| the great circle of the celestial sphere, lying in the same plane as the earth's equator. |
| celestial equator n. A great circle on the celestial sphere in the same plane as the earth's equator. Also called equinoctial, equinoctial circle. |
| celestial equator
A great circle separating the northern and southern hemispheres of the celestial sphere and lying in the same plane as the Earth's equator. The celestial equator is a projection of the Earth's equator outward onto the celestial sphere and is used as the reference point in determining a celestial body's declination. |
