Heliocentric Earth Ecliptic - A coordinatesystem where the Z axis is normal to the ecliptic plane, positive northward.X axis points from Sun to Earth. See Hapgood, 1992
Heliocentric Earth Equatorial - A coordinatesystem where the Z axis is normal to the solar equatorial plane, positivenorthward. X axis is generally Earthward in the plane defined by the Z axisand the
Sun-Earth direction. See Hapgood, 1992.