Notes from Around the Sundial
Created | Updated Jul 30, 2008
First Experiences of a Telescope User
I told you a few weeks ago that I had just bought a new telescope. This is the first proper astronomical telescope I've ever owned so I'm a beginner at all things astronomical. Well, I've had a chance to try out the telescope and I thought I'd better report on it. I'm going to state a few rules. These are things I've discovered for myself, but I'm not claiming any great originality here. They're well known to anyone who uses a telescope regularly.
Gnomon's First Rule: There's always a bigger telescope.
You've bought a 100mm telescope and paid several weeks' or months' wages for it, and then you see magazines advertising 1000mm telescopes. Your telescope is heavy enough that you can only barely lift it, but the monsters in the magazines weigh half a ton. Yours can see the disc of Jupiter, but there's an amateur in Montana who can take photos of not just the Red Spot and the Red Spot Junior, but also the Little Red Spot. However much you can afford, there'll always be a bigger, better telescope that you can't afford. So prepare yourself right from the start to be happy with what you've got. This is very important.
OK. With that out of the way, let's get down to talking about what you can and can't see with a telescope. The next rule, which I mentioned in the other column, is that big magnification is not necessarily what you're looking for. It depends on what you're looking at. Stars are so far away that they appear as points of light. Magnify them 200 times and they will still look like points. Planets, on the other hand, look like very tiny discs, so if you magnify them, you'll see larger discs and with a bit of luck you might see some surface markings as well.
Gnomon's Second Rule: Use High or Low Magnification as appropriate.
So what sort of things might you want to see?
A planet: you'll need very high magnification. The best you'll be able to achieve is twice the diameter of the front lens of your telescope when measured in millimetres. My telescope has a 100mm front lens so it will magnify up to about 200 times. This is good enough to clearly see the discs of the major planets. I have yet to see any markings on them, but Saturn is a sight to behold with its rings, and Jupiter's four moons are good to see too. You can nearly always see three of the four, and occasionally all four, as four little dots in a line around the planet. Venus has no surface markings, but at certain times of the year (when it is brightest) it is a crescent, like a tiny moon. This comes as a surprise to many people.
A loose cluster of stars: these will require low magnification. Too much magnification and you'll see only a portion of the group. With a magnification of 15X, you'll get a beautiful bright image from your telescope. Good candidates, depending on the time of year, are the Beehive Cluster (M44) in Cancer or the Pleiades (M45) in Taurus. Both of these groups are spectacular through a telescope.
A globular cluster: these groups of stars are much more tightly bound together. Whereas a loose cluster might have 10 or 20 stars, a globular cluster may have 100,000. They're very compact and very far away, so you'll need high magnification. M13 in Hercules is probably the best one.
Binary stars: many of the lights in the sky that look like single stars are actually double stars orbiting around each other: either a big and a small, with the small one going around the big, or two equally sized stars swinging around each other like ballroom dancers. Usually a medium magnification is best for looking at these. The two components may be the same colour, as in epsilon Lyrae, or may be totally different colours, as in Albireo (beta Cygni). This latter is particularly beautiful.
Galaxies: some galaxies are actually very big as seen from Earth - the closest full-sized galaxy to us is the Andromeda Galaxy (M31) and it is about seven times the size of the full moon. The reason we don't see it taking up a large part of the sky is because it is so faint. So the lowest magnification possible is needed which will also gather the maximum amount of light. Other galaxies can be very spectacular, and you'll see plenty of photos of them in the magazines, but you won't be able to see much detail in them without a very big telescope.
Nebulas: (or if you're pedantic, nebulae). These are clouds of glowing dust. Planetary nebulas aren't anything to do with planets - they're called that because they are basically circular in shape and are sometimes mistaken for planets. They're actually shells of gas and dust thrown off by giant stars which are nearing the end of their lives. A good example is the Ring Nebula M57 in Lyra. This will need a good high magnification. At 75x it is only barely discernable as a ring. On the other hand, at 150x, you'll need a very good clear dark night and good night vision to be able to see it, as it will be very faint. The other sort of nebula is the diffuse nebula which is an irregular cloud of dust and gas - there's a good one in Orion (M42) and another good one in Carina (NGC 3372) - particularly good if you're in the Southern Hemisphere).
The Moon: the moon is good at any magnification, and since it is very bright, you'll have no problem looking at it at very high magnifications which are the most interesting. Full moon is not the best time, as all the features are the same brightness and hard to make out as a result. With a crescent or half moon, you'll see shadows which pick out the mountains and craters.
Well, those are the main things you're going to be hunting for with your telescope. I've had some success with some of these. Almost as soon as I got the telescope, someone asked me for a photograph of the stars. This leads me to my third rule:
Gnomon's Third Rule: Be content to look, don't try to photograph.
The equipment needed to photograph the stars is much more expensive than the simple stuff you need just to look and be amazed. Your image may be sharply in focus at the centre and slightly out of focus at the edges, which won't worry you when you look but will look bad on a photo. A more expensive type of 'scope is needed to make it clear all the way across. Secondly, it's all extremely faint so your camera may need a long exposure, and the stars will have moved during this time, so you'll need a high quality tracking motor which exactly tracks the stars. The list goes on and on. When you've a year or two of star gazing done and you understand all the technicalities, then you can start really spending money and photographing the stars.
Gnomon's Fourth Rule: Memorise the constellations and the names and reference numbers of the stars and main sights you're going to look for.
When you're out in the dark, you want your eyes to become adjusted to the dark so that you can see the best possible images. If you've a computerised mount on your telescope, as most of them do these days, you can type in M13 and it will point the telescope to the Great Globular Cluster in Hercules. The last thing you want is to have forgotten the number of the cluster and to have to turn on a torch to read your books and look it up, ruining your night vision.
I think that's enough rules for the moment. I'll report back in a couple of months with some more advice on telescopes and the night sky.
