Notes from Around the Sundial

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Gnomon's column image, showing a sundial surrounded with the words Notes From Around the Sundial'

I've been writing for h2g2 for years—I'm rather well known for it, having written many Entries which made it into the Edited Guide. I also try to keep a fairly regular journal which outlines the exciting or mundane events of my life for all to see. Up until now, I've kept away from The Post. Recently I found that I'm not in the mood for writing Edited Entries at the moment, so, with a little persuasion, I've been encouraged to write something for this illustrious journal. It shouldn't be too difficult to produce about a thousand words a fortnight, and I'll get a shiny new badge to add to my collection. (I'm not really a badge collector, as people may know, so this is not a big attraction for me).

I've decided to call this column 'Notes from Around the Sundial' for reasons which I'll explain later on. I've a wide range of interests, so I hope that there'll be something for everyone here. But don't expect anything about football.

My New Telescope

I'll start by talking about my new telescope, which was delivered last week. I've always loved looking at the stars, but living in a city, I don't see them very often, as light from all the street lamps reflects off the sky and dims the stars. I've a mobile home in the countryside where we often go for weekends, and the stars are much clearer there, so I finally decided I should invest in a decent telescope.

I've seen telescopes on sale in camera shops, but the salesmen generally know very little about them. It's best to buy a telescope from a specialist. I got mine from the Astronomy Ireland website.

Telescopes can be confusing if you haven't studied them. Most people think their main purpose is to make far-away things closer, but for astronomical telescopes this is not strictly true. The stars are so far away that they appear as points of light. If you magnify them a few hundred times, they still appear as points of light, so they don't look any different. The real purpose of the telescope is to gather light. This enables you to see things that are much dimmer than you can see with your naked eye. Many of the sights in the sky are actually big enough to see but are far too dim - the Andromeda Galaxy, for example, would be seven times as wide as the full moon, but it is so faint that we can only barely see the central bulge of it. Telescopes do enlarge things a bit as well, but not as much as many people think.

My telescope is a refractor, which means that it uses a giant lens as the main light-gathering device (some telescopes use curved mirrors). The big lens is at one end of a tube and there's a small lens at the other end, the end you look into. There's a little mirror at the small end which turns the view through 90° so you don't have to lie on your back and look upwards to see the stars. The big lens is 102mm across, which sounds very metric until you realise that it is four inches. The telescope was designed in America, one of the few places in the world that still uses British Imperial Units. This big lens can gather more than 200 times as much light as the human eye, so I should be able to see plenty.

The small lens is in a removable part, called an eyepiece. You can buy different eyepieces, which provide different magnifications. This one came with two eyepieces, which provide 25X and 75X magnifications. I could pay extra for anything down to about 15X (for bright views of wide star fields) or up to about 200X (for looking at things like the rings of Saturn). I'll have to consider this - having whacked out a few hundred Euros for the telescope, the first thing I was confronted with was an offer of some good eyepieces for only €200! I can see that this hobby could become expensive.


In the old days, there were two ways of mounting the telescope on the tripod. The cheap way is called 'altazimuth', an elaborate name for a simple system. The telescope can turn around a vertical axis, and it can also independently be tilted up and down. The problem with this is that the stars move across the sky as the earth rotates. At higher magnifications they appear to go quite quickly, and they move in diagonal lines, so you have to adjust the horizontal and vertical positions of the telescope simultaneously to track the star. More expensive telescopes have an equatorial mount, which means that the main axis around which the telescope turns is parallel to the axis of the earth so the stars can be tracked easily.

With modern telescopes, including my one, the position of the telescope is determined by computer-controlled motors, so this is not really an issue. You just tell the telescope to track the star and it can automatically follow it. This involves a little setting up, but it gives the bonus that you can select any star, planet, nebula or galaxy from a list on the controller and it will turn the telescope to point to it.

The procedure for setting up the telescope sounds very simple. All you have to do is point it at three bright stars and press a button after each one. You don't even have to know what stars they are; the built-in computer will figure that out. Sadly, last night there were only two stars visible.

So now all I need is a clear night so that can I try out my new instrument. I'll let you know how I get on in subsequent articles in The Post, but don't worry, this column won't all be about astronomy. I'll have plenty of down-to-earth stuff as well.

Notes from Around the Sundial Archive


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