| definition |
- Heliographic - A heliocentric rotating coordinate 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 zero
longitude (X axis) is defined as the longitude that passed through the ascending node of the
solar equator on the ecliptic plane on 1 January, 1854 at 12 UT. See
.
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