Editing Astronomical unit (section)

== 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]]&nbsp;(IAU) had used the symbol ''A'' to denote a length equal to the astronomical unit.<ref name="IAU76"/> In the astronomical literature, the symbol AU is common. In 2006, the [[International Bureau of Weights and Measures]] (BIPM) had recommended ua as the symbol for the unit, from the French "unité astronomique".<ref name="Bureau International des Poids et Mesures 2006 126">{{citation |author=Bureau International des Poids et Mesures |author-link=Bureau International des Poids et Mesures |date=2006 |title=The International System of Units (SI) |edition=8th |publisher=Organisation Intergouvernementale de la Convention du Mètre |page=126 |url=http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |archive-date=2022-10-09 |url-status=dead}}</ref> In the non-normative Annex&nbsp;C to [[ISO 80000-3]]:2006 (later withdrawn), the symbol of the astronomical unit was also ua.

In 2012, the IAU, noting "that various symbols are presently in use for the astronomical unit", recommended the use of the symbol "au".<ref name="IAUresB2"/> The [[scientific journal]]s published by the [[American Astronomical Society]] and the [[Royal Astronomical Society]] subsequently adopted this symbol.<ref name="AAS_style">{{cite web |title=Manuscript Preparation: AJ & ApJ Author Instructions |website=American Astronomical Society |url=http://aas.org/authors/manuscript-preparation-aj-apj-author-instructions#_Toc2.2 |access-date=29 October 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160221121728/http://aas.org/authors/manuscript-preparation-aj-apj-author-instructions#_Toc2.2 |archive-date=21 February 2016 |quote=Use standard abbreviations for ... natural units (e.g., au, pc, cm).}}</ref><ref>{{cite web |title=Instructions to Authors |website=Monthly Notices of the Royal Astronomical Society |publisher=Oxford University Press |url=https://academic.oup.com/mnras/pages/General_Instructions |access-date=5 November 2020 |quote=The units of length/distance are Å, nm, µm, mm, cm, m, km, au, light-year, pc.}}</ref> In the 2014 revision and 2019 edition of the SI Brochure, the BIPM used the unit symbol "au".<ref name=SI_Brochure2012>{{cite web |orig-year=2006 |year=2014 |title=The International System of Units (SI) |edition=8th |publisher=BIPM |series=SI Brochure |url=http://www.bipm.org/en/publications/si-brochure/table6.html |access-date=3 January 2015}}</ref><ref name=SI_Brochure2019>{{cite web |url=https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-EN.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-EN.pdf |archive-date=2022-10-09 |url-status=live |series=SI Brochure |title=The International System of Units (SI) |edition=9th |year=2019 |publisher=BIPM |page = 145 |access-date=1 July 2019}}</ref> ISO&nbsp;80000-3:2019, which replaces ISO&nbsp;80000-3:2006, does not mention the astronomical unit.<ref>{{cite web |title=ISO 80000-3:2019 |date=19 May 2020 |url=https://www.iso.org/standard/64974.html |publisher=[[International Organization for Standardization]] |access-date=2020-07-03}}</ref><ref>{{cite web |id=ISO&nbsp;80000-3:2019(en) |series=Quantities and units |title=Part&nbsp;3: Space and time |url=https://www.iso.org/obp/ui/#iso:std:iso:80000:-3:ed-2:v1:en |publisher=[[International Organization for Standardization]] |access-date=2020-07-03}}</ref>