Wikipedia:Today's featured article/August 24, 2008

A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals. The planets were originally seen as a divine presence; as emissaries of the gods. As scientific knowledge advanced, the human perception of the planets changed over time, incorporating a number of disparate objects. On 24 August 2006, the IAU officially adopted a resolution defining planets within the Solar System. Copernicus suggested that the planets orbited the Sun, and this view was supported by Galileo after the development of the telescope. By careful analysis of the observation data, Johannes Kepler found their orbits to be not circular, but elliptical. Since 1992, through the discovery of hundreds of extrasolar planets, scientists are beginning to observe similar features throughout the Milky Way Galaxy. Planets are generally divided into two main types: large, low-density gas giants and smaller, rocky terrestrials. As of July 2008 there are 307 known extrasolar planets, ranging from the size of gas giants to that of terrestrial planets. This brings the total number of identified planets to 315. The Solar System also contains at least four dwarf planets: Ceres, Pluto, Makemake and Eris. No extrasolar dwarf planets have been detected. (more...)

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