An astronomical unit (abbreviated as AU, au, a.u., or ua) is a unit of length equal to 149,597,870.700 kilometres (92,955,807.2730 mi) or approximately the mean Earth–Sun distance.
The symbol ua is recommended by the International Bureau of Weights and Measures, and the international standard ISO 80000, while au is recommended by the International Astronomical Union, and is more common in Anglosphere countries. In general, the International Syste...
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An astronomical unit (abbreviated as AU, au, a.u., or ua) is a unit of length equal to 149,597,870.700 kilometres (92,955,807.2730 mi) or approximately the mean Earth–Sun distance.
The symbol ua is recommended by the International Bureau of Weights and Measures, and the international standard ISO 80000, while au is recommended by the International Astronomical Union, and is more common in Anglosphere countries. In general, the International System of Units only uses capital letters for the symbols of units which are named after individual scientists, while au or a.u. can also mean atomic unit or even arbitrary unit. However, the use of AU to refer to the astronomical unit is widespread. The astronomical constant whose value is one astronomical unit is referred to as unit distance and is given the symbol A.
The AU was originally defined as the length of the semi-major axis of the Earth's elliptical orbit around the Sun. In 1976 the International Astronomical Union revised the...
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