In geography, the equator is an imaginary line drawn around a planet, halfway between the poles, where the surface of the roughly spherical planet is parallel to the axis of rotation. The equator divides the surface into the Northern hemisphere and the Southern hemisphere. The latitude of the equator is 0 by definition. The length of Earth's equator is about 40070 km.

On the equator, the Sun is directly overhead at noon on the days of the equinox. Furthermore, every day is close to 12 hours long there. At night, all stars appear to trace out a half circle centered at the southernmost or northernmost point of the horizon.

Between the March and September equinox, the Earth's northern latitudes are inclined towards the Sun up to a point known as the Tropic of Cancer, the most northerly point where the Sun can be directly overhead. The most southerly equivalent reached between the September and March equinox is named the Tropic of Capricorn.

Seasons in the tropics and at the equator differ significantly from seasons in the temperate zones. In many tropical regions people identify two seasons, wet and dry. On the equator, seasons can vary depending on a variety of factors including elevation and proximity to an ocean.

Locations near the equator are good sites for potential spaceports or space elevators, as they are already moving faster than any other point on the Earth due to the Earth's rotation, and the added velocity reduces the amount of fuel needed to launch spacecraft. (See Kourou for an example).

The surface of the Earth at the equator is mainly ocean. Places crossed by the equator: