- published: 18 Jun 2013
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An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass.
The Equator refers to the Earth's equator and is 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 spherical astronomical bodies have equators similarly defined.
The latitude of the Equator is 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.
The Sun, in its seasonal apparent movement across the sky, passes directly over the Equator twice each year, at the March and September equinoxes. At the Equator, the rays of the sun are perpendicular to the surface of the earth on these dates.