Earth radius | |
---|---|
General information | |
Unit system | astronomy, geophysics |
Unit of | distance |
Symbol | , , |
Conversions | |
1 in ... | ... is equal to ... |
SI base unit | 6.3781×106 m[1] |
Metric system | 6,357 to 6,378 km |
English units | 3,950 to 3,963 mi |
Geodesy |
---|
Earth radius (denoted as R🜨 or RE) is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid, the radius ranges from a maximum of nearly 6,378 km (3,963 mi) (equatorial radius, denoted a) to a minimum of nearly 6,357 km (3,950 mi) (polar radius, denoted b).
A globally-average value is usually considered to be 6,371 kilometres (3,959 mi) with a 0.3% variability (±10 km) for the following reasons. The International Union of Geodesy and Geophysics (IUGG) provides three reference values: the mean radius (R1) of three radii measured at two equator points and a pole; the authalic radius, which is the radius of a sphere with the same surface area (R2); and the volumetric radius, which is the radius of a sphere having the same volume as the ellipsoid (R3).[2] All three values are about 6,371 kilometres (3,959 mi).
Other ways to define and measure the Earth's radius involve the radius of curvature. A few definitions yield values outside the range between the polar radius and equatorial radius because they include local or geoidal topography or because they depend on abstract geometrical considerations.
A nominal Earth radius (denoted ) is sometimes used as a unit of measurement in astronomy and geophysics, a conversion factor used when expressing planetary properties as multiples or fractions of a constant terrestrial radius; if the choice between equatorial or polar radii is not explicit, the equatorial radius is to be assumed, as recommended by the International Astronomical Union (IAU).[1]
Moritz
was invoked but never defined (see the help page).© MMXXIII Rich X Search. We shall prevail. All rights reserved. Rich X Search