Earth radius of curvature | Wikipedia audio article
Channel: wikipedia tts
Date: 2019-06-15

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Earth_radius


00:01:40 1 Introduction
00:04:05 1.1 Physics of Earth's deformation
00:06:05 1.2 Radius and local conditions
00:07:40 2 Fixed radius
00:08:58 2.1 Equatorial radius
00:09:29 2.2 Polar radius
00:09:55 3 Location-dependent radii
00:10:06 3.1 Geocentric radius
00:11:18 3.1.1 Geophysical extremes
00:11:50 3.2 Radii of curvature
00:11:59 3.2.1 Principal sections
00:12:15 3.2.1.1 Meridional
00:13:11 3.2.1.2 Prime vertical
00:14:30 3.2.2 Directional
00:14:37 3.2.3 Combinations
00:15:30 4 Global average radii
00:17:25 4.1 Mean radius
00:18:00 4.2 Authalic radius
00:18:20 4.3 Volumetric radius
00:19:51 4.4 Rectifying radius
00:20:11 4.5 Mean curvature
00:22:33 4.6 Average distance from center to surface
00:23:25 5 Osculating sphere
00:26:51 6 Published values
00:28:32 7 History
00:29:19 8 See also
00:30:04 9 Notes
00:30:19 10 References
00:31:14 11 External links



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SUMMARY
=======
Earth radius is the distance from the center of Earth to a point on its surface. Its value ranges from 6,378 kilometres (3,963 miles) at the equator to 6,357 kilometres (3,950 miles) at a pole.
Earth's radius can be defined in different ways because Earth is not a perfect sphere. The surface to which a radius extends is commonly chosen to be on an ellipsoid representing the shape of Earth. Like the surface, what point gets used for the center of Earth is also a matter of definition and therefore contributes to the diverse ways of defining Earth's radius.
When only one radius is stated, the International Astronomical Union (IAU) prefers that it be the equatorial radius. The International Union of Geodesy and Geophysics (IUGG) gives three global average radii: the arithmetic mean of the radii of the ellipsoid (R1); the authalic radius, which is of a sphere having the same surface area as the ellipsoid (R2); and the volumetric radius, which is of a sphere having the same volume as the ellipsoid (R3). All three of those radii are about 6,371 kilometres (3,959 mi).
Many other ways to define Earth radius have been described. Some appear below. A few definitions yield values outside the range between polar radius and equatorial radius because they include local or geoidal topology or because they depend on abstract geometrical considerations.