# parsec

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## parsec

(pär`sĕc) [parallax + second], in astronomy, basic unit of length for measuring interstellar and intergalactic distances, equal to 206,265 times the distance from the earth to the sun, 3.26 light-years, or 3.08 × 1013 km (about 19 million million mi). The distance in parsecs of an object from the earth is the reciprocal of the parallaxparallax
, any alteration in the relative apparent positions of objects produced by a shift in the position of the observer. In astronomy the term is used for several techniques for determining distance.
of the object. The nearest star, Proxima Centauri, has a parallax of 0.763" of arc and a distance of about 1.31 parsecs.

## parsec

(par -sek) Short for parallax second. Symbol: pc. A unit of length normally used for distances beyond the Solar System. It is the distance at which the semimajor axis of the Earth's orbit subtends an angle of one arc second. It is thus the distance at which a star would have an annual parallax of one arc second. A star with a parallax of p arc seconds is at a distance of d parsecs, given by d = 1/p (accurate up to distances of about 30 pc). One parsec equals 30.857 × 1012 km, 206 265 astronomical units, and 3.2616 light-years.

## Parsec

a unit of distance in astronomy equal to 206,265 astronomical units, or 30,857 X 1012 km; its international abbreviation is pc. Distance expressed in parsecs is the reciprocal of the annual parallax. Thus, a distance of 10 pc corresponds to a parallax of 0.1”. In fact, the name “parsec” derives from these last two values—”parallax of one second.” One parsec is equal to 3.26 light-years.

## parsec

[′pär‚sek]
(astronomy)
The distance at which a star would have a parallax equal to 1 second of arc; 1 parsec equals 3.258 light-years or 3.08572 × 1013 kilometers. Derived from parallax-second.

## parsec

a unit of astronomical distance equal to the distance from earth at which stellar parallax would be 1 second of arc; equivalent to 3.0857 × 1016 m or 3.262 light years

## PARSEC

Extensible language with PL/I-like syntax, derived from PROTEUS. "PARSEC User's Manual", Bolt Beranek & Newman (Dec 1972).
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