Astronomical unit

Astronomical unit
Astronomical unit.png
The grey line indicates the Earth–Sun distance, which on average is about 1 astronomical unit.
General information
Unit systemAstronomical system of units
(Accepted for use with the SI)
Unit oflength
Symbolau, ua, or AU 
1 au, ua, or AU in ...... is equal to ...
   metric (SI) units   149597870700 m
   imperial & US units   9.2956×107 mi
   astronomical units   4.8481×10−6 pc
   1.5813×10−5 ly

The astronomical unit (symbol: au,[1][2][3] ua,[4] or AU) is a unit of length, roughly the distance from Earth to the Sun and equal to about 150 million kilometres (93 million miles). However, that distance varies as Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once a year. Originally conceived as the average of Earth's aphelion and perihelion, since 2012 it has been defined as exactly 1.495978707×1011 m.[5] The astronomical unit is used primarily for measuring distances within the Solar System or around other stars. It is also a fundamental component in the definition of another unit of astronomical length, the parsec[6].

History of symbol usage

A variety of unit symbols and abbreviations have been in use for the astronomical unit. In a 1976 resolution, the International Astronomical Union (IAU) had used the symbol A to denote a length equal to the astronomical unit.[7] In the astronomical literature, the symbol AU was (and remains) common. In 2006, the International Bureau of Weights and Measures (BIPM) had recommended ua as the symbol for the unit.[8] In the non-normative Annex C to ISO 80000-3 (2006), the symbol of the astronomical unit is "ua".

In 2012, the IAU, noting "that various symbols are presently in use for the astronomical unit", recommended the use of the symbol "au",[1] as did the American Astronomical Society (AAS) in the manuscript preparation guidelines for its principal journals.[3] In the 2014 revision and 2019 edition of the SI Brochure, the BIPM used the unit symbol "au".[9][10]

Other Languages
العربية: وحدة فلكية
azərbaycanca: Astronomik vahid
Bân-lâm-gú: Thian-bûn tan-ūi
беларуская (тарашкевіца)‎: Астранамічная адзінка
Cymraeg: Uned seryddol
Esperanto: Astronomia unuo
한국어: 천문단위
Bahasa Indonesia: Satuan astronomi
ಕನ್ನಡ: ಖಗೋಳ ಮಾನ
Kiswahili: Kizio astronomia
Lëtzebuergesch: Astronomesch Eenheet
Lingua Franca Nova: Unia astronomial
Bahasa Melayu: Unit astronomi
မြန်မာဘာသာ: Astronomical unit
日本語: 天文単位
norsk nynorsk: Astronomisk eining
oʻzbekcha/ўзбекча: Astronomik birlik
ਪੰਜਾਬੀ: ਖਗੋਲੀ ਇਕਾਈ
پنجابی: اسمانی میل
Piemontèis: Unità Astronòmica
Plattdüütsch: Astronoomsch Eenheit
Simple English: Astronomical unit
slovenščina: Astronomska enota
Soomaaliga: Astronomical unit
srpskohrvatski / српскохрватски: Astronomska jedinica
татарча/tatarça: Астрономик берәмлек
Tiếng Việt: Đơn vị thiên văn
吴语: 天文单位
粵語: 天文單位
中文: 天文單位