1. The great circle around the earth that lies in a plane perpendicular to the earth's axis. It is equidistant from the two geographical poles.
2. The magnetic equator is a line of zero magnetic dip (see geomagnetism) that is close to the geographical equator but lies north of it in Africa and south of it in America.
3. The celestial equator is the circle formed on the celestial sphere by the extension of the earth's equatorial plane.