In this special programme, the Sky at Night takes to the air on board the largest airborne observatory in the world - a specially modified jumbo jet, flying out of California. This extraordinary aircraft is home to a 17-tonne telescope that observes the galaxy from around 40,000 feet. This telescope - called SOFIA - specialises in infrared astronomy. It can peer into the heart of a galaxy through the dust and gas, and see how stars form. It's designed to answer some of the biggest questions in astronomy: why aren't more stars being created and how do planets form?