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The siriometer is an obsolete astronomical unit of length, defined to be equal to one million astronomical units (au).[1] One siriometer is approximat ly 149.6 petametres; 4.848 parsecs; 15.81 light-years. The distance from Earth to the star Sirius is then approximately 0.54 siriometers.[2]

The unit was proposed[why?] in 1911 by Carl V. L. Charlier who used the symbol 'sir.'[1] Others have suggested denoting the unit with the symbol 'Sm'.[citation needed]

The siriometer never gained widespread usage; the first General Assembly of the International Astronomical Union in 1922 adopted the parsec as the standard unit of stellar distances,[3] which simplified the definition of absolute magnitude.[2] Use of the siriometer seems to have disappeared from the astronomical literature by c. 1930.[2] Professional astronomers use the parsec as their primary unit of distances larger than the Solar System.

Further reading[edit]

  • Arenou, Frédéric. "The origin of the parsec". Paris Observatory. Retrieved 18 May 2018.


  1. ^ a b Charlier, C. V. L. (1921). Lectures on Stellar Statistics.
  2. ^ a b c Beech, Martin (2008). "The reluctant parsec and the overlooked light-year". The Observatory. 128: 489. Bibcode:2008Obs...128..489B.
  3. ^ Malmquist, K. G. (1925). "On the units of distance in stellar astronomy". The Observatory. 48: 142. Bibcode:1925Obs....48..142M.