Phil's Astronomy Amateur Page

I've been in and out of astronomy over the years and now I'm back 'in' - it's a bit like Sunspot cycles, really! Now I'd like to share development of it with you.

Wednesday, 25 February 2009

Phil's Astronomy Beginners

Introduction
Ever since I was a little kid I remember looking up at the night sky and being able to recognise certain obvious constellations like Ursa Major (Big Dipper/Big Bear), Ursa Minor (Little Bear), and of course, Orion (the Hunter, probably my favourite).
I couldn't really understand why some of the asterisms (the shapes formed by groups of stars) were so named, though some of the stories behind them were imaginative to say the least, most being based on ancient mythology.
Even now I have a mental block with accepting most of them, they seem so obscure and I can understand how people fresh to this hobby might have difficulties recognising any but the most obvious. That said, throughout the centuries they've come to be accepted, indeed revered by many civilisations and I can't think of any other way of navigating around the heavens, so best learn them and maybe fantasise a bit as you stare up at them!

The human brain is actually well developed to register patterns and shapes so in practice, learning constellations should not be a great hardship, given some basic information. One such source of guidance is the monthly Sky At Night magazine. (Everyone's surely heard of the BBC TV programme, though I bet few could tell me when it actually goes out!)

Well, this magazine is edited by the great Patrick Moore and is great for all levels of astronomer - check it out, I don't think you'll be disappointed. In UK we have so few decent nights for viewing the heavens, you'll be able to spend the time profitably, indoors, learning about your hobby and planning your next celestial expedition!

The key thing is to enjoy what you're doing. And this is the International Year of Astronomy as you can see from the little banner on the right, so let's pray for some clear nights!

Seeing a planet for the first time, spotting meteors or maybe the Space Lab (perfectly possible if you know where to look, see here for information) brings a terrific sense of achievement. The higher up the ladder you climb (it would have to be a very long one, thinking about it!) brings you into contact with globular clusters, galaxies, nebulae and other fascinating deep-sky objects and before you know it, you're becoming an 'expert'.

Throughout the year there are lots of different objects to look at and there's always some new development in the field of astronomy which is being reported. Subscribe to the aforementioned magazine and read about what is coming in the next months.

I don't know about you but when I'm standing out there in the darkness, contemplating the meaning of life (42?) the main questions I seem to keep asking myself are, "So, how big is space?" and "Are we really alone?" (And "Oh dear, isn't it chilly!" sometimes....)

That's when your own imagination can take over, because nobody currently knows that any better than you. So put on some warm clothes (however dorky you think you might look, a hat is a must, really) and let's go spend some time staring into the heavens.

Planisphere

Showing sky at midnight on 5th July

One invaluable tool which I should mention, is what's called a Planisphere. It's a pair of overlaid circular plastic disks which rotate about a central pivot. The back one has a print of the heavens and around the periphery, dates for a whole year and sometimes, degrees. The top disk is mostly opaque but has a transparent oval window. Around the periphery of this are the times of the day by hourly segments, normally. A planisphere is designed for whatever hemisphere and lattitude you live in, but as long as you buy locally, you'll get the right one.

Dependent on what time you set against what date, you will see the appropriate sky-scene in the window. Hold this above your head (this is actually the trickiest bit!) with the east and west horizons orientated correctly, and you will get a good representation of what's up there. I would add that a small red torch is a godsend for this and any activities you want to enjoy outside in the dark.

Anyway, back to my experiences. I used to live on a housing estate Up North in Sunderland. Light pollution was an as-yet unheard-of swear-word and my eyes were a lot sharper then. We're talking over 35 years ago, by the way... Those were the days when you could pick out all the stars in the little bear, not so easy these days, sadly, and watch Comet Kohoutek from the front doorstep. I had a little refracting telescope which I used to look at the moon (don't underestimate the moon - it has so much to look at!). It wasn't very good. A toy, I would call it.

However, like all my hobbies and interests, what goes round, comes round and eight years ago my interest was reignited. I don't know what started it off but I recall buying my first 'scope in, ooh.... a long time (!) from Kingston, for nearly £200. It was a 115mm Bushnell reflector with a couple of eyepieces, on an Alt-Azimuth mount. and not a great one at that. In retrospect I probably paid too much for it. I still have it but the mirror needs re-aluminising - I'll get round to it one day.

Actually, that's not the whole story - My wife had just bought me a refractor for my birthday the previous month, through one of the dailies (a broadsheet which perhaps should have known better...) and quite frankly it was rubbish. The stand wasn't great and the draw tube wobbled when you touched it. It went straight back for refund with a letter of complaint/disappointment.

To clarify the above, there are two 'main' types of telescope, if you didn't know - the refractor and the reflector. There are also 'hybrids' of these systems, called catadioptrics, which are worth investigating if you have a little more cash but we'll pass over these for the moment.
Simply explained, the refractor is like your archetypal sailor's telescope where you look in one end and see what you're pointing at, magnified. However the reflector is a different animal, being a tube with a mirror at the bottom and the eyepiece sticking out of the side, near the top. A 'mini' refractor, if you like, sits on top of the tube for 'aiming' the main 'scope. That's called the 'finder' scope. You might find the reflector described as a 'Newtonian' since the eponymous Sir Isaac came up with the idea.

So this is the first bit of advice I can offer you:

If you want to buy a telescope (and many people will rightly tell you that a pair of decent binoculars will serve you equally well at the outset - you should be looking at something about 8x40 or 8x50) try to buy one from people who specialise in them. Reputable dealers won't sell you rubbish and will fall over themselves to give you expert advice whereas box-movers eg. Superstores, may not be able to do you justice where the appropriate equipment is required.

Been there, got the tee shirt, etc...

Getting it home, I immediately unpacked it and set it up in the back garden. Once again I lived on an estate, this time Down South, in Chessington, so I was prepared for a degree of light pollution from London to the north. It was dusk, the sky was clear and there was a bright object in the sky over to the east. OK, let's go...

So I aimed at it with the finderscope, which wasn't aligned (obviously, it having just been set up by myself out of the box) and saw nothing. Then I aimed it by lying on the ground and looking along the length of the main tube, up at this bright object (oh yes, I think we've all done it that way at some time!). Then I removed the eyepiece and aimed it by sighting the object in the reflection on the main mirror... Then after some perseverance and having replaced and focused the eyepiece, there it was, the target of my exertions in the centre of my view briefly but slipping slowly away as I watched.

Because the Earth is rotating a degree every 4 minutes or so, anything you are looking at through a fixed telescope will slide out of view at a rate dependent on the the magnification you are using. The higher the magnification (which gives you a narrower field of view), the faster your target will vanish! You can compensate for this by having a 'driven' mount, which exactly counteracts the earth's rotation.

Anyway, jiggling the tube on its mount, I managed to keep this thing pretty much central but was perplexed by what I was looking at. You know when you get reflections off camera lenses, maybe because you got the sun in the corner of the shot when you oughtn't have, and you see multiple bright spots in a line away from the main source? Well, this seemed to be what I was seeing. Remember, I was a newbie to this kit so I didn't know it wasn't faulty, somehow. After all, my previous experience with another telescope less than a month earlier, had been less than impressive...

So after checking the mirror and lenses for anything that might be causing this terrible aberration, I tried the other eyepiece (which gave me about three times the magnification of the first). Well, it all suddenly fell into place. The assumed aberration wasn't in the scope at all - it was actually about 700 million kilometres away.

What I'd actually been doing was looking at JUPITER and its four moons, Io, Europa, Ganymede and Callisto. WOW!!!! Forgive me for sounding excited but this was fantastic, a first for me. And as the night drew in and contrast improved, small as the image was, I could vaguely see stripes across the planet, though no red spot. OK, it's great to look at pictures of these things in a book or online, but being outside, seeing these things with your own eyes, is something else.

Next night and armed with a new copy of Patrick Moore's Yearbook of Astronomy 2003, I was out there again, hunting down quarry. In particular I wanted to find Saturn. Probably the most recognisable planet (next to ours!) I knew it was high to the south-west and it might look a bit yellower than the other points of light up there.....but not much bigger. Wait, let's get my specs on..... OK, that object up there looks possible, it's in the right sort of area according to the star charts....

And so it was with the finder scope zeroed-in on Jupiter earlier and with a bit of fiddling with the blessed mount, I got my first real-life view of arguably the most impressive planet in our solar system. It was a tiny image but I could plainly see the rings and the gap between the main ones. Sam came out for a look and was equally impressed.

"How far away? "
"A lot further than Jupiter"
"Wow.... We'll not be going there any time soon for holidays then, not if you won't sit on a plane for more than 3 hours."

So that was my inspiration to upgrade. I'd seen Saturn and I wanted more. I'd just learnt to drive and now wanted a racing car.

How can you do all the above in the dark?
Very few animals can see in the dark - some actually use infra-red, which is dark as we see it - but certainly humans can't! However, we can see in very low light if the conditions are right. Understanding how to achieve this is important (and simple) for you to get the best out of astronomy.

The eye recognises images with the retina which is in the back of your eye. It's composed of two types of light-sensitive cells - very sensitive rod cells which can only detect light/dark and all the shades of grey between, and cones which aren't quite as sensitive and recognise the colours. They all work together to bring you the image you see now.

The darker it gets, the less well the cones work, so you start to see in dull hues, then in shades of grey. As long as it gets progressively darker, chemicals in your body (rhodopsin, mainly, in association with Vitamin A) will help the rods to gather as much light as possible. There is of course a limit to how dark it is before you go 'blind', but you'll be amazed where that limit is!

But BEWARE!! As soon as your eyes catch a glimpse of white light (which is why going out when the moon is more than just a little crescent is a BAD thing...), your 'night vision' is destroyed and for a short period you'll be stumbling around like you have a bag over your head! However they will re-acclimatise to the darkness again, after about 15-30 minutes, depending on your age.

So how can you read maps and see what your doing on your telescope? Well, just like black-and-white photographic paper is, your eyes are very insensitive to RED light. This means that if you carry a little red torch with you, or a white one with red celluloid over the front, your dark vision will hardly be affected.

Upgrading the hardware
This is where I almost followed the 'right' course of action. Getting in touch with with advertisers in one of the astronomy monthly mags, I dropped into a specialist Telescope dealer near London's West End. There were actually two dealers in London at the time but one dealt mainly in the more 'professional' kit and it was a bit outside my league, so I opted to go 'cheap'. You live and learn...

I've only mentioned Refractors and reflector telescopes on Alt-Azimuth and Equatorial mounts thus far. Some come with computerised 'go-to' control which means that you barely need to actually recognise half a dozen key stars in the sky to be able to go observing quickly and easily. As prices fall these become more and more accessible to the novice. I think the minimum you should really go for in an equatorial mount, is a driven one. I personally see no place for a plain Alt-Az mount on modern telescopes.

This is where I can offer a second nugget of advice:

Don't necessarily buy biggest because it seems like you're getting more for your money, it doesn't always work that way. Buy quality, even if it's a bit smaller than you think you need - it pays off in the long run. Recommendations of other astronomers are always valuable so Google your local society and join it.

I'll do a review on my 'new' scope later to explain how you get what you pay for!

So, armed with blind enthusiasm and a piece of plastic with VISA stamped on it, I ordered a 10" (250mm) Newtonian reflector on a driven Equatorial stand. Then waited for it to be delivered.

A week or ten later, it arrived. Woo, Christmas again! I eagerly unwrapped and assembled it in the dining room so I could become familiar with it before committing to the garden. Anyway it was raining at the time so I was scuppered for viewing that night! Jeez, it was big.... There began a new learning process...

It was a couple of days before I could get out in the garden and use the 'scope in anger. In the meantime though, I'd read up on collimation, that black magic that you need to apply to ensure the image is sharp, and on polar alignment, not critical for normal observing but pretty important if you want to take pictures through the 'scope. You have to understand that a reflector is a bit more complicated than a refractor but the benefits are in bigger, brighter images through the eyepiece. Many refer to big reflecting telescopes as 'light buckets', for good reason.

So once everything was out there in the fresh air and stabilised (did I mention you have to leave these things for an hour or so before using them, to allow everything to aclimatise?) I was gobsmacked at what I could see. Everywhere I pointed it, stars.
Thousands and thousands.
Open clusters, globular clusters, double-stars... To be honest, I didn't know where to look next.

Saturn was still up there so once I'd located and centred it in my viewfinder (and with my tracking I could now keep it in field of view for ages). And because the image was brighter on account of the bigger mirror, I could use more magnification to look at it. It was beautiful.

A bone of contention among the astronomy fraternity is the emphasis some sellers put on the magnification a scope is capable of. It's invariably a theoretical maximum under ideal 'seeing' conditions, that you can seldom if ever achieve, so take it with a pinch of salt.

Magnification - the real numbers

To work out what magnification you are actually enjoying, there are some simple, basic numbers you need to understand; Magnification is defined by the focal length of the telescope divided by the focal length of the eyepiece you're using. All units of measurement have to be the same, millimetres in most cases. This information should be on a sticker somewhere on your 'scope.

To actually work out what the focal length is, it's the mirror (or object lens for refractors) diameter x focal ratio (given as anywhere between f4.0 and f8.0 typically.)

Thus my 'new' 250mm f4.8 reflector has a focal length of 250 x 4.8 = 1200 mm and will, using a 25mm eyepiece, give magnification 1200 / 25 = 48 times.

My 115mm f5.6 Bushnell has a focal length of 114.3 x 7.87 = 900. With the same 25mm eyepiece above, its magnification will be 36 times. You get the idea.

There is of course, another variable which greatly affects potential magnification and that's what's termed 'seeing'. Things might look great to the naked eye but as you know, the earth's atmosphere is full of dust and water vapour and even on a still night, will affect the quality of the image you can see. Looking straight up through 25 miles of atmosphere is bad enough but get down toward the horizon and you'll be looking through three or four times that much pollution! The tell-tale sign of bad atmosphere is seeing stars twinkling, so don't expect pin-sharp view at high magnification on these nights.

My 'new' 10" Newtonian reflector - over 5 years old!