A system for identifying individual rotations of the Sun. On this system the Sun is assigned a sidereal rotation period of 25.38 days. The synodic period of a Carrington rotation varies slightly during the year because of the changing speed of the Earth in its orbit, but averages 27.2753 days. Carrington rotation no. 1 began on 1853 November 9. The system was originated by R. C. Carrington.