Measurement

Measuring distances in astronomy is difficult but crucial. We need to know how far away objects are to look at the differences between them. Two objects can look different but be very similar, with one further away than the other. This can make them challenging to study.

Light is the main signal we receive from space. Almost everything we know about space has been found by measuring light.

One of the main ways to measure light is to look at the brightness. Measuring the brightness of something in space isn't as easy as you'd think though. 

Astronomers use angles a lot to work out where things are in the sky. We can measure the size of an object in the sky and mark its position by using angles.

If we know how much of the sky an object covers (as an angle) and how far away it is - we can work out its actual size.