what is an equator

The equator is an imaginary line that circles the middle of a planet or other celestial body, dividing it into the northern and southern hemispheres. On Earth, it is located at 0 degrees latitude and is about 40,075 km in circumference. It is a circle of latitude that is equidistant from the poles and lies in a plane perpendicular to the Earths axis. The equator is one of the five notable circles of latitude on Earth; the other four are the two polar circles (the Arctic Circle and the Antarctic Circle) and the two tropical circles (the Tropic of Cancer and the Tropic of Capricorn) . The equator is used as a reference line from which latitude is reckoned. The celestial equator is the great circle in which the plane of the terrestrial equator intersects the celestial sphere, and it is equidistant from the celestial poles.