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 or , i. e. . Parsec is obtained by the use of parallax and trigonometry, and is defined as the distance at which one astronomical unit subtends an angle of one arcsecond ( of a degree). This corresponds to astronomical units, i.e. . The nearest star, Proxima Centauri, is about from the Sun. Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun.