Parsec

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The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years, 206,265 astronomical units (au), or 30.9 trillion kilometres (19.2 trillion miles). The parsec unit is obtained by the use of parallax and trigonometry, and is defined as the distance at which 1 au subtends an angle of one arcsecond (⁠1/3600⁠ of a degree). The nearest star, Proxima Centauri, is about 1.3 parsecs (4.2 light-years) from the Sun: from that distance, the gap between the Earth and the Sun spans slightly less than one arcsecond. Most stars visible to the naked eye are within a few hundred parsecs of the Sun, with the most distant at a few thousand parsecs, and the Andromeda Galaxy at over 700,000 parsecs (2,283,000 ly). The word parsec is a shortened form of a distance corresponding to a parallax of one arcsecond, coined by the British astronomer Herbert Hall Turner in 1913. The unit was introduced to simplify...

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