A coordinate system which is centered at theSun and is "fixed" with respect to the synodic rotation rate; the meansynodic value is about 27.2753 days. The Astronomical Almanac gives a valuefor Carring
ton longitude of 349.03 degrees at 0000 UT on 1 January 1995.
Carrington heliographic coordinates One of two heliographic coordinate systems used for identifying the position of features on the Sun's surface. In the Carrington system, lines of longitude rotate w
ith the Sun. A prime meridian, analogous to the Greenwich meridian on Earth, was defined to coincide with the central meridian of the Sun (as seen from Earth) at a specific time on 1853November9 when R. C.Carrington began his observations. A new Carrington rotation begins each time the prime meridian crosses the central meridian. The rotation period of the coordinate system varies throughout the year because of the changing distance of the Earth from the Sun, with an average value of 27.2753 days (the mean synodic period). This corresponds to a sidereal rotation period of 25.38 days. The Carrington longitude of the central meridian is 360� at the beginning of the Carrington rotation, and decreases to zero at the end. The longitude of a feature on the Sun (such as a sunspot) remains approximately constant in the Carrington system, in contrast to the Stonyhurst system.
A system of fixed solar longitudes rotating at a uniform synodic period of 27.2753 days (a sidereal period of 25.38 days). Carrington selected the meridian that passed through the ascending node of th
e Sun’s equator at 1200 UTC on 1 January 1854 as the original prime meridian. The daily Carrington longitude of the central point of the apparent solar disk is listed (with other solar coordinates) in The Astronomical Almanac published annually by the U.S. Naval Observatory. Compare Bartels’ rotation number.