Part 1 - What is a Telescope for ?

A big misconception of many an amateur astronomer, starting out, is that he or she must have a telescope. And to be seen without one at a star party just isn't on! This simply is not true.

Some of the best views to be had of the night sky have made use of that superior piece of apparatus, the mark one eye ball! Yes you can enjoy the night sky without any optical aid at all. And just because you are into astronomy does not mean you have to spend a fortune on a telescope.

I like to think of astronomy as an activity that evolves, starting with the mark one eye ball. After all no optical aid has such a wide field of view as the eye, that's why you can't use a telescope to view a meteor shower, for example. You sometimes need that really wide field of view. I will explain field of view later on.

But where the eye fails is in the collection of faint light. If we take a modest pair of binoculars, for instance, they might have an aperture (size of the lenses at the front) of say 50mm. Your eye may only have an aperture of about 5mm. This is determined by the size of the pupil once your eyes have grown accustomed to the dark. Let me take you back to those boring maths lessons. Because we have increased the aperture, from 5mm to 50 we have increased the light gathering power as well, you might think by something like 10 times? In actual fact its much more than that. Now the maths.

The area of a circle is proportional to the square of the radius multiplied by Pi

So this means the area of your eye is 19.6 square mm. Now compare that with the area of the binocular lens, which has an area of 1962 square mm, which is about 100 times more area! This effectively means almost 100 times more light gathering power from the binoculars. Quite a difference!

Dont confuse light gathering power with magnification, I will come to that later.

The light gathering power is a measure of much of that valuable light, that has travelled so far across space, is collected. The more light collected the fainter the objects we can see and the further back in time we can see. How mind blowing is that?

So you can begin to see why, as an astronomer you might want to use an optical aid. And since I mention binoculars, this is an excellent bit of kit to start with. Binoculars, especially those that can be mounted on a tripod, offer great wide field views of the night sky. The Milky Way, our galaxy, is an awe inspiring view through binoculars on a warm summers evening. Plus the added bonus that they can be used during the day too.

How do binoculars work then? If you think of binoculars as being two telescopes strapped together, one for each eye, this is basically what they are. In fact binoculars work along the same lines as the first type of telescope I want to talk about here. Please read on and all will become clear!