Equator
Overview
The latitude of the Earth's equator is, by definition, 0° (zero degrees) of arc. The equator is one of the five notable circles of latitude on Earth; the other four are both polar circles (the Arctic Circle and the Antarctic Circle) and both 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—that is, one whose plane passes through the center of the globe. The plane of Earth's equator, when projected outwards to the celestial sphere, defines the celestial equator.
Equator-4