The siriometer is a rarely used astronomical measure equal to one million astronomical units, i.e., one million times the average distance between the Sun and Earth. This distance is equal to about 149,597,870,000,000,000 meters (149.6 Pm) or about 15.813 light-years, which is roughly twice the distance from Earth to the star Sirius.
It was proposed in 1911 by Carl V. L. Charlier.
The proposed symbol for the siriometer is (Sm).
References
Siriometer Wikipedia(Text) CC BY-SA