An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and midway between the poles. The Equator usually refers to the Earth's equator: an imaginary line on the Earth's surface equidistant from the North Pole and South Pole, dividing the Earth into the Northern Hemisphere and Southern Hemisphere. Other planets and astronomical bodies have equators similarly defined. The Equator is about 40,075 kilometres (24,901 mi) long; 78.7% is across water and 21.3% is over land.
The latitude of the Equator is by definition 0° (zero degrees). The Equator is one of the five notable circles of latitude on Earth, with the others being the two Polar Circles and the two Tropical Circles: the Tropic of Cancer and the Tropic of Capricorn. The Equator is the only line of latitude which is also a great circle. The imaginary circle obtained when the Earth's equator is projected onto the sky is called the celestial equator.
In its seasonal apparent movement across the sky the sun passes over the Equator twice each year, at the March and September equinoxes. At the moment of the equinox, light rays from the center of the sun are perpendicular to the surface of the earth at the point on the equator experiencing solar noon.