<Tr> <Th> imperial & US units </Th> <Td> 7016308575618560000 ♠ 1.9174 × 10 mi </Td> </Tr> <Tr> <Th> astronomical units </Th> <Td> 7016308568047999355 ♠ 2.062 65 × 10 au 7016308567400801506 ♠ 3.261 56 ly </Td> </Tr> <P> The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System . A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond, which corresponds to 7005648000000000000 ♠ 648 000 / π astronomical units . One parsec is equal to about 3.26 light - years (30 trillion km or 19 trillion miles) in length . The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 light - years) from the Sun . Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun . </P> <P> The parsec unit was probably first suggested in 1913 by the British astronomer Herbert Hall Turner . Named as a portmanteau of the parallax of one arcsecond, it was defined so as to make calculations of astronomical distances quick and easy for astronomers from only their raw observational data . Partly for this reason, it is the unit preferred in astronomy and astrophysics, though the light - year remains prominent in popular science texts and common usage . Although parsecs are used for the shorter distances within the Milky Way, multiples of parsecs are required for the larger scales in the universe, including kilo parsecs (kpc) for the more distant objects within and around the Milky Way, mega parsecs (Mpc) for mid-distance galaxies, and giga parsecs (Gpc) for many quasars and the most distant galaxies . </P>

How many astronomical units are in one parsec