Equator

It is an imaginary line located at 0 degrees latitude, about 40,075 km (24,901 mi) in circumference, halfway between the North and South poles.

In the cycle of Earth's seasons, the equatorial plane runs through the Sun twice a year: on the equinoxes in March and September.

Locations on the equator experience the shortest sunrises and sunsets because the Sun's daily path is nearly perpendicular to the horizon for most of the year.

The added velocity reduces the fuel needed to launch spacecraft eastward (in the direction of Earth's rotation) to orbit, while simultaneously avoiding costly maneuvers to flatten inclination during missions such as the Apollo Moon landings.

[4] The precise location of the equator is not truly fixed; the true equatorial plane is perpendicular to the Earth's rotation axis, which drifts about 9 metres (30 ft) during a year.

The GRS 80 (Geodetic Reference System 1980) as approved and adopted by the IUGG at its Canberra, Australia meeting of 1979 has an equatorial radius of 6,378.137 km (3,963.191 mi).

The WGS 84 (World Geodetic System 1984) which is a standard for use in cartography, geodesy, and satellite navigation including GPS, also has an equatorial radius of 6,378.137 km (3,963.191 mi).

France, Norway (Bouvet Island), and the United Kingdom are the other three Northern Hemisphere-based countries which have territories in the Southern Hemisphere.

Throughout the year, the Northern and Southern hemispheres are alternately turned either toward or away from the Sun, depending on Earth's position in its orbit.

Near the equator, this means the variation in the strength of solar radiation is different relative to the time of year than it is at higher latitudes: maximum solar radiation is received during the equinoxes, when a place at the equator is under the subsolar point at high noon, and the intermediate seasons of spring and autumn occur at higher latitudes; and the minimum occurs during both solstices, when either pole is tilted towards or away from the sun, resulting in either summer or winter in both hemispheres.

Nevertheless, temperatures are high year-round due to the Earth's axial tilt of 23.5° not being enough to create a low minimum midday declination to sufficiently weaken the Sun's rays even during the solstices.

Despite high year-round sea level temperatures, some higher altitudes such as the Andes and Mount Kilimanjaro have glaciers.

[citation needed] Milder line-crossing ceremonies, typically featuring King Neptune, are also held for passengers' entertainment on some civilian ocean liners and cruise ships.

Countries and territories that are intersected by the equator (red) or the Prime Meridian (blue), which intersect at " Null Island ".
The equator during the boreal winter, spanning from December to March.
The equator marked as it crosses Ilhéu das Rolas , in São Tomé and Príncipe
The Marco Zero monument marking the equator in Macapá , Brazil
GPS reading taken on the equator close to the Quitsato Sundial , in Cayambe , Ecuador [ 8 ]
Sign on the equator in San Antonio de Pichincha , Ecuador.
The N1 road crossing the equator in Gabon , north of Bifoun .

Diagram of the seasons, showing the situation at the December solstice. Regardless of the time of day (i.e. Earth 's rotation on its axis), the North Pole will be dark, and the South Pole will be illuminated; see also polar night . In addition to the density of incident light, the dissipation of light in atmosphere is greater when it falls at a shallow angle.