Heliographic - A heliocentric rotatingcoordinate system where the Z axis is normal to the solar equatorial plane,positive northward. X, Y axes rotate with a 25.38 day period. The zerolongitude (X axis
) is defined as the longitude that passed through theascending node of the solar equator on the ecliptic plane on 1 January, 1854at 12 UT. See
Physical features on the surface of the Sun are located in Heliographic coordinates (Expl.Suppl., 1961,11.B). Heliographic latitude is measured from the solar equator positive towards North, Heliograp
hic longitude
is defined westward (i.e. in the direction of planetary motion) from the solar prime meridian which passed through the ascending node on the ecliptic of date on 1854 Jan 1, noon (JD 239 8220.0). Heliographic
longitude is sometimes identified with Carrington longitude, but this usage should be avoided since there have been different definitions of the later term over time.
XY-plane: Solar equator of date
+X-axis: ascending node on 1854 Jan 1, noon (JD 239 8220.0)
Angles: Heliographic latitude Y and longitude F right handed.
Heliographic Inertial - A heliocentriccoordinate system where the Z axis is normal to the solar equatorial plane,positive northward. X axis is along the intersection line between solarequatorial and e
cliptic planes. The X axis was positive at SE longitude of74.367 deg on Jan 1, 1900. (See SE below.) See