Yearbook 2017 sampler by Immediate Media Company London Ltd.

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PRACTICAL ADVICE TO GET MORE FROM YOUR KIT

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Your handbook to the best stargazing from January to December

SEASONAL TARGETS FOR SCOPES AND BINOCULARS

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YEARBOOK

EXPERT GUIDE TO FASCINATING ASTRO IMAGING PROJECTS SOLAR OBSERVING

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THE BEST SCOPES OF 2016 REVIEWED

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HOW TO FIND THE NEXT SUPERNOVA

TAKE BETTER ASTROPHOTOS FROM UNDER CITY SKIES

IMAGING UNDER

CITY SKIES Jaspal Chadha reveals how you can capture quality deep-sky images under light-polluted skies

or the last few years I’ve been taking images of the night skies. But there’s a problem: I live in London, one of the most light-polluted areas in the UK. This makes it hard to achieve one of the main requirements for a good astro image – a high signal to noise ratio. While the best way to increase that ratio is to reduce the noise by imaging from a site with darker skies, there are various things you can do to capture decent images from under the urban lights in the middle of a city. After months of trial and error I finally settled upon a setup that works for me. When I started I used a DSLR and colour single shot CCD. The results weren’t what I expected. The images lacked detail and were often filled with the orange glow of light pollution, despite my best attempts to reduce it. Even with exposures of four hours I wasn’t happy with the amount of detail being captured and trying to remove the glow with photo-editing software was a long process that still didn’t get me the results I wanted.

Sacrifice colour for clarity Things improved when I switched to using a monochrome CCD camera, an option that retains the main advantage of a CCD: its sensitivity. The more sensitive the camera, the shorter the exposure

If you live in the city, the full Moon is far from the only source of irritating sky glare – but it’s possible to capture wonderful images all the same

required to detect faint detail. CCD cameras have a greater dynamic range than DSLR cameras, meaning there’s a larger range of luminosity that they can detect. The CCD can more easily capture both faint and bright detail in a single exposure, rather than needing several images to bring out different elements. However, a mono CCD only detects the brightness of the light, not its colour. If you want to bring out the colour of images you have to use filters. In normal colour imaging, three filters are used to separate the primary colours of the visual spectrum. Red, green and blue (RGB) filters are designed to approximate the colour sensitivity of the human eye, so that the resulting image is true colour. When using RGB filters to create a broadband image, all types of wavelengths are captured across the entire visible spectrum so this picks up a lot of light pollution from the surrounding

“My images lacked detail and were often filled with the orange glow of light pollution”

IMAGING UNDER CITY SKIES 2017 city lights. This is usually most visible as green and magenta gradients in the images. To reduce this I use a simple CLS CCD light-pollution filter. There are a few things to remember when using light-pollution filters, however. First is that they’re not 100 per cent foolproof when it comes to light suppression. These filters are helpful, but they have their drawbacks. All of them are designed to block out only particular wavelengths of light and there’s one overriding factor to consider when deciding how effective they’ll be for you. They’re designed to block the wavelengths emitted by low-pressure sodium-vapour lamps – the orange type. If the location where you make your observations from is lit by newer LED street lamps, then light-pollution filters will be useless. They also cut down the total light getting to the sensor, so the exposures required will be longer. But they should increase the ratio of useful image information compared to background glow, so overall should result in an improvement.

Jaspal’s setup: switching to a mono CCD has made all the difference under the light-polluted London skies

Go deeper by narrowing down

Much time and effort will be required to capture data from all three filters. So little light gets past the filter that imaging requires very long exposure times. Typically I’ll spend at least three to four hours’ imaging time on each filter, with some single exposures of up to an hour. The most rewarding results come from the Ha filter. The image is readily visible and has much detail. The OIII and SII filters produce dim, noisy images that are frustrating to work with, but are needed for a complete image.

Staying on target Keeping the telescope on track when narrowband imaging takes some practice too. I use an autoguider, and finding a stable guide star can be a challenge thanks to the fact that so little light reaches the >

For those times when I want to bring out the finer detail of a deep-sky object, I attach narrowband filters: the light-pollution filter’s green tint is easy to remove in photo-editing software during the image-processing stage. These filters enhance the contrast of emission objects by accepting only a narrow range of wavelengths around the emission lines of certain gasses within the objects, such as hydrogen-alpha (Ha), doubly ionised oxygen (OIII), ionised sulphur (SII) and others. During the image-processing stage, data from each emission line is assigned a certain colour band – red, green or blue – and these are combined later in a graphics editor to create the most stunning images. As narrowband filters only pick up a tiny portion of the available light, they can be used to take astrophotos even when the Moon is up as well or from locations that are usually plagued by light pollution. Narrowband filters commonly come with a bandwidth of 5nm or 3nm at the emission line they let through; you can expect to pay a higher price for the lower bandwidth filters.

Þ The night sky before (left) and after (right) processing – the amount of sky glow that can be removed with editing software is tremendous WWW.SKYATNIGHTMAGAZINE.COM

JANUARY 2017

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MOON PHASES Key stages in the monthly cycle

CONSTELLATION NAME GALAXY OPEN CLUSTER

NEW MOON 28 Jan

LAST QUARTER MOON 19 Jan

STAR NAME

GLOBULAR CLUSTER PLANETARY NEBULA DIFFUSE NEBULOSITY DOUBLE STAR

VISIBLE PLANETS Where to spot the planets this month

VARIABLE STAR THE MOON (SHOWING PHASE) COMET TRACK ASTEROID TRACK

MARS

An evening planet in Aquarius, appears 20 arcminutes from Neptune on 1 Jan

JUPITER

A morning planet in Virgo with the Moon nearby on the morning of 19 Jan

SATURN

A morning planet in Ophiuchus with the Moon nearby on the morning of 24 Jan

URANUS

An evening planet in Pisces best seen at the start of Jan around 18:30 UT

NEPTUNE

An evening planet that has an apparent close encounter with Mars on 1 Jan and Venus on 12 Jan

STAR-HOPPING PATH METEOR RADIANT et

VENUS

A bright evening object that reaches greatest eastern elongation, 47.1° from the Sun, on 12 Jan

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Well placed in the morning sky, reaches greatest western elongation of 24.1° on 19 Jan

PETE LAWRENCE X 3

MERCURY

ASTERISM MILKY WAY PLANET STAR BRIGHTNESS:

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JANUARY 2017

JANUARY at a glance Meteor showers and comets get the year off to a dazzling start Comet 45P/Honda-MrkosPajdusakova traces a path across our sky early in the year

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SAGITTARIUS CAPRICORNUS Antares

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star Rigel in the southwest corner and bright orange Betelgeuse in the northeast corner. Extend a line from Rigel through Betelgeuse for almost twice that distance again to arrive at a pair of similar brightness stars known as Castor and Pollux, the two main stars of Gemini. Look closer and you’ll see that Castor is Lunar phase Plough

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he January night sky is full of splendour with mighty Orion well placed before midnight. The Hunter’s main pattern is unmistakable thanks to the straight line of three stars that form his belt. Follow the belt up and you’ll arrive at orangeKEY TO coloured Aldebaran, the brightest star in Taurus, the Bull. STAR CHARTS The V-shaped pattern of stars nearby is the Hyades open cluster. Continue the belt line through Aldebaran to reach the Pleiades, or Seven Sisters, open cluster, which is also part of Taurus. If you extend the arms of the Hyades, you’ll reach two middle-brightness stars representing the Bull’s horn tips. The lower star is Zeta (ζ) Tauri. M1, the Crab Nebula, lies 1.1° northwest of Zeta and requires a telescope to see it at its best. The northern horn-tip is marked by Beta (β) Tauri, or Elnath. Charts often show Elnath connecting Taurus to the misshapen pentagon of Auriga, the Charioteer, which lies to the north. This is because Elnath used to belong to Auriga before getting a transfer to Taurus. The brightest star in Auriga is the yellow sun Capella, which sits on top of the ‘pentagon’. Return to Orion and marvel at the difference between the bright white

Þ The Quadrantid meteor shower hits it peak in the first week of January

slightly dimmer than the more orangehued Pollux. Castor and Pollux define one short side of Gemini’s rectangular shape, which extends back towards Orion.

Comets and meteors Heading south from Pollux you’ll reach solitary Procyon, the brightest star in Canis Minor. There’s not much to the rest of the constellation apart from Beta (β) Canis Minoris, or Gomeisa. Canis Major can be found by extending the Belt of Orion southeast towards Alpha (α) Canis Majoris or Sirius, the brightest star in the night sky. Eight apparent full Moon diameters (4°) south of Sirius is the lovely open cluster M41, which may just about be visible with the naked eye on a cold, dark January night. Keep an eye out for Quadrantid meteors at the start of the month. The shower’s activity rises to a sharp peak during daylight on 3 January so the best time to watch will be on the nights of the 2/3 and 3/4 January. Another January highlight will be the appearance of binocular comet 45P/Honda-Mrkos-Pajdusakova visible in the evening sky at the start of January around magnitude +7.1, but switching to the morning sky by the end of the month when it will be around magnitude +8.

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LONG-TERM PROJECTS 2017

Þ The oval Mare Crisium in the upper right changes position relative to the Moon’s eastern limb due to libration

SHOWING LUNAR

LIBRATION

Pete Lawrence shows you how the rocking and rolling of the Moon allows you to see around its sides

PETE LAWRENCE X 7

us and fastest when it’s closest. he Moon is the The plane of the Moon’s Earth’s nearest RECOMMENDED orbit is also inclined by neighbour in approximately 5° to that space and of the Earth’s orbit both orbit a common Any setup that’s capable around the Sun. centre of gravity, or of capturing the entire disc Taken together, these barycentre, which of the Moon and showing effects allow us to see lies 1,700km below the main features of the a bit more of the Moon the Earth’s surface. lunar surface, such as than we should. The Over time the Moon’s the dark seas and larger craters. speed variation allows us rotation period has to peek around the eastern synchronised with this orbit and western edges of the Moon causing it to present the same, while the inclination allows us to glimpse battered face to us throughout around the northern and southern edges. the lunar month. Well nearly… This rocking and rolling is known as The orbit is elliptical so the Moon’s libration and its effects, when combined, distance from us is constantly changing allow us to see a total of 59% of the along with its speed. This is slowest when Moon’s surface. the Moon is at its furthest distance from

100

EQUIPMENT

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Features really close to the edge of the Moon are described as being within the libration zone. When libration is favourable for them, they can be seen with reasonable clarity. When libration is unfavourable, they won’t be visible at all. Catching a good look at a feature in the libration zones is harder than you might think. Obviously the libration needs to be favourable, moving the feature closer to the centre of the Moon’s disc. Then the phase has to be right. It’s no good having favourable libration for a feature if the phase means it can’t be seen. On top of this, the weather also has to play ball to allow you to see the favourable phaselibration window. There are various ways to see what libration will be evident on a particular date. For example, the excellent Virtual Moon Atlas (www.ap-i.net/avl/en/start), has this capability. You can see and illustrate the effects of libration by imaging the Moon’s disc over as many consecutive nights as possible, then creating an animation from the results. The vagaries of the UK’s weather mean that many sequences will be interrupted, but it’s surprising how short a window in cloud you need to actually catch the Moon – so it’s worth being tenacious! Try to capture as many sequences as you can throughout the course of the year and then use the longest for your animation.

M ER -T G G IN N AG LO IM

Create an animation to see more of the Moon

Grimaldi WORSE

✗

Mare Crisium

✓

BETTER

STEP 1

This project is suitable for a setup that can record a full lunar disc while also showing a reasonable amount of detail; Mare Crisium and crater Grimaldi are the bare minimum. A focal length of 400mm or longer is recommended. Full-disc shots make life easier but mosaicing highermagnification images to cover a full disc will work too.

STEP 2

It’s important to keep the same orientation between shots. If you’re using an equatorial mount, place the Moon in the field and slew back and forth in RA. Carefully rotate your camera so the Moon moves parallel to the upper and lower edges of your image frame. Once done, your camera will be aligned to the RA-Dec coordinate system.

✗ STEP 3

Choose the terminator region as the focus target and focus as accurately as possible. Here the stark shadows and highlights really help. If your camera allows, zoom in to make sure your focus is really sharp. Even when the Moon is full, there should still be a very thin terminator visible right on the edge.

STEP 5

CT JE O PR

STEP-BY-STEP GUIDE

Load a completed sequence into a layer-based editor, one image per layer and in date order. Make all layers invisible except the bottom one. Make the next layer up visible and align with the bottom layer so the disc centres correspond exactly. Repeat this process for all the layers, aligning each one to the layer immediately below.

✓

✗

STEP 4

Adjust the camera’s sensitivity and exposure to give you a correctly exposed image of the Moon. Avoid white-outs (over-exposure) or black regions on the disc (under-exposure). For DSLRs, keep the ISO relatively low, 100-200 for example. For non-tracking setups, use a higher ISO and shorter exposure to avoid motion blur.

STEP 6

There are various ways to create the animation. Photoshop, for example, has a ‘timeline’ feature that lets you create animation frames with each layer. Alternatively, save each one in a lossless format such as TIF and load them into the freeware PIPP application (sites.google. com/site/astropipp) from where the animation can be created.

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101

ED SPE IT CIA IO L N

YEARBOOK

2017

FROM THE MAKERS OF

ONLY £9.9&9P*

Explore the night sky over the next 12 months with BBC Sky at Night Magazine’s Yearbook 2017. This indispensable astronomy bible contains a full year of stargazing tips, projects and how-to guides, amazing images and dates for all the astronomical events you can’t afford to miss; plus detailed monthly star charts to guide you to the best views. Plus – subscribers to BBC Sky at Night Magazine receive FREE UK P&P*!

All the key dates for your diary to help you keep track of eclipses, oppositions, occulations, meteor showers and more

INC P

Photography projects to help you make a record of sky phenomena, with guides to locations, camera settings and editing

Expert advice on finding and observing deep-sky objects with the naked eye, binoculars, and small and large scopes

ORDER YOUR COPY TODAY www.buysubscriptions.com/yearbook2017 Alternatively call 0844 844 0254 and quote ‘SKYBHA17’ †

†Calls will cost 7p per minute plus your telephone company’s access charge. Lines are open 8am-8pm weekdays & 9am-1pm Saturday. *Subscribers to BBC Sky at Night Magazine receive FREE UK POSTAGE on this special edition. Prices including postage are: £11.49 for all other UK residents, £12.99 for Europe and £13.49 for Rest of World.