Standard Candles

Standard candles are used to
calculate relative distances.
Credit: Wikimedia (user Bangin)

Imagine that you have a type of star that is easy to recognise and is always exactly the same. In other words, if you were to put two of these stars side-by-side, it would be very hard to tell them apart.

Light Year

Distance from Earth to, Proxima Centauri (not to scale)
Credit: Mandy Bailey and Wikimedia
The light-year is a way of measuring distance - and not time as you might think from the name.

It is the distance that light travels in one year.