Occultation over observatories. Venus (small bright body) about to disappear behind a crescent moon over astronomical observatories at Mauna Kea, Hawaii. An occultation occurs when one celestial body disappears behind another. This one was photographed on 1 April 1993 and combined with a photograph of telescope domes to make a composite image. Mauna Kea is a dormant volcano. Its clear skies and high altitude make it one of the world's best sites for astronomical observations.