Heliographic Coordinates

heliographic latitude and longitude, magnitudes used to determine positions of points on the surface of the sun. The heliographic latitude is the angular distance of a given point from the solar equator measured along a solar meridian. Heliographic longitude is the angle between the plane of the meridian of a given point and the plane of the zero meridian, taken to be the so-called Carrington meridian, which crosses the ascending node of the solar equator at the mean Greenwich noon of Jan. 1, 1854. Astronomical almanacs give for each day the data (the heliographic coordinates of the apparent center of the sun, the orientation of its axis of rotation), needed to determine the heliographic coordinates of any point on the surface of the sun.