天文單位

天文單位（粵拼：tin1 man4 daan1 wai2）係個長度單位，大約係地球同太陽之間嘅遠。以前曾經定佢係1495億9787萬0691米，上下差30米，即係大約1億5千萬千米。喺2012年8月嘅國際天文學大會（IAU）第28屆全體會議入面，天文學家投票將天文單位固定咗喺149,597,870,700米^[1]。由嗰時起天文單位唔再同地球同太陽之間嘅實際距離掛鈎。

基礎

睇埋：地球軌道

天文單位個名由英文 astronomical unit 譯過來，符號AU、au、a.u.或者ua等等。

測量

使用

歷史

註

1. International Astronomical Union, 編 (31 August 2012), "RESOLUTION B2 on the re-definition of the astronomical unit of length" (PDF), RESOLUTION B2, Beijing, Kina: International Astronomical Union, 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 7011149597870700000♠149597870700 metres, in agreement with the value adopted in IAU 2009 Resolution B2

出面網頁

• Chasing Venus, Observing the Transits of Venus Smithsonian Institution Libraries
• Units outside the SI (at the NIST web site)
• Recommendations concerning Units (at the IAU web site)
• Solar Mass Loss, the Astronomical Unit, and the Scale of the Solar System (a discussion of the relation between the AU and other quantities)