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Parsec - Wikipedia. The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System.One parsec is approximately equal to 31 trillion kilometres (3.1 × 10 13 km), 19 trillion miles (1.9 × 10 13 mi), or 206,265 astronomical units (au), and equates to about 3.26 light-years.A parsec is obtained by the use of parallax and ...