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Definition of planet. 1a(1) : any of the large bodies that revolve around the sun in the solar system. (2) : a similar body associated with another star.Is Pluto a planet or a planet?
In 2006, the International Astronomical Union developed a narrower definition of "planet," effectively demoting Pluto to the status of a "dwarf planet," a celestial body that is spherical and orbits the sun but is not large enough to disturb other objects from its orbit.How did the word planet originate?
The word "planet" originally described "wanderers" that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.Why did the IAU take so long to name planets?
Because new planets are discovered infrequently, the IAU did not have any machinery for their definition and naming. After the discovery of Sedna, it set up a 19-member committee in 2005, with the British astronomer Iwan Williams in the chair, to consider the definition of a planet.