On Planet Hunters we ask our volunteers to look for the signs of planets transiting in front of distant stars. By plotting the brightness of a star and seeing how it changes over time we get a graph called a ‘lightcurve’, and it’s shape allows us to determine the shape and size of any transiting object. In this festive video by Joe Llama, the object in question is not a planet at all!

Find tomorrow’s advent calendar treat at www.zooniverse.org/advent