Brian Cox and Dara O Briain raise the stakes in the final night of their astronomy extravaganza, and reveal the results of their viewers' challenge to find undiscovered galaxies at the edge of space. Reporting live from above the clouds in Norway, Liz Bonnin has one last chance to capture the spectacular Northern Lights, using super-sensitive cameras. Brian reveals why no-one really knows what our own galaxy, the Milky Way, really looks like, and how the remarkable Gaia space probe is set to change all that by mapping a billion of our neighbouring stars. With his sights set on a weekend break to a distant planet, Dara prepares to suffer as he straps himself into a human centrifuge to find out whether humans can accelerate to light speed. Meanwhile, resident astronomer Mark Thompson joins thousands of amateur astronomers at one of the spectacular stargazing parties taking place across the country, and looks ahead at the treats the night sky has in store over the year.