Many people may wonder how on Earth we are able to measure how far away an object in space, such as a star, actually is. Obviously we can't use any kind of regular tape measure, and we can't use anything modern like a laser - even if you could shine one all the way to a star you would have to wait hundreds, or thousands of years just for the light to get there!

Scientist measure the distance to stars using an optical effect called Parallax. It's actually quite easy to demonstrate how this works - hold up a finger or a pen close to your face, just close enough not to cross your eyes, and look at the tip while you move your head from side to side - it appears to move relative to the objects in the background. Now do the same thing while holding your finger or pen at arm's length, you should notice that the tip seems to move less than the first time - this is parallax.

The same method is applied to stars by observing their shifting positions at different points in the Earth's orbit around the Sun. For stars that a very long way away, scientist can also make a good estimate of  their intrinsic brightness and compare this with their observed brightness in the sky to make distance measurments.