- the great circle on a sphere or heavenly body whose plane is perpendicular to the axis, equidistant everywhere from the two poles of the sphere or heavenly body.
- the great circle of the earth that is equidistant from the North Pole and South Pole.
- a circle separating a surface into two congruent parts.
- celestial equator.
- the great circle of the earth with a latitude of 0°, lying equidistant from the poles; dividing the N and S hemispheres
- a circle dividing a sphere or other surface into two equal symmetrical parts
- See magnetic equator
- astronomy See celestial equator
