Occultation - Occultation By Planets

Occultation By Planets

Stars may also be occulted by planets. In 1959, Venus occulted Regulus. Uranus's rings were first discovered when that planet occulted a star in 1977. On July 3, 1989, Saturn passed in front of the 5th magnitude star 28 Sagittarii. Pluto occulted stars in 1988, 2002, and 2006, allowing its tenuous atmosphere to be studied.

It is also possible for one planet to occult another planet. However, these mutual occultations of planets are extremely rare. The last such event occurred on January 3, 1818 and will next occur on November 22, 2065, in both cases involving the same two planets—Venus and Jupiter. Technically speaking, when the foreground planet is smaller in apparent size than the background planet, the event should be called a "mutual planetary transit". When the foreground planet is larger in apparent size than the background planet, the event should be called a "mutual planetary occultation". (See Transit for a list of past and future events).

Twice during the orbital cycles of Jupiter and Saturn, the equatorial (and satellite) planes of those planets are aligned with earth's orbital plane, resulting in a series of mutual occultations and eclipses between the moons of these giant planets. These orbital alignments have also occurred artificially when unmanned spacecraft have traversed these planetary systems, resulting in photographs such as the one shown here. The terms "eclipse," "occultation" and "transit" are also used to describe these events. A satellite of Jupiter (for example) may be eclipsed (i.e. made dimmer because it moves into Jupiter's shadow), occulted (i.e. hidden from view because Jupiter lies on our line of sight), or may transit (i.e. pass in front of) Jupiter's disk.

An occultation of Mars by Venus on 13 October 1590 was observed by the German astronomer Michael Maestlin at Heidelberg.