The planets, including the Earth, all travel around the Sun in a continuous orbit. We can see them slowly make their way across the night sky. However, every now and then a planet appears to turn around and move back the way it came. This is called a retrograde orbit and is caused by the different speeds at which the planets circle the Sun. Academic content and direction: Martin Griffiths; Multimedia designer/developer: Barry Richards; Commentary texts: Toby Murcott; Voice-over artist: Chris Davies (drama student, Cardiff School of Creative & Cultural Industries, University of Glamorgan, 2010)