Fifth planet (hypothetical) Fifth planet (hypothetical) In the history of astronomy, a handful of Solar System bodies have been counted as the fifth planet from the Sun. Under the present definition of a planet, Jupiter is counted as the fifth. There are three main ideas regarding hypothetical planets between Mars and Jupiter. During the early 19th century, as asteroids were discovered, they were considered planets. Jupiter became the sixth planet with the discovery of Ceres in 1801. Soon, three more asteroids, Pallas (1802), Juno (1804), and Vesta (1807) were discovered. They were counted as separate planets, despite the fact that they shared an
Solar eclipses on Jupiter to 357" at aphelion. Unlike the near coincidence of the apparent sizes of the Moon and Sun as viewed from Earth, this perspective exaggerates the apparent diameters of all the Galilean moons in comparison to the Sun. Even distant Callisto is over 50% larger, and Io is nearly six times as large. This disparity in angular size makes the moons' shadows on Jupiter more defined than the lunar shadow on Earth during a total solar eclipse, as it narrows the penumbra for a given distance. Solar eclipses on Jupiter Solar eclipses on Jupiter occur when any of the natural satellites