The siriometer is an obsolete astronomical unit of length, defined to be equal to one million astronomical units (au).[1][2] One siriometer is approximately 149.6 petametres; 4.848 parsecs; 15.81 light-years. The distance from Earth to the star Sirius is then approximately 0.54 siriometers.[3]

The unit was proposed in 1911 by Carl V. L. Charlier,[3] who worked on stellar statistics.[4] Charlier originally used the symbol 'sir'[1] but the symbol 'Sm' has also seen use.[5]

The siriometer never gained widespread usage. Frank Dyson (the Astronomer Royal) objected to the name siriometer, because "it suggests a machine for measuring".[6] The first General Assembly of the International Astronomical Union in 1922 adopted the parsec as the standard unit of stellar distances,[7] which simplified the definition of absolute magnitude.[3] Use of the siriometer seems to have disappeared from the astronomical literature by c. 1930.[3] Modern professional astronomers use the parsec as their primary unit for distances larger than the Solar System.

Further reading

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

References

  1. 1 2 Charlier, C. V. L. (1921). Lectures on Stellar Statistics. Bibcode:1921lss..book.....C.
  2. ↑ Charlier, C. V. L. (May 1913). "An Investigation on the Motion of the Stars". Monthly Notices of the Royal Astronomical Society. 73 (7): 486–492. Bibcode:1913MNRAS..73..486C. doi:10.1093/mnras/73.7.486. I have used ... the term "Siriometer" for denoting a distance equal to a million times the mean distance of the Sun from the Earth.
  3. 1 2 3 4 Beech, Martin (2008). "The reluctant parsec and the overlooked light-year". The Observatory. 128: 489. Bibcode:2008Obs...128..489B.
  4. ↑ "Astronomy in Sweden 1860-1940". www.astro.uu.se. Retrieved 2021-02-28.
  5. ↑ "units". nrc-cnrc.github.io. Retrieved 2023-03-31.
  6. ↑ "Meeting of the Royal Astronomical Society. Friday, 1913 March 14". The Observatory. 36 (460): 160. April 1913. Bibcode:1913Obs....36..160.
  7. ↑ Malmquist, K. G. (1925). "On the units of distance in stellar astronomy". The Observatory. 48: 142. Bibcode:1925Obs....48..142M.


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