Greek astronomers employed the term asteres planetai for star-like objects which apparently moved over the sky. The issue of a clear definition for planet came to a head in January 2005 with the discovery of the trans-Neptunian object Eris. In August 2006, the International Astronomical Union released its decision on the matter during a meeting in Prague.
About Definition of planet in brief
The word planet dates back to ancient Greece. Greek astronomers employed the term asteres planetai for star-like objects which apparently moved over the sky. Over the millennia, the term has included a variety of different objects, from the Sun and the Moon to satellites and asteroids. The issue of a clear definition for planet came to a head in January 2005 with the discovery of the trans-Neptunian object Eris. In August 2006, the International Astronomical Union released its decision on the matter during a meeting in Prague. The IAU’s decision has not resolved all controversies, and while many astronomers have accepted it, some planetary scientists have rejected it outright, proposing a geophysical or similar definition instead. The definition, which applies only to the Solar System, states that a planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has ‘cleared its neighbourhood’ of smaller objects approaching its orbit. Under this formalized definition, Pluto and other trans-Nepunian objects do not qualify as planets. In his Natural History in 77 AD, Cicero’s Scipio proclaims, ‘Seven of these spheres contain the planets in each sphere, which move all to the contrary of the movement of heaven’ The single view of the seven planets is found in the Dream of ScIPio, written sometime around 53 BC, where the spirit of Scipios proclaims that the planets are so many that they shine with passing brightness in heaven.
In the 2nd century BC, Ptolemy refers to \”the Sun, Moon and five planets and five stars which many have called wandering, and which the Greeks have called the planets\” Manilius, a Latin writer, says, ‘Now the dodecory is divided into parts, so many are the stars called planets, which many are called the wanderers, which shine in heaven’ In the 4th century AD, the writer Marcus calls the planets ‘the wandering stars’ in his Astronomica, which is considered one of the principal texts for modern astrology. The word ‘planets’ is used to refer to a wide range of celestial bodies, from asteroids to comets to the Sun to the Moon, and even the Earth and the moon. The term ‘planet’ has been used by astronomers since the ancient Greeks to describe a range of astronomical bodies, including stars, planets, comets, and asteroids, as well as the solar system’s moons and comets. In modern astronomy, there are two primary conceptions of a ‘planet’, the orbital definition and the geophysical definition. The orbital definition states that an astronomical body moves like a planet, or whether it looks like a planets, and the Geophysical definition says that it has the appearance of a planet. The two definitions differ on technical details, such as whether a body orbits the sun or the moon, or if it has a large enough mass to be considered a planet in its own right.
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This page is based on the article Definition of planet published in Wikipedia (as of Dec. 06, 2020) and was automatically summarized using artificial intelligence.
