|
Longitude measured for points on the Sun. There is no fixed zero point on the Sun so heliographic longitude is measured from a nominal reference great circle: the solar meridian that passed through the ascending node of the solar equator on the ecliptic on 1 January 1854 at 12.00 UT. Relative to this, longitude is calculated by assuming a uniform sidereal rotation rate of 25.38 days. Tables published in observing handbooks are used by solar observers to determine the position of the solar reference meridian for a given date and time.
|