The planets were thought by Ptolemy to orbit Earth in deferent and epicycle motions. Although eight of the planetary bodies discovered before 1950 remain 'planets' under the current definition, some celestial bodies, such as Ceres, Pallas, Juno and Vesta (each an object in the solar asteroid belt), and Pluto (the first trans-Neptunian object discovered), that were once considered planets by the scientific community, are no longer viewed as planets under the current definition of planet. This definition is controversial because it excludes many objects of planetary mass based on where or what they orbit. In 2006, the International Astronomical Union (IAU) officially adopted a resolution defining planets within the Solar System. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. These were regarded by many early cultures as divine, or as emissaries of deities. Apart from Earth itself, five planets in the Solar System are often visible to the naked eye.

The term planet is ancient, with ties to history, astrology, science, mythology, and religion. Sizes are not to scale.Ī planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and – according to the International Astronomical Union but not all planetary scientists – has cleared its neighbouring region of planetesimals.

Shown in order from the Sun and in true color. Jupiter and Saturn ( gas giants) Uranus and Neptune ( ice giants) The eight known planets of the Solar System: Class of astronomical body directly orbiting a star or stellar remnant

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