This article is about the unit of length. For constants, see astronomical constant. For units in astronomy, see astronomical system of units. For other uses of "AU", see Au.
Astronomical unit
The grey line indicates the Earth–Sun distance, which on average is about 1 astronomical unit.
General information
Unit system
Astronomical system of units (Accepted for use with the SI)
Unit of
length
Symbol
au or AU or AU
Conversions
1 au or AU or AU in ...
... is equal to ...
metric (SI) units
1.495978707×1011 m
imperial & US units
9.2956×107 mi
astronomical units
4.8481×10−6 pc 1.5813×10−5 ly 215.03 R☉
The astronomical unit (symbol: au,[1][2][3][4] or AU) is a unit of length defined to be exactly equal to 149,597,870,700 m.[5] Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its modern redefinition in 2012.
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] One au is equivalent to 499 light-seconds to within 10 parts per million.
^On the re-definition of the astronomical unit of length(PDF). XXVIII General Assembly of International Astronomical Union. Beijing, China: International Astronomical Union. 31 August 2012. Resolution B2. ... recommends ... 5. that the unique symbol "au" be used for the astronomical unit.
^"Monthly Notices of the Royal Astronomical Society: Instructions for Authors". Oxford Journals. Archived from the original on 22 October 2012. Retrieved 20 March 2015. The units of length/distance are Å, nm, μm, mm, cm, m, km, au, light-year, pc.
^Cite error: The named reference AAS_style was invoked but never defined (see the help page).
^Le Système international d’unités [The International System of Units] (PDF) (in French and English) (9th ed.), International Bureau of Weights and Measures, 2019, p. 145, ISBN 978-92-822-2272-0
^On the re-definition of the astronomical unit of length(PDF). XXVIII General Assembly of International Astronomical Union. Beijing: International Astronomical Union. 31 August 2012. Resolution B2. ... recommends [adopted] that the astronomical unit be re-defined to be a conventional unit of length equal to exactly 149,597,870,700 metres, in agreement with the value adopted in IAU 2009 Resolution B2
^Luque, B.; Ballesteros, F.J. (2019). "Title: To the Sun and beyond". Nature Physics. 15: 1302. doi:10.1038/s41567-019-0685-3.
The astronomicalunit (symbol: au, or AU) is a unit of length defined to be exactly equal to 149,597,870,700 m. Historically, the astronomicalunit was...
The astronomical system of units, formerly called the IAU (1976) System of Astronomical Constants, is a system of measurement developed for use in astronomy...
"Resolution B2 on the re-definition of the astronomicalunit of length" (PDF). International Astronomical Union. 2012. "Supplement 2014: Updates to the...
"The astronomicalunit gets fixed: Earth–Sun distance changes from slippery equation to single number". Retrieved 14 Sep 2012. The IAU and astronomical units...
constant of gravitation which allow transformations between astronomicalunits and SI units. Slightly different values for the constants are obtained depending...
The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to...
controversial units Natural unit, a physical unit of measurement Geological unit or rock unit, a volume of identifiable rock or ice Astronomicalunit, a unit of...
in radians per day follows by setting Earth's semi-major axis (the astronomicalunit, au) to unity, k:(rad/d) = (GM☉)0.5·au−1.5. A value of k = 0.01720209895...
community, which adopted the unit and named it after him.[citation needed] It subsequently spread to the fields of astronomical spectroscopy, atomic spectroscopy...
corresponding time unit is the (sidereal) year)), and the mass is the total mass of the Sun (M☉). Astronomicalunit Conversion of units Technically, the...
times Earth's circumference. Around 389 lunar distances make up an AU astronomicalunit (roughly the distance from Earth to the Sun). Lunar distance is commonly...
particles, the solar wind, forming the heliosphere. Around 75–90 astronomicalunits, the solar wind is halted, resulting in the heliopause. This is the...
from the original on 22 October 2008. Retrieved 5 August 2014. One astronomicalunit is currently accepted to be equal to 149597870691±30 m. A light-year...
(GSC) measures the amount of energy received by a given area one astronomicalunit away from the Sun. More specifically, it is a flux density measuring...
the ancient Greeks. Direct distance measurements are based upon the astronomicalunit (AU), which is defined as the mean distance between the Earth and...
the Observatory was the U.S. contribution to the definition of the AstronomicalUnit, or the AU, which defines a standard mean distance between the Sun...
is measured in terms of the semi-major axis of Earth's orbit (the astronomicalunit, AU), time in years, and mass in the total mass of the orbiting system...
a unit of time defined as 365.25 days, each of exactly 86,400 seconds (SI base unit), totaling exactly 31,557,600 seconds in the Julian astronomical year...
of Jupiter, 109 times the radius of the Earth, and 1/215th of an astronomicalunit, the approximate distance between Earth and the Sun. The solar radius...
Atomic units are often abbreviated "a.u." or "au", not to be confused with similar abbreviations used for astronomicalunits, arbitrary units, and absorbance...
10−10 m or 0.1 nanometre. Astronomicalunit, a unit of length used in planetary systems astronomy Arbitrary unit, a placeholder unit for when the actual value...
Engineering on an astronomical scale, or astronomical engineering, i.e., engineering involving operations with whole astronomical objects (planets, stars...
the east, and the z-axis toward the north ecliptic pole; the astronomicalunit is the unit of measure. Symbols for ecliptic coordinates are somewhat standardized;...
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