"EverySpace Magazine International - #1"

“EverySpace Magazine International” - #1 September 30, 2012 Free online distribution ISBN: 9788897004240

Magazine

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EverySpace S.r.l.

International

September 2012 - Free Online Distribution

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“EverySpace Magazine International” - Issue 1 International edition of “EverySpace Magazine” - #1 Online publication date : September 30, 2012 Online Publication Responsible: Issuu Creator of “EverySpace Magazine” ‘s project: Simone La Torre Editor in Chief and Senior Director: Michele Caruso Company responsible of this project: EverySpace S.r.l.

President: Simone La Torre General Manager: Mattia Stipa Website: www.everyspacedivision.com ***** Supplement to information and culture newspaper “Vento Nuovo” Rome’s Court Registration n. 43 on 24.02.2010 Published on occasional cadence. ***** All of “EverySpace Magazine” and “EverySpace Magazine International” authors and contributors give their own contribution freely, accepting every responsibility in any case of copyright dispute and intellectual property used in their articles.

“EverySpace Magazine” Editorial unit gives its disposal to the party entitled, in those cases where it wasn’t possible to date back the holders of intellectual properties of topics, citations or images used in this number. ***** Advertising on this page is subject to fee. ***** Editorial supervision, graphics, layout, and quality technical assurance by EverySpace S.r.l “EverySpace Magazine” is an exclusive project of EverySpace S.r.l.

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ESMI- #1 Agenda

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Welcome!

by S. La Torre

How was “EverySpace Magazine International” born?

The never-ending journey through sidereal space.

by M. Caruso

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What is Space made of?

by A. Pizzoferrato

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The Constellations and the Zodiac

by P. Carugno

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The 8 Planets of the Solar System.

by A. S. Mezzapesa

How do Rockets fly?

by U. Pica

How does the Satellite Navigation System work?

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by M. Sciarra

Contact us!

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Welco me!

Dearest readers, welcome to the pages of “EverySpace Magazine International” 's first number!

Let me tell you a secret: advanced science and technologies may result unexpectedly thrilling, if presented to the public through passionate academics’ words, without the sterile (and sometimes pernicious) linguistic-interpretational mediation, typical of the journalistic field.

“EverySpace Magazine International” is the English edition of the Italian project “EverySpace Magazine” and represents an ambitious editorial project, whose goal is to involve you and explain to you, thrill, surprise, and sharpen you, showing the most complex concepts in the only way any of us would love to learn about them: as if we were being told by our best friend!

But which authors are able to write simply about the impossible? Where are the real fans, the only ones able to spread ideas with extreme clarity and enthusiasm?

Questions easily answered: at university!

Our authors are university students inspired by their study courses. Thanks to them, “EverySpace Magazine International” has what it takes to fascinate you readers dealing with what is difficult in a simple way… Because in real life, when you know the solutions, problems do not exist!

Wishing you a good reading would be, at this point, definitely inappropriate and insufficient; hence, it is with my great pleasure that I wish you a “cosmic reading”!

Simone La Torre

President and Co-Founder of EverySpace S.r.l.

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How was ”EverySpace Magazine International” born?

“EverySpace Magazine International” is the English edition of “EverySpace Magazine”, a popular Italian scientific magazine, conceived by students for students!

Our authors are not journalists indeed, but students at university faculties such as Space Engineering, Aeronautical Engineering, Physics, Telecommunication Engineering, and Mathematics .

“EverySpace Magazine” ‘s goal is to draw pupils of junior high and high school (and curious people of any age) closer to scientific issues, answering to typical questions that any of us, aware or not, has wondered about.

The team of “EverySpace Magazine” wishes to spread technical/scientific concepts, typical of the aerospace field, publishing simple-to-read articles, written in a conversational and straight color.

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Italy as seen from space - Source: ESA’s portal.

“EverySpace Magazine”,

The Space, Simply!

Like us on facebook: www.facebook.com/EverySpaceMagazine

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International Space Station (ISS).

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Artistic representation based upon photos taken by Hubble Space Telescope. Source: NASA’s portal.

The never-ending journey through sidereal space.

by Michele Caruso “EverySpace Magazine” 's Editor in Chief and Senior Director

I have always been fascinated by the idea that men, a Created’s pavid bit, an itsy-bitsy particle within an infinite universe, is able to see such a clear vision, to measure such an accurate measurement, what eyes cannot see and hands cannot reach.

Thanks to its curiosity, to its thirst for knowledge, to its constant attempt to overcome its own limits, human mind is able to peer at the unknown, to appreciate the incommensurable, to fix into an extemporary portrait, into an unknown notes sequence, the sidereal space’s vastness.

“EverySpace Magazine” aims to be a journey to such cosmos’ abyss. It is great to give birth to such an adventure, which carries on the infinite, through William Blake’s superb words : “To see a World in a Grain of Sand, and a Heaven in a Wild Flower, hold Infinity in the palm of your hand and Eternity in an hour”.

Have a great trip to all of us, hoping to come back with new eyes!

What is Space made of?

by Andrea Pizzoferrato Student of Physics Translation by Luca Nardini

“Space, the final frontier.

These are the voyages of the starship Enterprise.

Her mission: to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before.”

[Star Trek - The future begins, 2009]

Virtual image created with Stellarium®.

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You all certainly have looked up to the sky. You all have looked at it both during night and day.

Therefore, you have seen the Sun, the clouds, the colors of sunset, the stars, maybe some comets and the Moon.

However, paraphrasing Richard Feynman's words, compared to a scientist looking at the sky, would you see more or less than him? Your imagination, that completes what your eyes perceive... what is its limit? Apart from mere glows in the night, what do you see? During the day, what do stars look like?

Well, let's take one step at the time. The universe is so big, whereas we are so small; is it rightful for us to study it? Easy question, difficult answer. The astrophysicist Carl Sagan used to say: “We are starstuff contemplating stars.” In the end, studying the universe also entails a journey inside our inner selves and our primordial nature, a study of the minuscule linked with immensity. Like every study that aims to grasp the basics behind something, before analyzing the clockworks of the huge clock that we call universe, we must look at this system as a whole and ask ourselves: what is space made of? Space is made of everything and nothing at the same time.

Let's see why.

Looking at a clear blue sky during the day, this is more or less what we would see:

ESMI- #1 Let's now reduce the intensity of the dazzling sunlight and take away the atmosphere that obscures the stars' light. Good, everything is ready. This is the sky that we would see during the day:

Virtual image created with Stellarium速.

We can notice the presence of the Sun, so big because is closer to us and then some other colored stars. What, colored?! Are there red and azure stars? Why are we stuck with a Sun (that is a star itself) that is apparently yellow? Generally speaking, the stars' color depends on the chemical reactions that involve the elements that constitute the stars. These reactions also depend on the stars' age. Stars do not stay forever in one form. They are born and grow like us living beings. For example, the Sun is 5 billion years old and is half way through its estimated lifetime. But let's focus on the sky once again: where have the planets gone? Are they not there during the day? Actually, planets look like small shining dots, just like stars. Let's try to highlight them and here they are (together with other celestial bodies):

Virtual image created with Stellarium速.

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However, if the universe is so big and full of stars, why do not all their lights reach us? I mean, with all those stars up in the sky, the night should be bright almost like the day! This is the Olbes paradox; up to now no solution has been found to solve it. Some claim that, due to the expanding universe, the light of some stars will never reach us because they are now too far away; but is the universe really expanding? If so, from where did this expansion start? Also to answer this question, scientists came up with a lot of fascinating theories, but none of them is a definite one. Since many years the most accepted one is the Big Bang theory, which states that the universe was born from a fast expansion from a minuscule spot where it was concentrated. From this bizarre phenomenon, a lot of complex cosmical structures of unmatched beauty were born, like the Pillars of Creation in the Eagle Nebula, or the Pleiades.

The Pillars of Creation in the Eagle Nebula.

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Moving on, apart from stars and planets, what else is there? Is all that dark made of nothing?

Absolutely not, and it is even more mysterious of what is visible. In fact, we know that the planets' orbit is regulated by the universal gravitational law, which states that two objects with a mass attract each other. This attraction is stronger when they are very near to each other or when their “weight” is heavy. The same goes for the Solar System and all the celestial bodies inside it: the eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune), asteroids, comets, the Sun, etc.

Sir Isaac Newton was the first to formulate this law that was accepted by the scientific community 300 years ago and it is still valid. However during the 20th century, scientists found evidence that in some areas of the universe, particularly in spiral galaxies, the orbit of some stars does not coincide with the one calculated with the application of the universal gravitational law. Usually, a celestial body's orbit is determined by the attraction of all the other bodies around it. If the orbit does not follow the so calculated path, this would mean that there are objects with “weight that we can not see”. This “invisible weight” is what is called “dark matter”, a material that unlike ordinary materials, does not emit light after chemical and physical reactions. However dark matter is not the only element that causes great variations from the trajectory given by Newton's law. As you may have already heard, there is the hypothesis of the existence of black holes, according to which there are objects (which are stars that reached the end of their lifetime) so dense to attract even light (as explained by Albert' Einstein's theory of relativity) that is not made of matter.

Artistic representation of a Black Hole.

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To sum up, in our journey we have seen a group of some of the known objects (so far!) that are part of the cosmos, from the Big Bang to black holes, from big and shiny suns to mysterious and lonely black stars. So let me ask you Mr. Feynman's question once again: now, when you look to the sky, what can you see?

The Pleiades.

References for “What is Space made of?” - May 2012 in Italy http://anthalideus.files.wordpress.com/2010/12/pillars-of-creation.jpg http://upload.wikimedia.org/wikipedia/commons/d/d4/BlackHole.jpg http://it.wikipedia.org/wiki/File:Pleiadi_it.jpg

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Anyway, after being dragged inside a black hole, where would we end up? The hypothesis is that after reaching a distance called “Horizon of Events” is not possible to escape from the black hole, no matter what you try. So, once inside, what happens? Some believe that space-time tunnels would open, tunnels that connect two distant points of the universe to different periods of time. In any case, it is good to highlight the word “hypothesis”. In fact, for now nothing is certain and there are a lot of alternative models. For example, the theory of gravastars, which entails that a dying star does not become a black hole, but a bubble of nothing. Or the theory of black stars, objects similar to black holes, but without “Horizon of Events”. What is the purpose of black holes anyway? From their description they sound like giant energy parasites. Actually, some scientists think that at the center of our galaxy (just like Andromeda) there is a black hole that maintains the equilibrium of the galaxy itself during its rotating dance. We all are part of this eternal motion from one sector of our galaxy (the Milky Way) called Orion-Cygnus Arm, where the Solar System is, and therefore the Earth as well.

Mini-Glossary

The 8 Planets of the

AU: Astronomical Unit. It is a unit of length equal to the mean Earth-Sun distance (149,597,870,691 kilometers).

Solar System.

Magnitude of a star, a planet or another celestial body: it is the measure of its brightness as seen from Earth. The brighter the object appears, the lower the value of its magnitude.

by Antonio Simone Mezzapesa Student of Space Engineering Translation by Luca Nardini

In the end, it is almost all empty...

Do not let yourselves be fooled by art representations that you usually find on posters (or on this magazine), the Solar System is really enormous! Distances are so big that a scale representation is also impossible. Should Earth be as big as a marble, Jupiter would be placed 300 meters away from her, whereas Pluto (that would be as big as a bacteria, thus invisible to human eye) 2 kilometers and a half away! Pluto is not even the last “object� of the Solar System. In fact, the former planet, now considered a dwarf planet, is placed only at one thousandth of the distance to the border of our system!

Moreover, all visible objects (the Sun, the planets and dwarf planets, the moons, the asteroids, the comets, etc.) only account for one trillionth of the total space in the Solar System! Basically, few grains of matter amidst a lot of nothingness. How was all this born?

Artistic representation of the Solar System

All the planets go around the Sun (revolution), approximately on its equatorial plan, following a counter-clockwise path if we look down form the North Star. In addition, both the Sun and (almost) all the planets, rotate around their axis (rotation) counter-clockwise and so do their satellites around their planets, on an almost circular elliptic orbit.

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ESMI- #1 All this seems regular enough to make us think that the entire Solar System was born from a single process, but which one? A lot of theories have been proposed during many centuries, but nowadays the most accepted one is the theory that states that everything was born from a giant cloud, where a series of vortexes and sub-vortexes later condensed and originated the Sun, the planets and the satellites.

According to studies on asteroids fallen on Earth, all this supposedly occurred 4,5 billion years ago.

The 8 Planets - ID cards.

Planet

Rotation

Revolution (in terrestrial years)

Mean distance from the Sun (in AU)

Mercury

58,65 terrestrial days

0,241

0,378

Venus

243 terrestrial days

0,615

0,723

Earth

24 hours

1

1

Mars

24,62 hours

1,881

1,564

Jupiter

9,8 hours

11,86

5,209

Saturn

10,2 hours

29,46

9,539

Uranus

17 hours

84,32

19,18

Neptune

19,1 hours

164,8

30,06

Four little interesting rocks.

Mercury and Venus are the only two planets between Earth and the Sun. Venus is the easiest to observe. Firstly because is bigger than Mercury, secondly because, when at full brightness, its magnitude is -4.22 which makes it the most luminous celestial body after the Sun and the Moon. On the other hand, been Mercury so close to the Sun it is possible to see it only when it is near the horizon, or during dawn and sunset.

Mercury has no atmosphere and is full of craters. Due to its proximity to the Sun, it was believed that its rotation period would be the same as its revolution period, just like the kind of gravitational coupling between the Earth and the Moon would entail. However, it was discovered that the rotation period is exactly 2/3 of the revolution period. It still is a strong gravitational coupling, but not strong enough to synchronize the two periods (on the contrary, the Moon's rotation and revolution period are more or less the same).

Unlike its neighbor, Venus is covered by dense clouds (Venus' atmosphere is 90 times denser than Earth’s one) made of carbon dioxide and a small percentage of nitrogen. The space probe Mariner 2, the first one to successfully reach Venus, detected a surface temperature equal to 425°C (797°F)! Underneath Venus' atmosphere (as another space probe, the Pioneer Venus, found out) there is only one enormous continent, that accounts for about 5/6 of the planet surface, almost completely flat. Moreover, Venus has no gravitational coupling with the Sun and its rotation is clockwise, the opposite of the rest of the planets.

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Mars, the fourth planet from the Sun right after the Earth (that we are not going to describe in this article since we presume that the majority of the readers live on it), is a relatively small planet, that is however pretty easy to observe (it is the brightest planet after Venus). Mars has two features similar to the Earth: it rotates on its axis in a little more than 24 hours and a half (the Earth takes 24 hours) and its axis has a 25° degrees inclination (a bit more than the 23.45° degrees of the Earth). This means that Mars has seasons similar to the Earth, although they last twice the time and are much colder. Mars' density is much less than the first three planets, so it is believed its inner iron core is very little. At the beginning of the 70s, the space probe Mariner 9 made a very detailed map of the red planet, thus proving that the famous Mars canyons... do not exist!

In fact, it is just an optical illusion, although there is a big canyon (Valles Marineris) that may have tricked some astronomer in ancient times. The rest of the surface is dotted with craters (especially in the Southern hemisphere), but also with some mountains that are probably still active Picture of Mount Olympus - Mars. volcanos (the highest one, Mount Olympus, is 27 km high).

Big and huge, but good.

Jupiter is the giant of our Solar System. Its diameter is approximately 11 times than Earth’s one, while its mass (more than 300 times Earth’s mass) is more than twice of all the other planets put together.

On the other hand, its density is much less than the one of the Earth, since it is mainly composed of gas substances. For this reason it has been nicknamed “the gas giant”. Due to its -2,5 magnitude Jupiter is brighter than any star. It is almost always the brightest dot in the night sky and this is why it carries the name of the father of the gods of the Greek and Roman mythology. Jupiter was one of the first objects observed by Galileo Galilei with his telescope. He discovered 4 small stains on the planet and deduced that those objects were orbiting around the planet itself: he discovered the four satellites later called Galileans or Medicean moons (Io, Europe, Ganymede, and Callisto). In 1892 a fifth satellites was discovered with naked eyes (Amalthea) while, later, more were discovered, called external satellites, thanks to photographs taken by powerful telescopes or space probes. Up to now, something like 63 satellites have been identified!

Jupiter (left) and Venus (right) in the night sky.

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Jupiter also has a feeble system of planetary rings, but much less spectacular than the one on Saturn. This is the second biggest planet in the Solar System, immediately after Jupiter. Its mass is 3/10 of the giant, while its equatorial diameter is 5/6 of Jupiter’s one. However, since its volume is only 6/10 of Jupiter's, Saturn is the least dense object in the Solar System. In 1656 Christiaan Huygens understood that there was an external ring around the planet that did not touch Saturn in any point, whereas in 1675, Giovanni Domenico Cassini noticed a dark line (Cassini division) and assumed that there might be two rings, an internal and an external one. From then onwards scientists talked about the planetary rings using the plural. Actually, now we know that the rings are a series of concentric disks of material caught by Saturn's gravity. Apart from the rings, Saturn has a bunch of satellites, just like Jupiter. Among them, the most peculiar one is Titan, the only satellite in the Solar System whose atmosphere is almost completely made of methane.

The third gas giant, Uranus, is a lot smaller than Jupiter and Saturn. Its mass is 5/33 of Saturn, although it has 14 times the Earth's mass.

Uranus is a lot less bright than the other two gas giants, however, if we look in the right direction, it is still visible to the naked eye in a very dark night. What is curious about this planet is that its rotation axis has a 98° degrees inclination. During its revolution, the planet seems to roll on its side!

Shortly after the discovery of Uranus, scientists calculated its orbit and strong anomalies were noticed. In 1845, Mr. Adams, an Oxford University student, calculated the orbit and the position of an hypothetical planet beyond this gas giant, whose gravitational attraction would have explained Uranus' anomalous trajectory. In 1846, the planet was actually found around the calculated position and was named Neptune. This planet has a slightly smaller diameter than Uranus and it has 17 times the mass of the Earth. It is the fourth gas giant of the Solar System. Neptune has satellites as well, among which there is a fairly big one (Triton) that, for some unknown reasons, rotates in the opposite direction despite its dimensions and the proximity to Neptune.

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Picture of Saturn’s ring.

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The 5 dwarf planets.

Apart from Neptune, there is a series of celestial bodies called trans-Neptunian objects, whose orbits are mostly beyond the one of the planet dedicated to the god of the sea. Pluto is the most famous of this objects, since at first it was classified as the ninth planet of the Solar System. For almost 50 years after its discovery (that occurred in 1930), Pluto was believed to be bigger than Mercury but, after, the discovery of its moon (Charon) allowed scientists to make an accurate estimate of Pluto's mass, which accounted to just 1/20 of Mercury's mass, thus making Pluto by far the smallest planet. In the 90s astronomers started to discover other objects in the same region where Pluto's orbit lies (known as Kuiper belt) and others at an even greater distance. Some of them shared the key features of Pluto's orbit, so this celestial body started to be considered as the biggest of a new class of objects, the plutinos. This fact made some astronomers stop referring to Pluto as a planet, but as a “minor planet�, sub-planet or planetoid until 2006, when it was decided to label Pluto (and other objects discovered later) as a dwarf planet. Up to now, the objects classified as dwarf planets are: Ceres (within the asteroid belt between Mars and Jupiter), Pluto, Haumea, Makemake (in the Kuiper belt) and Eris (beyond the Kuiper belt, in a region called scattered disk).

The borders of the Solar System (aka: Mom, I won't be back home for dinner!).

We have so far introduced the 8 planets and the bodies that orbit around the Sun, but where does the Solar System end? There are two criteria to define this border. The first one takes into account the propagation of the solar wind (the external border created by the particles that compose the solar wind is about 4 times the Sun-Pluto distance. Then there is what is called heliopause, that is considered to the beginning of the interstellar medium). The second criterion takes into account the actual radius of the gravitational influence of the Sun (which apparently reaches out until 1,000 times more than the strongest solar wind).

To get an idea of how far this borders are, just think that at the end of 2007, the space probe Voyager 2 sent to Earth data that may indicate its crossing of the heliopause. The probe was sent (just like its twin, Voyager 1) to the borders of our system in 1977 and now are at approximately 15 billion kilometers from the Sun!

Position of the space probes Voyager 1 and Voyager 2 and a map of the borders of the heliosphere.

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References for “The 8 Planets of the Solar System” - May 2012 in Italy

Bill Bryson, Breve storia di (quasi) tutto, Capitolo 2: Benvenuti nel sistema solare, TEA, 2008.

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Isaac Asimov, Il libro di fisica, Parte III: Il sistema solare, Mondadori, 1986. http://it.wikipedia.org/wiki/Sistema_solare. http://it.wikipedia.org/wiki/Formazione_ed_evoluzione_del_sistema_solare. http://it.wikipedia.org/wiki/Giove_(astronomia). http://en.wikipedia.org/wiki/Orbital_period. http://theanswermachine.tripod.com/id2.html.

The Constellations and the Zodiac.

by Piera Carugno Student of Aeronautical Engineering Translation by Claudia Alvarenga

“He first, I following until I saw, through a round opening, some of those things of beauty Heaven bears.

It was from there that we emerged, to see once more the stars.”

(Dante Alighieri, Divine Comedy - Inferno, Canticle XXXIV)

Ever tried to recognize constellations? Ever wondered what’s the real difference between ”constellations” and ”star sign”? Ever tried to figure out what distinguishes astronomy from astrology?

If “yes” is the answer to all these questions, you just have to keep on reading and all your doubts will vanish.

Let’s start off noting that behind a simple observation of the sky (which some might consider a trivial fortune teller’s hobby) lies a ”universe” of studies and careful observations of the celestial sphere.

Though, to get the hand on such complexity, it must be understood what the objects of the study of astronomy (and, later on, astrology) are. In other words, it becomes necessary to ask yourself: ”what is the celestial sphere exactly? And what’s the real difference between constellations and star signs?”

Usually, by ”celestial sphere” is meant a sphere of a chosen radius, above which all the constellations (a group of stars, with well defined boundaries) are projected: the sphere’s center may be either the Earth (geocentric sphere) or the Sun (heliocentric sphere). In order to better picture this idea in our minds, let’s think of a mellon and imagine to be precisely at its center. What we see, if we look at the walls from the inside, is many seeds carved into the fruit’s peel (or into the pulp), which, from our viewpoint, are fixed.

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ESMI- #1 Such is the celestial sphere, just as observed from the Earth: a huge balloon of an infinite radius, on which we find stars carved into its internal surface. Now, let’s try to make things clear: what is meant by ”carved” stars? And why is the radius considered as infinite?

First of all, we have to quantify the Earth-stars distance in order to understand the magnitude of the numbers we’re dealing with! It’s been estimated that a space probe moving at 70 km/s would reach Proxima Centauri, the closest star to the Earth other than the Sun, after 18000 years (more or less!). This leads us to understand how the stars we observe are light years away from the Earth, that is we are dealing with distances unfamiliar to human beings, but very common for field’s experts such as astronomers, astrologers, astrophysicists and aerospace engineers.

In addition to interstellar distances, it must be considered that stars have their own rotary motion around the center of their galaxy, just like (scaled down) Earth and the other planets of the Solar System rotate around the Sun. Though, because of the huge distance between Earth and Stars, the stars’ rotary motion around the galactic center results undetectable to our eyes, which is why we don’t even notice it and consider the stars to be ”fixed”, in other words, carved into the celestial sphere.

The celestial sphere may be considered as a sphere of an infinite radius to be used as a painting board to project and define constellations.

Astral projection onto the celestial sphere.

Representation of the geocentrical celestial sphere.

By ”constellation” is meant one of the 88 sectors in which the celestial sphere is arbitrarily divided into; each sector is made of a well limited group of stars, so that every star belongs to and only to one constellation through the whole year. Over the past centuries, each group of stars has been referred to using name generally inspired by Greek mythology in order to remind precise shapes and pictures, even though hard to recognize, sometimes.

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Using the celestial sphere as a plane to project stars has only a practical (and symbolical) meaning because, as said before, distances between stars are significant (sometimes huge).

The subdivision in 88 sectors was made at the beginning of 900 by IAU and, among those 88, 48 were already known by Greeks and catalogued by Tolomeus.

Often, the idea of ”zodiacal constellation” is associated to the one of ”constellation”, the former being the object of study of astrology (the subject - as to define it ”science” results in a mere linguistical abuse - dealing with the star signs, based on the belief that the stars’ motion might have an influence on human behavior). In years, astrology has lost its scientific/technical value becoming nothing else but a divinatory practice; despite that, its characteristic elements, that is zodiacal constellations, are known to ”the public” and often confused with proper objects of astronomy: constellations.

In astrology, zodiacal constellations (also known as ”star signs”) belong to a celestial belt, called ”zodiac” whose extension foes for 18 °C perpendicular to the ecliptic’s equator (being the ecliptic the apparent path of the Sun in one year). Such belt is divided into 12 equal sections, each of 30 °C, which the Sun periodically runs throughout the year. Thus, if we once observe a certain zodiacal sign in the night sky, it means that the Sun is ”going across” the opposite constellation in the zodiacal belt at that time (simply put: if we raise our eyes at night and see the ”Cancer” constellation, it means that the projection of the Sun onto the celestial sphere is passing in the ”Capricorn” constellation) .

Representation of the Sun, while crossing contellations.

Actually, the Sun moves across 13 constellations and not only 12, like the ones belonging to the Zodiac! The 13th, or ”hidden” constellation is Ofiuco’s, the only one which did not name any star sign. Ofiuco is completely visible from almost everywhere on Earth (exception made by polar caps) and may be easily identified because its shape reminds of a man powering a snake.

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ESMI- #1 By what just said, then, it is easy to gather that not every constellation and star sign is visible throughout a whole year . This is because of several reasons : firstly, it has to be taken in account that each constellation may be seen as a ”body” rotating around a fixed hinge - the Polaris - and, each day, runs a complete lap around the above mentioned hinge.

If the Sun burnt out, it would be possible to observe, at any time of the day, the rotation that constellations make around the Polaris; hence, we may be allowed to identify, without having to wait for the night, which constellations are visible and which are not, depending on the hemisphere we find ourselves in. Moreover, there are some constellations far from the Polaris in terms of angular distance onto the celestial sphere, so it may happen that these, although visible for a few hours during the night, are not actually observable, because, whilst spinning, overcome the observer’s horizon ending up in the celestial sphere’s opposite hemisphere.

On the other hand, as far as star signs are concerned, it must be taken in account that the Sun, during the year, seems to be running an apparent path (which creates the ecliptic’s plane), not equivalent to the Equator, but inclined of a few degrees. This is why, throughout the year, the Sun ”darkens” (that is Celestial map of the European sky in June. to say, making them not visible because of too much light) some parts of the sky, while running on its own apparent path.

Other than the mentioned reasons, it must be said that two observers in different parts of the Earth, do not see the same sky, which basically depends on their different longitude/latitude and, moreover, on the Earth’s non-spherical shape, which means that an observer on the Earth’s surface is able to observe only a portion of the celestial sphere, strongly bordered by the horizon.

Towards the end of this stellar journey we must know that the sky has always been fascinating human beings, changing their technological progress (let’s just think about sea navigation, based on the Polaris) and humanistic (there are countless works inspired by the celestial sphere’s observation). Hence, we do owe a lot to the sky above our heads and a proper observation of this infinite, extra-terrestrial environment above us must help us get to better know ourselves, our history and, unavoidably, our future.

References for “The Constellations and the Zodiac.” - May 2012 in Italy http://www.planetariodanti.pg.it/starlab/lavori/eclit.html http://it.wikipedia.org/wiki/Costellazione http://it.wikipedia.org/wiki/Sfera_celeste http://it.wikipedia.org/wiki/Triangolo_estivo http://it.wikipedia.org/wiki/Portale:Astronomia/Cielo_del_mese/Panoramica_giugno http://it.wikipedia.org/w/index.php?search=Carta+celeste&title=Speciale%3ARicerca http://www.trekportal.it/coelestis/showthread.php?t=26506 http://www.parodos.it/storia/argomenti/le_costellazioni.htm http://www.lavocedellestelle.com/info/osservazione-costellazioni.aspx http://www.mogi-vice.com/Pagine/Scaricamento.html http://www.parodos.it/im3/ZODIACO_09SenNom.jpg http://anniluce.files.wordpress.com/2011/05/il-cielo-di-giugno.jpg http://www.planetariodanti.pg.it/starlab/lavori/images/eclit_clip_image002.jpg http://www.mogi-vice.com/Pagine/Scaricamento.html

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Lift off of Space Shuttle Atlantis.

How do Rockets fly?

Written by Udrivolf Pica Student of Space Engineering Translation by Claudia Alvarenga

“Actioni contrariam semper et aequalem esse reactionem”. In other words: for every action there is an equal and opposite reaction. The above mentioned is the Third Law of Dynamics (or Principle of Action and Reaction) and rules the nature of every phenomenon around us : it is what allowed us to conquer space and send rockets and first humans in orbit.

Commonly, the word “rocket” is synonymous of “something complex”.

Actually, these mysterious and fascinating objects are nothing less but an application, though refined and very powerful, of the above mentioned principle of action and reaction.

Now, let's try to understand, briefly, how this principle is able to make a space vehicle (that is, a rocket) lift up. To do so, let's introduce a technical term, synonymous of rocket : “Endoreactor”. The word is itself clarifying : “endo” (meaning inside, on board) and “reactor” (which involves the principle of action and reaction). A rocket, thus, is so defined because, being required to operate also in cosmic vacuum, carries on board whatever it needs to fly, which is not simple at all; as if airplanes or cars were supposed to carry on board air from outside, other than fuel.

A common example of an endoreactor is given by fireworks. In these, once we fire the fuse, the flame reaches the gunpowder and, after a very short explosion, we see the fireworks quickly lifting up. Chinese were the first in history to develop these objects and, without knowing their basic working principles, they began to refine them in order to take advantage of them, especially in wars.

However, it is not until the second half of 1800 that Russian scientist Konstantin Eduardovich Tsiolkovsky (1857 - 1935) laid the basis of theory of endoreaction.

Leaving out several mathematical formulas related to this theory, let's now try to understand the origin of the “force” (historically called “Thrust”) that lets us overcome atmospheric drag and the pull of the Earth's gravity, the only two forces holding the rocket (and any other body) stuck onto the ground.

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At first, it is useful to observe that stowed inside a rocket there is the propellant, which is the “fuel” required for our mission. The weight of the propellant can reach up to 95% of the total weight... and we are dealing with several tons. Now, it is clear that to light up hundreds of tons of propellant (which may be liquid or solid, depending on the rocket's mission) a fuse used for fireworks is not powerful enough. Generally speaking, it is necessary to induce a controlled explosions, which provides energy required to activate the complete process of ignition (i.e. “lighting”).

Exploded view of Atlas V rocket.

Mission profile of Atlas V rocket.

Rocket propellant is a mixture of fuel (basically similar to oil in our cars) and oxidant (which, in a street vehicle, is the air entering the engine from the outside through appropriate intakes); these two, mixed up and burnt in proper ratios, produce thermal energy, that is, they release heat (temperatures inside a rocket engine might even exceed 3500 grades).

By this point, a question arises: how to manage a mass of hot and high pressured propellant through the whole process of draining, so that it will flow outside of the rocket, releasing all of its “force” (meaning its Action)? The drain pipe, called nozzle, if properly built, that is if made of a convergent and then divergent section, is the element that helps us, letting the burnt gases achieve very high velocities, in the order of magnitude of 4000 m/s.

Hence, thrust is generated when thousands of particles of burnt propellant are exhausted from the rocket at very high velocities. This flow (called “propulsive flow”) responds with a force, equal and opposite to that by which it's been accelerated, acting on the internal walls of the rocket and allowing it to lift up.

Concisely, it's like when we put a hand on the table: it supports us by responding with a force equal and opposite to the one we applied. Such is the working principle of a rocket: we provide energy to the fluid by means of an acceleration in a chosen direction, so it exerts a force opposite to the direction of the wall of the nozzle : such a force is conveyed to the whole structure and, if intense enough to overcome gravitation and atmospheric drag, the lifting takes place.

It's worth observing that Thrust may be obtained in several ways; that just described works for most common rockets: chemical thermal rockets, whose primary source of energy is chemical, contained in fuel and oxidant.

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ESMI- #1 Once the rocket has left the ground, in order to keep ascending, it has to constantly counteract perturbations (atmospheric drag and gravity).

Atmospheric drag becomes negligible at 200 km above the ground, where atmosphere is so rarefied that its drag (that is to say, the force of air particles onto the rocket structure) is basically zero.

On the contrary, gravity is overcome by properly using its balance with centrifugal force. The rocket's acceleration, during its ascent, is constantly increasing, and so is its velocity. When the rocket's velocity is about 8000 m/s, that is 8 km/s, the centrifugal force of the rocket orbiting the Earth balances gravity. This balance allows the satellite (carried onboard), released and dropped into space, to stay in orbit and accomplish its mission.

Clearly, if we don't stop at 8 km/s but keep accelerating, the rocket will move to further orbits and, eventually, escape Earth's gravity, covering an interplanetary trajectory.

Lift off of Ariane 5.

At last, there's one more “mystery” to be solved by this point: why, every time a rocket takes off, does it “lose” some pieces? This is what's called “staging” and it's rather simple to explain: it's been said that the minimum velocity for an object to orbit Earth is about 8 km/s; it is proved by mathematical formulations (which we are omitting) that it is not possible to reach that velocity with a single engine.

This is why several endoreactors, called “stages”, are set up one above or parallel to each other and, once the propellant is burnt, they are dropped out in order to make the structure less heavy. An example of a staged rocket is European Space Agency's (ESA’s) Ariane 5, one of the biggest rockets on the market.

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Soyuz going to the launch site.

It's been briefly explained how rockets fly, but many other topics need to be faced, since rockets are the most powerful and complex objects ever built by human beings. We are all fascinated by the power exhausted in such a short time lapse, which must be controlled without making mistakes.

The rise of a rocket is always a wonderful event, capable of exciting the lucky spectators, who can easily understand that (as stated by American Engineers) “the only thing rising above the noise of the rhetoric is the roar of a launch”.

Lift off of VEGA (Vettore Europeo di Generazione Avanzata).

References for “How do Rockets fly?” - May 2012 in Italy

Dispense del corso di “Propulsione Spaziale” tenuto dal prof. Di Giacinto, Professore Ordinario di Ingegneria Spaziale presso l’Università di Roma “Sapienza”.

Immagini: Portale ESA, Portale ULA, Portale NASA.

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How does the Satellite Navigation System work?

by Matteo Sciarra Student of Space Engineering Translation by Luca Nardini

Ever since the old times, one of the problems of mankind has been orientation. Just think about those who set off for a journey over unexplored oceans or toward new and endless lands. Getting lost meant not to be able to go back home or worse! Being able to read a map, a compass or knowing the stars was therefore fundamental. Nowadays things have changed because we can buy a portable GPS that can give us our exact position on the planet at any time.

How does the GPS (Global Positioning System) work? What technology lies behind it? And how is the device's position determined?

The GPS is an extremely precise terrestrial positioning system created by the US government for military purposes whose use was later extended also to civilians.

The GPS is linked to 31 satellites that form what is called “satellite constellation�. They have a round orbit, on 6 different orbital planes, with an inclination of 55° degrees over the equator. Every satellite's altitude is around 26,560 km and they round the Earth twice a day (the time elapsed for a revolution is 11 hours and 58 minutes). The satellite's orbits are set so that every spot of the Earth is covered by at least 4 satellites at the same time.

Apart from the satellites, the GPS also requires 4 control stations on Earth whose task is to constantly verify the satellite's status and correct their atomic clocks and orbital position. Without these stations the GPS would not be able to function.

Repairing cycles must therefore be constant. It has been calculated that a suspension of these cycles would cause a fast functional decadence in a few days and a total collapse of the system after about two weeks.

GPS satellites are equipped with: antennas (a reception and emission system from and to Earth or to other satellites), many oscillators and highly precise atomic clocks (to guarantee the correct functioning of at least one of them), small engines (to correct their orbit), two 7,25 square meter solar panels (for energy production), and emergency batteries (to guarantee energy supply in absence of solar light). Every satellite has a mass of around 845 kg and an estimated lifetime of 7,5 years, after which it has to be replaced.

Artistic representation of the GPS constellation.

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ESMI- #1 Anyway, as far as satellite navigation is concerned, the majority of work is done by the GPS receiver (the one we buy), that executes the following operations: localization of at least 4 satellites, calculation of the distance from each satellite and use of such data to calculate its position though the triangulation process and comparison of maps.

A satellite of GPS constellation.

The triangulation is the method used to calculate your position. We will now see how it works in the following example, using a bi-dimensional space to make it easier to understand.

Even though the GPS works in a tridimensional space, it uses the same concept.

Let's imagine we are lost and we want to know what is our location. We ask for help to a bystander who tells us: “You are at exactly 215 km from Naples”. We can show this piece of information in this way:

Common GPS portable devices.

Satellite GALILEO after its launch.

If Naples is in the center, it mean that our position can be in any point of the circumference whose center is Naples and whose radius is exactly 215 km.

Now we meet another bystander that give us another piece of information: “You are exactly 271 km from Florence”. Showing this new information, we would have this situation:

Taking into account the two pieces of information, we are sure that we are at a point 271 km away from Florence and 215 km away from Naples. As can be seen in the picture, only two spots (the blue ones) suit the description.

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GALILEO navigation satellites in the Soyuz.

To understand in which one of the two spots we actually are, we therefore need a third piece of information. Luckily we meet a third bystander that tells us: “You are exactly 80 km from Rome”.

Now we can finally determine where we are without any doubts: the only point in the world that is 271 km away from Florence, 215 km away from Naples and 80 km away from Rome (which is a small city called Rieti).

Obviously, all this can work only if we know the exact location of Naples, Florence and Rome. In reality, as we have already said, the calculation takes place in a tridimensional space (thus making 4 measurements), so instead of circles, we must imagine spheres that intersect until they determine a single spot. Theoretically, 3 measurements from 3 satellites would be sufficient to determine our position, since the fourth measurement would be replaced by the fact that we know we are on a point on the Earth surface, which represents the fourth sphere. Four or more satellites are used at the same time to improve the system's precision.

Calculate the distance.

Taking the previous example into reality, we would have a GPS receiver that determines its distance from the satellites and with this data it immediately calculates its exact location. To determine the distance between the device and the satellite the GPS measures the time that a signal takes to reach Earth. This process may seem easy, but actually there are a lot of complications. Here is how the measurement is done: at a prefixed time (for example 12 am) the satellite generates a signal that is sent to Earth. Also the GPS receiver generates the same signal at 12 am so that when the one sent by the satellite is received by the GPS, it acknowledges it and through a series of confrontations is able to measure how much time took the signal to arrive from the satellite. By multiplying the result by the speed of light (300,000 km/s) we obtain the distance between the GPS device and the satellite.

The calculus itself is rather simple. All we need to know is the exact moment when the signal was sent from the satellite. We must be extremely precise, since even a difference of a thousandth of a second can penalize the measurement, causing an error of 300 km! To ensure the necessary precision, every satellite is equipped with four extremely expensive atomic clocks (each costs around 160,000 €) that use the oscillation of cesium and rubidium atoms and guarantee absolute precision (the possibility of error is only one second every 30,000 years).

It is obvious that in such a precise system, also the receiving device must guarantee a high level of performance. Taking into account that a portable device cannot be equipped with 160,000 € worth-atomic clocks, scientists have decided to use clocks that can be extremely precise only for a short period of time, that are often corrected using the signals sent by the satellites.

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ESMI- #1 Precision of the GPS. The GPS system is available in two versions: PPS (Precision Positioning Service, for military use) and SPS (Standard Positioning Service, for civil use).

Extra

According to official data, the PPS system has an accuracy of 6-20 meters. The SPS system could have the same performances if it was not for the so called “selective availability”, which is an “error” in the measurement caused by the Ministry of Defense of the USA. Practically, the accuracy of the clock is intentionally modified, which has a negative effect on the precision, that has therefore an accuracy of about 100 meters. However, such degradation of the signal has been disabled in May 2000, thus allowing civil devices to have the current precision of about 10-20 meters. On the other hand, civil devices have other limitations, such as an 18 km maximum altitude and a maximum 515 m/s speed to avoid the installation of this device on missiles.

Alternative Systems: GLONASS e GALILEO. These two positioning systems have been created respectively by Russia and the European Union to stop the American monopoly and avoid the precision limitations of the GPS system.

The European system will have a better precision than the GPS system and many more advantages. The system is expected to be available by 2014 and will be sustained by 30 satellites on 3 plans inclined over the equatorial plan, at an altitude of around 24,000 km.

References for “How does the Satellite Navigation System work?” - May 2012 in Italy

http://www.comefunziona.net/arg/gps/ http://it.wikipedia.org/wiki/Global_Positioning_System http://en.wikipedia.org/wiki/Global_Positioning_System http://it.wikipedia.org/wiki/Sistema_di_posizionamento_Galileo http://it.wikipedia.org/wiki/GLONASS http://media.defenseindustrydaily.com/images/SPAC_GPS_NAVSTAR_IIA_IIR_IIF_Constellation_lg.gif http://upload.wikimedia.org/wikipedia/commons/9/96/Global_Positioning_System_satellite.jpg http://upload.wikimedia.org/wikipedia/commons/5/59/GPS_Receivers_2007.jpg http://www.comefunziona.net/arg/gps/3/ http://www.aviationnews.eu

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