Earth's rotation, internal density variations, and external tidal forces cause its shape to deviate systematically from a perfect sphere. Local topography increases the variance, resulting in … See more

The mathematical expressions above apply over the surface of the ellipsoid. The cases below considers Earth's topography, above or below a reference ellipsoid. As such, they are topographical geocentric distances, Rt, which depends not only on latitude. See more

In astronomy, the International Astronomical Union denotes the nominal equatorial Earth radius as $${\displaystyle {\mathcal {R}}_{e\mathrm {E} }^{\mathrm {N} }}$$, … See more

The following radii are derived from the World Geodetic System 1984 (WGS-84) reference ellipsoid. It is an idealized surface, and the … See more

Geocentric radius
The geocentric radius is the distance from the Earth's center to a point on the spheroid surface at See more

The Earth can be modeled as a sphere in many ways. This section describes the common ways. The various radii derived here use the notation and dimensions noted above for the Earth as derived from the WGS-84 ellipsoid; namely,
Equatorial radius: a … See more

Earth's diameter is simply twice Earth's radius; for example, equatorial diameter (2a) and polar diameter (2b). For the WGS84 ellipsoid, that's respectively:
• 2a … See more