Contributions of 'citizen science' to occultation astronomy.

The modern term 'citizen science' describes a very old tradition in the natural sciences. Until the specialization of the sciences at the end of the eighteenth century, the emergence of technical universities and the formation of a modern scientific enterprise, citizen science was the norm. Since the 1960s, amateur astronomers have increasingly observed stellar occultations, first by the Moon and in the last three decades by main belt asteroids and outer solar system bodies. As in other branches of astronomy, occultation work has profited tremendously from technological advances in the last 40 years. Special for occultation work citizen scientists have developed cameras with millisecond-precise absolute timing that is necessary in occultation work. Modern star catalogues, such as the Hipparcos, UCAC and, lately, the Gaia catalogues, have helped to improve predictions of such events. Easy to handle software to predict occultations has been developed for the occultation observers. Cooperations and networks between professionals and amateurs have led to scientific improvement and coverage of occultations. This results in many peer-reviewed publications, where amateurs play an increasing role.This article is part of the theme issue 'Major advances in planetary sciences thanks to stellar occultations'.