Since people first gazed up at the night sky, we have been asking ourselves what is up there. Today we know that billions of planets orbit billions of stars in the universe. But without being able to see them, how can we be so sure? Follow our guide to the vastness of the galaxy.

Swiss scientists Michel Mayor and Didier Queloz were the first to discover a planet outside our solar system back in 1995. Since then, the catalogue of planets orbiting stars other than the sun (exoplanets) has grown week by week. Although the first photos are now emerging, worlds trillions of kilometres away are still being discovered by indirect methods. This animated film explains those methods. (swissinfo.ch)