A parsec (symbol: pc) is a unit of length used to measure large distances to objects outside our Solar System. One parsec is the distance at which one astronomical unit subtends an angle of one arcsecond. A parsec is equal to about 3.26 light-years (31 trillion kilometres 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 nighttime sky are within 500 parsecs of the Sun.