Earth's rotation, internal density variations, and external tidal forces cause its shape to deviate systematically from a perfect sphere. Local 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

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 … See more

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

The first published reference to the Earth's size appeared around 350 BC, when Aristotle reported in his book On the Heavens that mathematicians had guessed the circumference of the Earth to be 400,000 stadia. Scholars have interpreted Aristotle's … See more