Aug 24 2006
From The Space Library
The IAU revised its definition of the term “planet,” thereby stripping Pluto of its planetary status. The IAU, an organization of professional astronomers, establishes standards in the field of astronomy, such as definitions of astronomical constants and designations of celestial bodies. At a meeting in the Czech Republic, IAU members voted on a much publicized and debated resolution concerning the definitions of planets and other bodies in the solar system. The organization held the vote because new discoveries about celestial objects in the solar system had prompted debate among astronomers regarding the correct categorization of those objects. For example, astronomers had discovered that Pluto is far smaller than previous believed and has a more tilted orbit than the orbits of other planets. As a result of the vote, the IAU redefined the term “planet.” According to the new definition, a planet is a celestial body that orbits the Sun, is large enough for its gravity to give it a nearly round shape, and “has cleared the neighborhood around its orbit,” meaning that it has cleared other objects out of its orbital path and that its orbit does not cross the orbital paths of other objects. Because Pluto’s orbit overlaps with that of Neptune, the IAU reclassified Pluto as a “dwarf planet,” a new category of celestial object.
International Astronomical Union (IAU), “Resolution B5: Definition of a Planet in the Solar System,” http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf (accessed 28 February 2010); Dennis Overbye, “Vote Makes It Official: Pluto Isn’t What It Used To Be,” New York Times, 25 August 2006.
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