ecliptic coordinate system

The ecliptic coordinate system is a celestial coordinate system based on the ecliptic, the Sun's path around the celestial sphere as seen from Earth. Typically, spherical coordinates analogous to latitude and longitude are used:

• ecliptic latitude.
• ecliptic longitude.
• ecliptic - defines the ecliptic latitude of 0 degrees, analogous to 0 degrees (ordinary) latitude being the equator.
• vernal equinox - used analogously to the Greenwich meridian, i.e., it marks the ecliptic longitude of 0 degrees.

Its poles are termed the ecliptic poles, the ecliptic north pole being the direction perpendicular to the ecliptic nearer to north along Earth's axis.

Rectangular ecliptic coordinates are sometimes used, usually using the ecliptic as the X-Y plane, and the vernal equinox as the X axis. Coordinates are three dimensional (X,Y,Z), which effectively specify a radius, i.e., distance to the object. If the distance to the object is not intended to be specified, the coordinates can be cited such that the radius is 1.

The vernal equinox shifts with the precession of the equinoxes, so the coordinates are useful only if a specific point in time (epoch) is specified. Such a system seems useful regarding specification of the positions of solar system objects at given times. The system is sometimes used in relation a theoretical observer at the Sun rather than on Earth.