The English used in this article may not be easy for everybody to understand. (November 2011)
The ecliptic is the apparent path that the Sun traces out in the sky during the year. As it appears to move in the sky in relation to the stars, the apparent path aligns with the planets throughout the course of the year. It is the intersection of a spherical surface, the celestial sphere, with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun.
The ecliptic plane should be distinguished from the invariable plane. This is the average plane of the orbits of the planets. More precisely, it is perpendicular to the vector sum of the angular momenta of all planetary orbital planes, to which Jupiter is the main contributor. The present ecliptic plane is inclined to the invariable ecliptic plane by about 1.5°.
The name ecliptic is derived from being the place where eclipses occur.