This video segment adapted from Shedding Light on Science describes how astronomical distances can be measured in units of light-years, and how the finite speed of light allows astronomers to study how the universe looked long ago....

So you know what a star is, right? Well, if you don't, you should. We've talked about that big one in the sky a few times: The Sun! But there are a lot of bright dots in the night sky and not all of them are stars. Today, let's play a...