The latitude of the equator is, by definition, 0°. The length of Earth's equator is about .
The equator is one of the five main circles of latitude that are based on the relationship between the Earth's axis of rotation and the plane of the Earth's orbit around the sun. It 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 movement through the sky, passes directly over the equator twice each year, on the March and September equinoxes. At the equator, the rays of the sun are perpendicular to the surface of the earth on these dates.
Places on the equator experience the quickest rates of sunrise and sunset in the world. Such places also have a theoretical constant 12 hours of day and night throughout the year (in practice there are variations of a few minutes due to the effects of atmospheric refraction and because sunrise and sunset are measured from the time the edge of the Sun's disc is on the horizon, rather than its centre). North or south of the equator day length increasingly varies with the seasons.
Locations near the equator are good sites for spaceports, such as the Guiana Space Centre in Kourou, French Guiana, 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. Spacecraft launched in this manner must launch to the east to use this effect.
For high precision work, the equator is not quite as fixed as the above discussion implies. The true equatorial plane must always be perpendicular to the Earth's spin axis. Although this axis is relatively stable, its position wanders in approximately a radius circular motion each year. Thus, the true equator moves slightly. This, however, is only important for detailed scientific studies. The effect is quite small, and the width of a line marking the equator on almost any map will be much wider than the error.
The surface of the Earth at the equator is mostly ocean. The highest point on the equator is , at 00°00′00″S, 77°59′31″W, on the south slopes of Volcán Cayambe (summit ) in Ecuador. This is a short distance above the snow line, and this point and its immediate vicinity form the only section of the equator where snow lies on the ground.
|long||Country, territory or sea||Notes|
|0°||Atlantic Ocean||Gulf of Guinea|
|7° E||Ilhéu das Rolas|
|8°||Atlantic Ocean||Gulf of Guinea|
|43° 50° 60° 70°||Indian Ocean|
|73°||Passing between Gaafu Dhaalu Atoll and Gnaviyani Atoll|
|80° 90°||Indian Ocean|
|100°||The Batu Islands, Sumatra and the Lingga Islands|
|105°||Indian Ocean||Karimata Strait|
|118°||Indian Ocean||Makassar Strait|
|121°||Indian Ocean||Gulf of Tomini|
|125°||Indian Ocean||Molucca Sea|
|127°||Kayoa and Halmahera islands|
|128°||Pacific Ocean||Halmahera Sea|
|140° 150° 160°||Pacific Ocean|
|173°||Misses every island, passing between Aranuka and Nonouti Atolls|
|176° W|| Baker Island — passes through territorial waters|
The equator also passes through the exclusive economic zones around Howland Island and Jarvis Island, but not through their territorial waters
|170° 160° 150° 140° 130° 120° 110° 100°||Pacific Ocean|
|90°||Isabela Island in the Galápagos Islands|
|80°||The literal translation of Ecuador's official name is "Republic of the Equator"|
|70°||It intersects the country through an Amazon jungle area.|
|60° 50°||Including some islands in the mouth of the Amazon River|
|40° 30° 20° 10°||Atlantic Ocean|
Despite its name, no part of Equatorial Guinea's territory lies on the equator. However, its island of Annobón is about south of the equator, and the rest of the country lies to the north. The country that comes closest to the equator without actually touching it is Peru.
The geographical mile is defined as one arc minute of the equator, and therefore has different values depending on which standard equator is used, namely or for respectively WGS-84 and IAU-2000, a difference of nearly a millimeter.
The earth is standardly modeled as a sphere flattened about 0.336% along its axis. This results in the equator being about 0.16% longer than a meridian (as a great circle passing through the two poles). The IUGG standard meridian is to the nearest millimeter , one arc minute of which is , explaining the SI standardization of the nautical mile as , more than short of the geographical mile.