication is dedicated to the memory of the late Bob Stobie who, as Director of the South African Astronomical Observatory, devoted the last years of his life to making this extraordinary project happen. Its pages tell the full SALT story from start to finish, paying tribute to the team that made it possible. It features highlights of South African astronomical history and situates the telescope in its remote Karoo location. It’s an illustrated journey through the stages of construction of this world-class facility, with its massive segmented primary mirror and state-of-the-art instrumentation. And it gives a vision of the opportunities that SALT offers to present and future astronomers to probe the mysteries of the Universe.
Starwatching – A Southern Hemisphere Guide to the Galaxy. By Anthony Fairall, illustrated by Margie Walter and Hershel Mair (Struik, 2002). ISBN 1 86872 738 6 Written for the general public, this book is packed with astronomical marvels. It introduces the celestial sphere and explains colossal scales of time and space by way of familiar analogies. Positioning us on the Orion Arm of the Milky Way, Fairall writes, “if our
Q Diary of events
Planetarium shows Galaxy were the size of Johannesburg, the Solar System would be about a millimetre across and it would lie somewhere in the vicinity of Sandton”, which leaves readers much more aware of their cosmic home address. In an excellent sequence of images entitled “The Universe on ever larger scales”, the book puts humans in perspective. Starting with an image of the Earth, and the tip of Africa marked ‘You are here’, it presents the Earth in relation to the Moon – again marked ‘You are here’. Once we reach the Solar System, the Earth is just a dot, and, relative to the gas giants Jupiter and Saturn we’re astonishingly tiny. The diagram showing the proximity of our nearest star made me realize how alone we are in the vastness of space. Venturing briefly into heritage and tradition, the author explores some of the astronomical complexities of the Egyptian pyramids and San and Xhosa mythology as well as some 19thcentury events at the Cape observatory, and Sir John Herschel’s completion of his telescopic survey of the entire sky – he’s probably still the only person to have done this. The book also discusses the Moon and Apollo landings, the bodies in our Solar System, and the nature of stars, extrasolar planets, galaxies, and other large-scale structures. And the star maps for the southern hemisphere give newly-inspired readers the tools to go and see for themselves. – Lisl Robertson
Read on ... Jansen, Albert, Star Maps for Southern Africa (Struik, 2004) ISBN 1 77007 005 2 Mack, Peter, Pocket Guide – Night Skies of Southern Africa (Struik, 1998) ISBN 1 86872 001 2 Penston, Margaret, Astronomy (New Holland, 2004) ISBN 1 84330 451 1 Slotegraaf, Alke (ed.), Sky Guide South Africa (Cape Town: Astronomical Society of South Africa, 2005). Available from the SAAO (Cape Town and Sutherland). Turk, Cliff, Field Guide Nagtehemel Van SA (Struik, 2001) ISBN1 86872 598 7 Turk, Cliff, Sasol First Field Guide to Skywatching of southern Africa (Struik, 2001) ISBN 1 86872 597 9
For more on southern African astronomy visit the South African Astronomical Observatory web site at www.saao.ac.za. For astronomy and space-related matters go to www.space.gov.za. You’ll find monthly South African star maps at the Cape Town Planetarium web site at www.museums.org.za/planetarium/resources.html and the Astronomy Picture of the Day Archive at antwrp.gsc.naza.gov/apod/archivepix.html. There’s more on the ESO 100-m optical telescope concept at www.eso.org/projects/owl/index.html. Worth visiting are NASA at http://science.nasa.gov/Astronomy.htm and the Hubble Space Telescope site at http://hubblesite.org. There’s an excellent educational site at http://starchild.gsfc.nasa.gov/docs/StarChild/Starchild.html.
Johannesburg Planetarium & Iziko Planetarium (Cape Town) Visit the new planetarium show on “The Southern African Large Telescope” (see p. 42), which tells the story of SALT, shows how the telescope works and what it sees, and updates visitors on SALT’s most recent observations. Daily shows 4 November 2005–end February 2006. For details, phone the Johannesburg Planetarium at (011) 717 1392 and the Iziko Planetarium in Cape Town at (012) 481 3900. Check what other shows are on for adults and children from now till the end of January 2006. (Note: the Iziko Planetarium closes for maintenance during late November.)
Power of Vision Outreach Great Hall, University of the Witwatersrand, Braamfontein “Power of Vision” presentations are offered to schools in Gauteng and farther afield as part of the National Astronomy Outreach programme. Students are welcomed by the Vice-Principal, Professor Thandwa Mthembu, then treated to Professor David Block in action as he offers the wonders of astronomy (including the differences between stars and planets, the places of stellar birth, cosmic dust, galaxies and clusters of galaxies, and concepts such as critical state analysis and chaos theory). These motivational talks intend to reach everyone, with or without a science or mathematics background, and to encourage learners to strive for their dreams and for excellence, both personal and academic. Sponsored by the TISO Foundation, Kagiso Exhibitions, and Pick’nPay, the talks last one and a half hours, followed by questions and a light lunch. For 2006 dates and details, phone Laurence Corner at (011) 717 1016 or 083 630 2362, or fax (011) 717 1065, or e-mail firstname.lastname@example.org.
Interested in astronomy? ■ The Astronomical Society of Southern Africa (ASSA), with centres around the country, offers membership to everyone interested in astronomy. ■ The Cradle-Ribeiro Observatory, in the Cradle of Humankind Heritage Site near Pretoria, presents general astronomy shows and talks to the youth, the public, and tourists. For details phone 082 682 4062. ■ The Rhino and Lion Nature Reserve Observatory at the Wonder Cave, outside Krugersdorp, near Sterkfontein, holds regular star parties, talks, and shows. ■ Port Elizabeth People’s Observatory is open to the public on the 1st and 3rd Wednesday each month and every Wednesday in December and January. Admission is free of charge. Group viewing evenings may be arranged at other times. ■ Cederberg Observatory holds public open nights every Saturday except or near full moon (weather permitting). For details phone (021) 913 4200. ■ Astronomy Africa provides astronomical products and services (from design and construction of private observatories to education and training courses) aimed at advancing astronomy in Africa. For more phone (011) 205 9040. ■ Boyden Observatory, outside Bloemfontein, has telescopes for research and educational purposes. For more phone (051) 401 2924.
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Q Q UEST crossword
Q ASSAf News
You’ll find most of the answers in our pages, so it helps to read the magazine before doing the puzzle. 3
Science-for-Society Gold Medals 2005 10 11
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22 23 24
11 13 14
Celestial body, other than a satellite or comet, that revolves around the Sun in the Solar System (6) A story, either invented or true, handed down from the past (6) The late Dr Bob ---, a driving force behind the Southern African Large Telescope project (6) A light particle (6) A particle of dust (4) Descriptive of rays with a wavelength just outside the visible range (8) A branch of science which should be studied at school by would-be astronomers (7) A massive assembly of star systems; each having millions of stars, nebulae and dust (6) An astronomer who studies the origin and evolution of the universe (11) His Law of Computing maintains there is a doubling in CPU complexity and memory capacity every two years (5) A component part of the new telescope at Sutherland, which follows a target object across the sky (7) World-class Namibian telescope (4) A spinning neutron star that emits energy along its axis of rotation (6)
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5 7 8 9
22 23 24 25
The gaseous state of hot ionized material consisting of ions and electrons and present in the stars (6) A home for pyramids (5) Type of minor planet composed of rock and metal, which moves around the Sun (8) A hot glowing fragment of coal or wood left in a dying fire (5) A collection of facts or information (4) The point of the heavens directly above the observer (6) The longest-lived and most common star; low-mass, cool, and faint (3,5) A pioneering telescope in Texas (3) An object with a gravitational field so intense that no matter or radiation can escape from it; believed to result from the collapse of a star (5,4) The largest single optical telescope in the southern hemisphere, and equal to the largest in the world (4) Rays of very short wavelength emitted by radioactive substances (5) Covering of an optical telescope (4) Small celestial body that orbits the Sun; having an icy nucleus and a tail of evaporated gas and dust particles (5) A celestial body; a luminous point in the night sky (4) A superior location for astronomy (5) A US agency responsible for aeronautics and space flight (4) Outer space as viewed from the Earth (3)
On 28 October 2005, the two annual ASSAf Science-for-Society gold medals were awarded to Professor Thomas Bothwell and Professor George Ellis for outstanding achievement in the application of scientific thinking in the service of society. Thomas Bothwell, Emeritus Professor of Medicine at the University of the Witwatersrand, has spent a lifetime investigating world health issues associated with iron in the human body. What food factors inhibit iron absorption in many cereal-based diets in developing countries, Bothwell asked? The answer was polyphenols (found in tea, sorghum, and legumes). His Chatsworth trial using curry powder fortified with iron-EDTA complex was a landmark demonstration that iron fortification works. The approach is now applied in the Far East and Bothwell’s contibutions continue in national fortification programmes around the world. George Ellis, Emeritus Professor and Distinguished Professor of Complex Systems at the University of Cape Town, is a world leader in the areas of general relativity and cosmology, but has also published on neural development and the brain, science policy, social development, science and mathematics education, and the relationship between science and religion. He has received the Star of South Africa and, in 2004, the Templeton Prize for his investigations into the relationship between science and spirituality. He advocates a balance between the rationality of evidence-based science and the consideration of phenomena beyond science’s ability to explain (in ‘causally effective’ areas such as aesthetics, ethics, metaphysics, meaning, morality, faith, and hope). His involvement with problems ranging from public administration to the plight of homeless people has brought him recognition from scientific elites and the poorest of the poor.
SAJS centenary awards The hundred-year-old multidisciplinary scientific research journal, the South African Journal of Science (SAJS), now published by the Academy of Science of South Africa, is the pre-eminent international platform for demonstrating and ‘branding’ the body of science and quality of research conducted in South Africa. By gathering together all the strands of the country’s scientific research, it shows readers – locally and abroad – what science is happening here. The most recent available impact statistics rank it 14th out of the 46 international journals of its kind. ASSAf’s four special centenary awards recognize this milestone in the life of South Africa’s leading research journal. ■ To Professor Johann Lutjeharms, two awards – in recognition of his having contributed the greatest number of original articles, and having been associated with the greatest number of SAJS covers, during the last quarter-century. Johann Lutjeharms has put his area of South African research on the world map. His many papers – and covers – in the SAJS have demonstrated the importance of our region and of South African scholarship to a proper appreciation of the global atmospheric and oceanographic sciences. ■ To Professor Phillip Tobias, the special Editor’s Award in recognition of his sustained and unstinting contribution of advice, original articles, and personal encouragement to the editor during the last quarter-century. Since Graham Baker arrived in South Africa, in 1972, with the task of developing the SAJS along the lines of Nature, Tobias has been an everpresent and valued part of the journal’s scientific landscape, as author, adviser, and mentor to generations of young researchers who themselves became valued and regular contributors to the Journal. The SAJS has benefited from the steady stream of papers that came to it through the efforts of its two Centenary award-winners. Lutjeharms and his colleagues have contributed original research in (and above) the Agulhas Current, in the Benguela Current, and in the scientifically rich waters of the Southern Ocean as far as Antarctica. Through Tobias have come contributions based on excavations in the Cradle of Humankind. A high point was the announcement of the discovery at Sterkfontein of the skeleton of Little Foot by his colleague, Dr Ron Clarke, in late 1998. ■ To Dr Graham Baker, special ASSAf Award in recognition of his unstinting commitment and high professionalism in the development over more than three decades of the South African Journal of Science as the premier organ in Africa for the publication of internationally significant, multidisciplinary research. Having obtained his Oxford doctorate in solid state physics, Baker started his career in science publishing working on Nature and other Macmillan Journals titles in London. He took over the editorship of the virtually defunct South African Journal of Science in 1972. Since then, he has developed it into South Africa’s key scientific research journal. As he often says, this growth and this achievement of excellence cannot happen without the ‘invisible college’ of scholars and supporters who actively help to make the Journal what it is.
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Back page science Q Le stink Apparently there’s a real need to describe exactly how various cheeses taste and smell. Researchers at Kansas State University have been working on 43 French varieties. “The 31 attributes ... can be classified into seven categories: fundamental tastes, dairy aromatics, fatty acid/animal, musty/fungal, aged/fermented, mouthfeelings, and other aromatics,” they say. Yum yum – fungal with mouthfeelings! (From www.sciencedirect.com.)
Out on the edge The MIT’s Technology Review publishes lists of “10 emerging technologies that will change your world”. The May 2005 list is: airborne networks; quantum wires; silicon photonics; metabolomics; magnetic-resonance force microscopy; universal memory; bacterial factories; enviromatics; cellphone viruses; and biomechatronics. What are these things? Well, enviromatics, for example, is a new field in which IT meets environmental studies on intimate terms, making sense of huge amounts of data as the basis for decisions about things like agriculture.
Think of it like this ■ “A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of ideas.” John Ciardi (1916–1986), American poet. ■ “Science is organized knowledge. Wisdom is organized life.” Immanuel Kant (1724–1804), German idealist philosopher. ■ “I am among those who think that science has great beauty. A scientist in the laboratory is not only a technician but also a child placed before natural phenomena which impress him like a fairy tale.” Marie Curie (1867–1934), physicist and chemist and winner of two Nobel prizes. ■ “Technology is a way of organizing the universe so that people don’t have to experience it.” Max Frisch (1911–1991), Swiss writer.
■ “Never let the future disturb you. You will meet it, if you have to, with the same weapons of reason which today arm you against the present.” Marcus Aurelius Antoninus (AD 121–180), Roman emperor.
Don’t do it! The journal Science reported evidence that the brain’s anterior cingulate cortex – also known as the ‘oops centre’ – tries to prevent its owner from making mistakes. Researchers figured this out by tricking subjects who were playing a computer game. But the oops centre clearly wasn’t working for the students who gave these answers in science exams, according to an e-mail doing the rounds: Q: How are the main parts of the body categorized? (e.g. abdomen) A: The body consists of three parts – the brainium, the borax, and the abdominal cavity. The brainium contains the brain; the borax contains the heart and lungs, and the abdominal cavity contains the five bowels, A, E, I, O, and U. Q: What is the fibula? A: A small lie. Far more timid is the approach to science in British classrooms and school laboratories. An article on the web site Spiked-Online says many teachers either think they are not allowed to take any risks (fun things like explosive chemical reactions) or can’t be bothered to reduce the risks. Yet, according to a science education authority, science lessons account for only a tiny fraction of accidents in schools – statistically, the sports fields are the real danger zone.
Face it, kid ■ Nicholas Bakalar writes in The New York Times (May 3 2005) that “Canadian researchers have made a startling assertion: parents take better care of pretty children than they do ugly ones. Researchers at the University of Alberta carefully observed how parents treated their children
during trips to the supermarket. They found that physical attractiveness made a big difference....” That can’t happen outside Canada, can it? ■ The BBC says some UK schools are encouraging children to drink more water to improve their concentration. So water isn’t always a diluter!
You can’t stop the music Ever had an annoying tune ‘on your brain’? For more about these ‘earworms’ and the science of music visit www.exploratorium.edu/music. On 94.7 Highveld Stereo there was recently a competition to identify everyday noises that were broadcast in short bursts of sound. Not easy – find out why by going into the exploratorium’s ‘kitchen’.
Real frontier science During World War 2, English scientists who were working on the antibacterial properties of penicillin injected it into their clothes for safekeeping, in case they had to restart their research after a German invasion. For more about this vital work, read Eric Lax’s The Mould in Dr Florey’s Coat: The Remarkable True Story of Penicillin (Little, Brown 2004). Another man with a plan in that war was Charles Fraser-Smith, who supplied secret agents and prisoners of war with gadgets, often ordinarylooking items, containing secret compartments. He was the character on whom Q was based in Ian Fleming’s James Bond stories. For more, follow the POW link on www.sneakyuses.com. Answers to Crossword (page 47) ACROSS: 3 Planet, 6 Legend, 10 Stobie, 11 Photon, 13 Mote, 14 Infrared, 16 Physics, 18 Galaxy, 21 Cosmologist, 26 Moore, 27 Tracker, 28 HESS, 29 Pulsar. DOWN: 1 Plasma, 2 Egypt, 4 Asteroid, 5 Ember, 7 Data, 8 Zenith, 9 Red Dwarf, 12 HET, 15 Black hole, 17 SALT, 18 Gamma, 19 Dome, 20 Comet, 22 Star, 23 Karoo, 24 NASA, 25 Sky.
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