occultation

An occultation is an astronomical event in which one object in the foreground passes in front of another object, blocking its light or signal from an observer. The event occurs when the relative positions and motions of the bodies align so that the foreground object obscures or dims the background object.

Stellar occultations occur when a foreground body such as the Moon, a planet, or a minor planet passes between an observer and a distant star, causing the star to vanish and reappear. Lunar occultations are common for observers on Earth and have historically provided measurements of stellar angular diameters and precise timings for refining lunar and orbital models. Planetary occultations, though rarer, can yield information about the planet’s silhouette and, in some cases, its atmosphere or ring system when a star’s light is filtered during the event.

Solar occultations happen when a body occludes the Sun from a given vantage point; the most familiar instance is a solar eclipse, where the Moon blocks the Sun as seen from Earth. Occultations by planets or the Moon of background stars also help improve astrometric positions and refine ephemerides, while mutual occultations in binary star systems can reveal orbital and physical properties of the pair.

In radio and space science, occultation methods extend beyond visible light. Radio occultation uses the occultation of signals from spacecraft or quasars by planetary atmospheres or the Earth’s atmosphere to derive temperature, pressure, and composition profiles, contributing to atmospheric science and geodesy.