Parsec Parsec The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond, which corresponds to astronomical units. One parsec is equal to about 3.26 light-years (30 trillion km or 19 trillion miles) in length. 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. The parsec unit was probably first suggested in
Unit distance graph pairs might also be at unit distance apart. For instance, the Möbius-Kantor graph has a drawing of this type. According to this looser definition of a unit distance graph, all generalized Petersen graphs are unit distance graphs . In order to distinguish the two definitions, the graphs in which non-edges are required to be a non-unit distance apart may be called strict unit distance graphs . The graph formed by removing one of the spokes from the wheel graph "W" is a subgraph of a unit distance graph, but is not a strict unit distance graph: there is only one