astronomical unit

Definition from Wiktionary, the free dictionary
Jump to: navigation, search



astronomical unit ‎(plural astronomical units)

  1. (astronomy) The mean distance from the Earth to the Sun (the semi-major axis of Earth's orbit), approximately 149,600,000 kilometres (symbol AU), used to measure distances in the solar system.
    • 2000 April 10, Joe LeSearne, “Zeta 2 Reticuli : Home System Of The Greys?”, in[1], retrieved 2012-08-05:
      Now this big quarter of a Jupiter mass planet is in an orbit about Zeta 2 Reticuli which lasts 18.9 days and has a Semi-Major Axis of 0.14 Astronomical Unit (AU). For comparison Mercury has a Semi-Major Axis of 0.387 AU equal to 36 million miles and Earth has a Semi-Major Axis of 1.00 AU equal to 92.9 million miles. Now if we assume that this newly discovered planet, which we will name Reticulum 1 in accordance with Bob Lazar’s convention, is the closest one to Zeta 2 Reticuli (it’s hard to imagine a closer one), then following Bode’s Law (the law which states each planet is about twice the distance from it’s sun as its inner neighbor) Reticulum 2 should be at 0.28 AU, Reticulum 3 should be at 0.56 AU and, INTERESTINGLY, Reticulum 4 would be at 1.12 AU in between the Earth’s 1.00 AU and Mars’s 1.52 AU, well within the “life-zone” of a G class star!


  • A.U., a.u. (common abbreviation)
  • AU (common unit symbol)
  • au (IAU recommended unit symbol)
  • ua (BIPM recommended unit symbol)
  • (Unicode unit symbol glyph)
  • a. u., A. U. (formerly common abbreviation)