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The equator is the only line of latitude which is also a great circle—meaning, 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 .
The fundamental plane and the primary direction mean that the coordinate system, while aligned with Earth's equator and pole, does not rotate with the Earth, but remains relatively fixed against the background stars. A right-handed convention means that coordinates increase northward from and eastward around the fundamental plane.
A geographical mile is defined to be the length of one minute of arc along the equator (one equatorial minute of longitude) therefore a degree of longitude along the equator is exactly 60 geographical miles or 111.3 kilometers, as there are 60 minutes in a degree. The length of 1 minute of longitude along the equator is 1 geographical mile or 1 ...
The definition of geodetic latitude (ϕ) and geocentric latitude (θ) The geocentric latitude is the angle between the equatorial plane and the radius from the centre to a point of interest. When the point is on the surface of the ellipsoid, the relation between the geocentric latitude (θ) and the geodetic latitude (ϕ) is:
The equator is the circle that is equidistant from the North Pole and South Pole. It divides the Earth into the Northern Hemisphere and the Southern Hemisphere . Of the parallels or circles of latitude, it is the longest, and the only ' great circle ' (a circle on the surface of the Earth, centered on Earth's center).
In other words, the equinoxes are the only times when the subsolar point is on the equator, meaning that the Sun is exactly overhead at a point on the equatorial line. The subsolar point crosses the equator moving northward at the March equinox and southward at the September equinox.
The equivalent line of latitude south of the Equator is called the Tropic of Capricorn, and the region between the two, centered on the Equator, is the tropics. In the year 2000, more than half of the world's population lived north of the Tropic of Cancer.
Geodetic latitude and geocentric latitude have different definitions. Geodetic latitude is defined as the angle between the equatorial plane and the surface normal at a point on the ellipsoid, whereas geocentric latitude is defined as the angle between the equatorial plane and a radial line connecting the centre of the ellipsoid to a point on the surface (see figure).