FANDOM


Astronomical unit

The red line indicates the Earth–Sun distance, which on average is about 1 astronomical unit.

The astronomical unit (symbol: au[1][2][3] or ua[4]) is a unit of length roughly the distance from Earth to the Sun. 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, it is since 2012 defined as exactly 149,597,870,700 metres (about 150 million kilometres, or 93 million miles).[5] The astronomical unit is used primarily as a convenient yardstick for measuring distances within the Solar System or around other stars. However, it is also a fundamental component in the definition of another unit of astronomical length, the parsec.

ReferencesEdit

  1. International Astronomical Union, ed. (31 August 2012), "RESOLUTION B2 on the re-definition of the astronomical unit of length", RESOLUTION B2, Beijing, China: International Astronomical Union, http://www.iau.org/static/resolutions/IAU2012_English.pdf, "The XXVIII General Assembly of International Astronomical Union … recommends … 5. that the unique symbol "au" be used for the astronomical unit." 
  2. "Monthly Notices of the Royal Astronomical Society: Instructions for Authors". Oxford Journals. http://www.oxfordjournals.org/our_journals/mnras/for_authors/#6.4%20Miscellaneous%20journal%20style. Retrieved 2015-03-20. ""The units of length/distance are Å, nm, µm, mm, cm, m, km, au, light-year, pc." 
  3. "Manuscript Preparation: AJ & ApJ Author Instructions". American Astronomical Society. http://aas.org/authors/manuscript-preparation-aj-apj-author-instructions#_Toc2.2. Retrieved 2016-10-29. ""Use standard abbreviations for SI... and natural units (e.g., au, pc, cm)."" 
  4. ISO 80000-3, Quantities and units – Space and time
  5. International Astronomical Union, ed. (31 August 2012), "RESOLUTION B2 on the re-definition of the astronomical unit of length", RESOLUTION B2, Beijing, Kina: International Astronomical Union, http://www.iau.org/static/resolutions/IAU2012_English.pdf, "The XXVIII General Assembly of International Astronomical Union 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"