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Earth radius (denoted as R 🜨 or R E) 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 (an oblate ellipsoid), the radius ranges from a maximum (equatorial radius, denoted a) of nearly 6,378 km (3,963 mi) to a minimum (polar radius, denoted b) of nearly 6,357 km (3,950 mi).
The Earth's radius is the distance from Earth's center to its surface, about 6,371 km (3,959 mi). While "radius" normally is a characteristic of perfect spheres, the Earth deviates from spherical by only a third of a percent, sufficiently close to treat it as a sphere in many contexts and justifying the term "the radius of the Earth".
[87] [88] Earth's shape also has local topographic variations; the largest local variations, like the Mariana Trench (10,925 metres or 35,843 feet below local sea level), [89] shortens Earth's average radius by 0.17% and Mount Everest (8,848 metres or 29,029 feet above local sea level) lengthens it by 0.14%.
Posidonius calculated the Earth's circumference by reference to the position of the star Canopus.As explained by Cleomedes, Posidonius observed Canopus on but never above the horizon at Rhodes, while at Alexandria he saw it ascend as far as 7 + 1 ⁄ 2 degrees above the horizon (the meridian arc between the latitude of the two locales is actually 5 degrees 14 minutes).
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The flattening of the earth was estimated at 1/294.26 and the earth's equatorial radius was estimated at 6378360.7 metres. [ 116 ] In the early 19th century, the Paris meridian's arc was recalculated with greater precision between Shetland and the Balearic Islands by the French astronomers François Arago and Jean-Baptiste Biot .
The square root appearing above can be eliminated for such applications as ordering locations by distance in a database query. On the other hand, some methods for computing nearest neighbors, such as the vantage-point tree , require that the distance metric obey the triangle inequality , in which case the square root must be retained.
Average distance from Earth (which the Apollo missions took about 3 days to travel) — Solar radius: 0.005 — Radius of the Sun (695 500 km, 432 450 mi, a hundred times the radius of Earth or ten times the average radius of Jupiter) — Light-minute: 0.12 — Distance light travels in one minute — Mercury: 0.39 — Average distance from the ...