This episode aimes to explain how it's possible to chart the history of the universe by looking million of light years out into the depths of space.
Meanwhile, Mark Thompson reveals what can be learned from the colours of the stars.
At NASA, Liz Bonnin meets the team building the largest space telescope in the world, an instrument that's 100 times more powerful than the Hubble.
Visit our Stargazing LIVE hub to order a free Star Guide, watch animated videos, play with planetary interactives and more. See our Universe-related content below...