Solar eclipses on Jupiter
|This article needs additional citations for verification. (September 2014)|
Solar eclipses on Jupiter occur when any of the natural satellites of Jupiter pass in front of the Sun as seen from the planet Jupiter. For bodies which appear smaller in angular diameter than the Sun, the proper term would be a transit. For bodies which are larger than the apparent size of the Sun, the proper term would be an occultation.
There are 5 satellites capable of completely occulting the Sun: Amalthea, Io, Europa, Ganymede and Callisto. All of the others are too small or too distant to be able to completely occult the Sun, so can only transit the Sun. Most of the more distant satellites also have orbits that are strongly inclined to the plane of Jupiter's orbit, and would rarely be seen to transit.
Eclipses of the Sun from Jupiter are not particularly rare, since Jupiter is very large and its axial tilt (which is related to the plane of the orbits of its satellites) is relatively small—indeed, the vast majority of the orbits of all 5 of the objects capable of occulting the Sun will result in a solar occultation visible from somewhere on Jupiter's surface.
The related phenomenon of satellite eclipses in the shadow of Jupiter has been observed since the time of Giovanni Cassini and Ole Rømer in the mid Seventeenth Century. It was soon noticed that predicted times differed from observed times in a regular way, varying from up to ten minutes early to up to ten minutes late. Rømer used these errors to make the first accurate determination of the speed of light, correctly realizing that the variations were caused by the varying distance between Earth and Jupiter as the two planets moved in their orbits around the Sun.
Spacecraft can be used to observe the solar eclipses on Jupiter, these include Pioneer 10 and Pioneer 11 (1973 and 1974), Voyager 1 and Voyager 2 (1979), Galileo orbiter (1995–2003), Cassini–Huygens (2000) and New Horizons (2007) observed the transits of their moons and its shadows.
Visibility from Jupiter
The mean apparent size of the Sun from is 372 arcseconds, varying slightly from 381" to 357" between perihelion and aphelion. Unlike the near-coincidence of lunar and solar apparent diameters on Earth, the Galilean satellites all appear much larger than the Sun; even distant Callisto is over 50 percent larger, and Io is nearly six times larger. This disparity in angular size makes the moons' shadows sharper and more well-defined on Jupiter than the lunar shadow on Earth during total solar eclipses, as it narrows the penumbra for a given distance.
- SkyTonight – predictions for eclipses of Jovian moons and their shadow transits