22: How To Measure The Universe

We've been so comfortable throwing around facts like "the Sun is 8 light seconds away" and "the nearest star is 4 light years away", it's easy to forget that measuring cosmic distances isn't as simple as pulling out a tape measure. So how *do* you measure how far it is to the moon, or the next star, or a distant galaxy? Emily gives us her top five rungs on the Cosmic Distance Ladder.