| Term: | HeliocentricAriesEclipticCoordinateSystem |
| Definition: |
This system has its Z axis perpendicular to the plane of the Earth's orbit around the Sun (positive North) and its X axis towards the First Point of Aries (the direction in space defined by the intersection between the Earth's equatorial plane and the plane of its orbit around the Sun (the plane of the ecliptic). This system is (to first order) fixed with respect to the distant stars. It is subject to slow change owing to the various slow motions of the Earth's rotation axis with respect to the fixed stars. |