Astronomical unit

The astronomical unit (AU or au or a.u. or sometimes ua) is a unit of distance, approximately equal to the mean distance between Earth and Sun. The currently accepted value of the AU is 149 597 870 691 ± 30 metres (about 150 million kilometres or 93 million miles).

Related Topics:
Distance - Mean - Earth - Sun

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The symbol "ua" is recommended by the Bureau International des Poids et Mesures http://www.bipm.org/en/si/si_brochure/chapter4/table7.html, but in the United States and other anglophone countries the reverse usage is more common. The International Astronomical Union recommends "au" http://www.iau.org/IAU/Activities/nomenclature/units.html and international standard ISO 31-1 uses "AU".

Related Topics:
Bureau International des Poids et Mesures - International Astronomical Union - International standard - ISO 31-1

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