Editing Speed of light (section)

==== Astronomical unit ====
{{main|Astronomical unit}}
Historically the speed of light was used together with timing measurements to determine a value for the  astronomical unit (AU).<ref>{{Cite journal |last=Standish |first=E. M. |date=June 2004 |title=The Astronomical Unit now |url=https://www.cambridge.org/core/product/identifier/S1743921305001365/type/journal_article |journal=Proceedings of the International Astronomical Union |language=en |volume=2004 |issue=IAUC196 |pages=163–179 |doi=10.1017/S1743921305001365 |issn=1743-9213}}</ref> It was redefined in 2012 as exactly {{val|149597870700|u=m}}.<ref>{{Cite journal|journal=The International System of Units|title=Supplement 2014: Updates to the 8th edition (2006) of the SI Brochure|url=http://www.bipm.org/utils/common/pdf/si_supplement_2014.pdf|year=2014|publisher= International Bureau of Weights and Measures|page=14}}</ref><ref name=AU_redef>{{Cite web|title=Resolution B2 on the re-definition of the astronomical unit of length|url=https://www.iau.org/static/resolutions/IAU2012_English.pdf|year=2012|publisher=International Astronomical Union}}</ref> This redefinition is analogous to that of the metre and likewise has the effect of fixing the speed of light to an exact value in astronomical units per second (via the exact speed of light in metres per second).<ref>{{Cite journal|last=Brumfiel|first=Geoff|date=14 September 2012|title=The astronomical unit gets fixed|url=https://www.nature.com/articles/nature.2012.11416|journal=[[Nature (journal)|Nature]]|language=en|doi=10.1038/nature.2012.11416|s2cid=123424704|issn=1476-4687}}</ref>