It is not just our sun that is circled by planets. In recent years, astronomers have found over 4,000 planets circling stars other than our own. The Sky at Night team investigates what we know about these alien worlds and looks at how we have managed to detect them.Professor Chris Lintott visits the UK Astronomy Technology Centre in Edinburgh to see a cutting-edge camera designed to take pictures of exoplanets. And Dr Maggie Aderin-Pocock talks to experts about the continuing hunt for alien worlds and, even, alien moons.Meanwhile, Pete Lawrence sticks to hunting for planets in our own backyard, looking for Neptune and explaining what is meant when a planet is said to be in opposition.