An astronomical unit (abbreviated as AU, au, a.u., or sometimes ua) is a unit of length equal to about 149,597,871 kilometres (92,960,000 miles). It is defined by the International Astronomical Union, and is defined as the mean distance between the Earth and the Sun over one Earth orbit. The symbol au is recommended by the International Bureau of Weights and Measures, but au is more common in Anglosphere countries. The International Astronomical Union recommends au, while international standard ISO 31-1 uses AU. In general, capital letters are only used 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 given the symbol A.

Данное издание не является оригинальным. Книга печатается по технологии принт-он-деманд после получения заказа.