Science Explained: What is a light year?

Distances in space are enormous - so big that our standard units of measurement, kilometres and miles, are just too small to be useful.

So scientists use something else - the light year.

But what is it and how does it work?

Dr Tim O'Brien from the Jodrell Bank Centre for Astrophysics at the University of Manchester explains.

Please note: The graphics used in this video are not to scale

Images courtesy of Nasa