(pc) A basic unit of stellar distance, corresponding to a trigonometric parallax of one second of arc (1″). In other words, it is the distance at which one astronomical unit subtends an angle of one second of arc. One parsec equals 3.2616 light years, 206 265 astronomical units, or 30.857 × 1012 km. For distances on galactic and intergalactic scales, kiloparsec (kpc) and megaparsec (Mpc) are used. See also light year.