Siriometer
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
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References
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