An occultation is whenever one object in the sky passes in front of another and temporarily obscures our view of that second object. As enormous as space is, different objects do still sometimes line up and when this happens we say that the nearer object has “occulted” the further one. Most occultations are caused by the Moon – it’s quite large and moves quite fast against the stellar background, so it occults any number of stars every day. Less often, it will occult one of the planets, and that’s something amateur astronomers make a special effort to see. Solar Eclipses are a special case of occultation, when the Moon occults the Sun. Sometimes inner planets occult the Sun, but this is rare enough that you can go decades between events. Rarest of all are tiny distant objects like asteroids and dwarf planets occulting stars – the alignment has to be absolutely perfect, and they are very hard to predict. “Occult”, incidentally, comes from the latin word occultō (meaning “hide”, or “keep secret”), which is why magical or spiritual concepts are often categorised as “The Occult”. The astronomical use of the word has no connection!
Written by Allen Versfeld