L-Għaqda Maltija tal-Astronomija

Stepping into astronomy

by Ramon Casha

Astronomy is a very fascinating field of science, and nowadays is more accessible than ever to amateurs. Equipment for astronomy can be very expensive, and one thing you should avoid is to jump in with your credit card and buy equipment then realise it’s not what you needed. You can enjoy astronomy with very little cost, and gradually buy things – if you need to – to help you in your chosen fields of science. This article is an introduction to astronomy that will hopefully help you avoid expensive mistakes.

One good way to start of course is to join up with others who share the same hobby. You’ll be able to gain from their experience, see how different equipment is used, and the pros and cons of each, and so on.

If you ask me what’s the most important thing to have to make some good observations, I’d choose a dark place. A very, very dark place. There’s a reason why all the big, professional observatories are built in really remote places at the top of a mountain somewhere – the darker the area, the more you will see. If you look up at the night sky from the middle of a city, sometimes all you’ll see is a few dozen bright stars. You have to move away from cities, road lighting, lit buildings and so on. The difference this will make is amazing. From a properly dark place, even with the naked eye, you can see over 4000 stars – so many that even familiar constellations can suddenly look unrecognisable with all the extra stars. You can see the Milky Way as a cloudy band across the sky. You can see the faint fuzzy shape of the Andromeda galaxy – the furthest thing you can see with the naked eye at 2.5 million light years distance. You should ask other astronomers about dark places to observe from. In Malta, the darkest places are Miġra l-Ferħa, Fomm ir-Riħ, some spots along Dingli Cliffs, as well as L-Aħrax tal-Mellieħa, and Dwejra in Gozo. In some places along the coast you can see quite well in one direction, and less well in others – for example you can get a good view of the North-East from Pembroke coast.  Have a look at our ‘Malta at night’ overlay which you can see at http://www.maltastro.org/light-pollution.

You can zoom in and out, change the opacity of the photo layer (slider top right) and switch the base image between a map and a satellite daytime photo.  The original image is an image shot in October 2013 by astronauts on board the International Space Station.

Of course, you also need to choose a dark night – that means a moonless night, and as clear a sky as possible. A few clouds here and there usually pose no problems – you can wait for a cloud to move past – but a haze covering all the sky will severely limit observation. You can get a pretty good idea of the clarity during the day by looking at a distant place – it can appear clear or covered in haze. A cold, clear, moonless night usually gives best clarity. Note that a moonless night doesn’t necessarily mean a new moon – you can also choose a night when the moon doesn’t rise until early morning, or sets soon after the sun. There are apps and websites that tell you what time the moon rises and sets.

For your first observation, try without any astronomical equipment at all – just use your eyes. Some non-astronomical equipment will help a lot however. First – either a comfortable chair or a mat to lie on the ground will save you from spending a lot of time craning your neck upwards. Next, dress up warm. A cold night gives great clarity but if you’re going to spend a few hours, possibly with some dew, you’ll get cold quickly. It’s better to have too much and be able to take something off, than shivering as you observe. Sometimes even in summer it’s good to have long sleeves, and a flask of something hot works wonders. I find that a pair of fingerless gloves is useful to allow you to manipulate equipment while keeping warm. A note about summer – you will probably be the most delicious thing in the area to mosquitos. Again, long sleeves and pants will help keep you off the menu, but you might also want to pack some mosquito repellant.

The only “specialised” thing you need to take with you is either a printed star chart, or a smartphone app that shows you the sky “live”, such as Google Sky Map. There are a number of websites from which you can print a star chart, such as skymaps.com. If you take a torch with you to look at the star chart, fit it with a red filter – a piece of red transparent plastic will do. Our eyes take time to get used to the darkness, and you don’t want to lose that night vision every time you turn on the torch to look at your star chart. Red light is best suited to ensure you retain your night vision.

There are many things to observe with the naked eye, plus it’s very useful to familiarise yourself with constellations, since these serve as landmarks (or is it skymarks?) by which to find other objects. You can find the North Star, Polaris, by following a line from two of the stars in the Big Dipper. You find the Great Nebula by first finding Orion, and you can find the Andromeda Galaxy by first finding Cassiopeia. Of course one of the best naked-eye objects is the Milky Way – our own galaxy. Try to match what you’re seeing on the star chart with what you’re seeing above you. Enjoying the night sky like this from a dark place can be quite an experience.

Finding PolarisFinding PolarisFinding the Andromeda GalaxyFinding the Andromeda galaxy (M31)

Finding the Orion Nebula

Finding the Orion nebula (M42)

Since the earth is orbiting the sun once a year, that means that the side facing away from the sun – our night – also changes over the course of a year – and the objects visible in the sky change too. The Milky Way is at its most magnificent in summer. That’s when the night side of the earth is facing the centre of our galaxy – the brightest part. On the other hand the Orion nebula is most visible in Winter. That’s why star charts vary from month to month.

Next thing you could do, if already you have any telescope or binoculars, is to try these out on the same objects.

Telescopes serve two purposes in astronomy. One is to magnify small objects, and the other is to make large but faint objects visible. For instance, the Andromeda Galaxy appears about six times the diameter of the moon as seen from earth – but is so faint that only the thickest part is just about visible from a dark place.

Magnifying objects is the easy bit. You just apply different lenses and it magnifies the image. One easy target is our moon – look at it when it’s a crescent and you’ll see craters and mountains along the crescent edge. That’s where the shadows are at their starkest. By comparison the full moon will seem rather flat and uninteresting.

As you increase magnification, you will also be magnifying every little shake of your hand. You can see things with small, handheld binoculars but ideally you’ll find a steady place where you can rest your elbows, or a tripod.

Making faint objects visible is where astronomical telescopes differ from regular terrestrial telescopes. Actually there are two ways of making faint objects visible. One is to use a camera. Cameras have a couple of “features” that our eyes don’t have. One is the ability to take a single picture using several minutes’ worth of light. If you take a regular camera which has the ability to take long exposures, place it on a tripod, point it at the Milky Way and leave it open for several seconds, you’ll see some great details that are not visible to the naked eye. The other difference is that, when the light is dim, our eyes switch to black and white. That’s why, in the moonlight everything appears grey. Cameras don’t do that. They always see in colour, and when you take a photo of something that appears grey to our eyes – even through a telescope – a camera will produce bright reds, blues, violets etc.

The second way of making faint objects visible is via the telescope. The wider the telescope, the more light it will gather and concentrate into the eyepiece. They won’t appear any bigger, just brighter. Of course, the wider the telescope, the bigger and heavier (and more expensive) it will be – so there’s a trade-off between a telescope that gives you good viewing, and one that’s so heavy that you can’t be bothered to take out to a dark place.

A telescope is composed of two main parts – the tube itself, containing the mirror and/or lenses, and the mount, which is the tripod or other stand on which the telescope is mounted. The mount can be as important as the tube for serious astronomers, as I shall explain.

Due to the differences that I mentioned between our eyes and a camera, choosing a telescope and mount depends a lot on whether you want it for astrophotography or for visual observation.

For visual observation, the wider the aperture of the tube the better – though they’ll also be bigger, heavier, bulkier and more expensive. The tube will be set on a mount, which is usually either a Dobsonian mount or equatorial mount. Many mounts nowadays offer the option of a small, handheld computer called a GoTo controller. Once you align the telescope to two or three different stars, the GoTo controller can calculate the position of any other object in the sky and point the telescope to it directly. Finding stars “manually” is fun too but many people find it more convenient to let the controller do the work – of course this comes at a price since the mount has to be motorised.

The magnification of the telescope is changed by switching the eyepieces. Many telescope “kits” come with a handful of eyepieces. The larger the number, the lower the magnification. I use a 40mm eyepiece as a very low magnification (but very wide field of vision) eyepiece to find objects or to look at large objects, then switch to a 25mm, 10mm or even 5mm eyepiece to get better magnification once the object is centered. The greater the magnification, the narrower the field of vision, the more shaky the image will get, and the clarity will also begin to fall.

For astrophotography, it’s more important to have an extremely good mount that can keep an object in the dead centre of the field of vision for several minutes. You might not see them move, but the earth is constantly rotating so the stars appear to be moving. You can actually see them move in a telescope, slowly creeping from one side of the eyepiece to the other. In a photo that would appear as a line. An Equatorial Mount is a specialised mount in which the axis of the mount is exactly parallel to the earth’s axis, so that by rotating the mount in the opposite direction at the same rate, the telescope is kept pointing at the same point in the sky. The more precise and smooth the movement of the mount, the better the quality of the photo produced. It’s quite common to have a mount that’s more expensive than the telescope mounted on it.Of course for astrophotography you also need some kind of camera. One can use either a regular DSLR camera, a dedicated CCD camera or a webcam. If you already have a DSLR camera you can easily buy an attachment that fits in place of the lens and allows you to fit the camera instead of the eyepiece. There are inexpensive webcams you can use – usually you’d remove the webcam’s front lens and attach the webcam instead of the eyepiece. Dedicated CCD cameras are expensive and beyond the scope of this article.

I hope that this gives a good idea of how to go about starting astronomy. It’s a rewarding hobby which not only has an ever-changing fantastic display in the sky, but also provides the occasional special treat in the form of a meteor shower, a comet, a supernova or other phenomena. Astronomy is also the discipline through which we learned a lot about ourselves – our small place in a vast universe, humbling yet inspiring, amazing and peaceful.

Clear skies!