A parsec (symbol: pc) is a unit of length used to measure large distances to objects outside the Solar System. One parsec is the distance at which one astronomical unitsubtends an angle of one arcsecond. A parsec is equal to about 3.26 light-years (31 trillionkilometres or 19 trillion miles) in length. The nearest star, Proxima Centauri, is about 1.3 parsecs from the Sun. Most of the stars visible to the unaided eye in the nighttime sky are within 500 parsecs of the Sun.