| Astrophysics (Index) | About |
An occultation occurs when one celestial body hides another, i.e., it enters an observer's line of sight and is large enough that the further body is not visible. In contrast, a transit is one body hiding part of another by passing in front of it, and an eclipse is one body throwing a shadow on another, e.g., when two planets are in a line with their star. Occlusion refers to a visible obstruction, including the effects of a somewhat transparent object such as a cloud, e.g., the phrase partial occlusion. These terms are not mutually exclusive: often they describe different aspects of the same scenario.
Occultations are useful to astronomy, e.g., detection of extra-solar planets (transit method). Atmospheres of both exoplanets and solar system bodies are studied using occultation, by studying the spectra absorbed by the body's atmosphere when that atmosphere is in front of another body producing EMR (transmission spectroscopy). Spectra can also be studied using the differences produced by an occultation (differential spectroscopy). Occultations also can offer precise astrometric data, e.g., if precise data is already known regarding one of the bodies. They can also be used to determine the size of bodies.