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Several thousands of planets around other stars ("extrasolar planets" or "exoplanets") have been discovered in the Milky Way.
As of 1 September 2019, 4,109 known extrasolar planets in 3,059 planetary systems (including 667 multiple planetary systems), ranging in size from just above the size of the Moon to gas giants about twice as large as Jupiter have been discovered, out of which more than 100 planets are the same size as Earth, nine of which are at the same relative distance from their star as Earth from the Sun, i.e. The idea of planets has evolved over its history, from the divine lights of antiquity to the earthly objects of the scientific age.
Five planets in the Solar System are visible to the naked eye.
These were regarded by many early cultures as divine, or as emissaries of deities.
The ancient Greeks initially did not attach as much significance to the planets as the Babylonians.
Planets are generally divided into two main types: large low-density giant planets, and smaller rocky terrestrials. In order of increasing distance from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four giant planets, Jupiter, Saturn, Uranus, and Neptune.
Six of the planets are orbited by one or more natural satellites.
In the 3rd century BC, Aristarchus of Samos proposed a heliocentric system, according to which Earth and the planets revolved around the Sun.
The geocentric system remained dominant until the Scientific Revolution.