What is “parsec“?

The parsec is a unit for expressing distances to stars and galaxies. It is used by professional astronomers. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond.

This means that a star at a distance of one parsec would have a parallax of one second, and the distance of an object in parsecs is the reciprocal of its parallax in seconds of arc.

Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun.

For example, the nearest star, Proxima Centauri, which is part of the Alpha Centauri triple-star system, has a parallax of 0.769 second of arc, and, hence, its distance from the Sun and Earth is 1.30 parsec. One parsec equals 3.26 light-years, which is equivalent to 3.09 × 1013 km.

It is useful to know that one parsec equals the following:


yard (yd) 3.3745380173090856*1016
foot (ft) 1.0123614086089778*1017
span 1.3498175573091365*1017
hand 3.037084195080665*1017
inch (in) 1.2148336927904748*1018
line 1.4578004313485697*1019
mil 1.215*1021


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