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Line 12: The rotation of the earth also affects the [[sea level]], the imaginary surface that is used to measure [[altitude]]s from. This surface coincides with the mean water surface level in oceans, and is extrapolated over land by taking into account the local [[gravity of Earth\|gravitational potential]] and the centrifugal force. The difference of the [[radius\|radii]] is thus about 21 km. An observer standing at sea level on either [[geographical pole\|pole]], therefore, is 21 km closer to Earth's center than if standing at sea level on the Equator. As a result, the highest point on Earth, measured from the center and outwards, is the peak of Mount [[Chimborazo]] in [[Ecuador]] rather than [[Mount Everest]]. But since the ocean also bulges, like Earth and [[atmosphere of Earth\|its atmosphere]], Chimborazo is not as high above sea level as Everest is. Similarly the lowest point on Earth, measured from the center and outwards, is the [[Litke Deep]] in [[Arctic Ocean]] rather than [[Challenger Deep]] in [[Pacific Ocean]]. But since the ocean also flattens, like Earth and [[atmosphere of Earth\|its atmosphere]], Litke Deep is not as low below sea level as Challenger Deep is. More precisely, the surface of the Earth is usually approximated by an ideal [[oblate ellipsoid]], for the purposes of defining precisely the [[latitude]] and [[longitude]] grid for [[cartography]], as well as the "center of the Earth". In the [[World Geodetic System\|WGS-84]] standard [[Earth ellipsoid]], widely used for map-making and the [[GPS]] system, the radius of the Earth is assumed to be {{cvt\|6378.137\|km\|mi\|comma=gaps}} at the equator and {{cvt\|6356.7523142\|km\|mi\|comma=gaps}} center-to-pole; meaning a difference of {{cvt\|21.3846858\|km\|mi\|comma=gaps}} in the radii and {{cvt\|42.7693716\|km\|mi\|comma=gaps}} in the diameters, and a relative [[flattening]] of 1/298.257223563. The sea level surface is much closer to this standard ellipsoid than the surface of the solid Earth is.

Equatorial bulge: Difference between revisions