Ækvator

ækvator is the imaginary line encircling a planet that is equidistant from its poles, lying in a plane perpendicular to the rotation axis. On Earth, it is defined as 0 degrees latitude and divides the planet into the Northern and Southern Hemispheres. It is a great circle, meaning it represents the largest possible circle that can be drawn on the surface of a sphere.

Earth’s equatorial circumference is about 40,075 kilometers, and its equatorial radius is approximately 6,378.137 kilometers. Because Earth is an oblate spheroid, equatorial circles at other latitudes are shorter than the circumference at the equator. The concept of an equator applies to other planets as well, with the length and orientation depending on each body's shape and rotation.

In geography and navigation, the equator serves as the reference line for zero latitude. The celestial equator is the projection of Earth’s equator onto the celestial sphere and provides a reference for the celestial coordinate system used in astronomy. The term ækvator appears as a spelling variant in some languages, and its etymology traces to Latin aequator, from aequare, meaning to make level or equal.