| Summary: | A planet (from Greek thavnins aothp "wandering star") is a celestial body orbiting a star or stellar remmant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals. The term planet is ancient, with ties to history, science, mythology, and religion. The planets were originally seen by many early cultures as divine, or as emissaries of the gods. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. In 2006, the International Astronomical Union officially adopted a resolution defining planets within the Solar System. This definition has been both praised and criticized, and remains disputed by some scientists. The planets were thought by Ptolemy to orbit the Earth in deferent and epicycle motions.
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