The siriometer is an obsolete astronomical unit of length, defined to be equal to one million astronomical units (au). 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.
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, which simplified the definition of absolute magnitude. Use of the siriometer seems to have disappeared from the astronomical literature by c. 1930. Professional astronomers use the parsec as their primary unit of distances larger than the Solar System.
- Charlier, C. V. L. (1921). Lectures on Stellar Statistics. Bibcode:1921lss..book.....C.
- Beech, Martin (2008). "The reluctant parsec and the overlooked light-year". The Observatory. 128: 489. Bibcode:2008Obs...128..489B.
- Malmquist, K. G. (1925). "On the units of distance in stellar astronomy". The Observatory. 48: 142. Bibcode:1925Obs....48..142M.
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