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Earth radius (denoted as R π¨ 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).
For planet Earth, which can be approximated as an oblate spheroid with radii 6 378.1 km and 6 356.8 km, the mean radius is = (( ) ) / = .The equatorial and polar radii of a planet are often denoted and , respectively.
The Earth is only approximately spherical, so no single value serves as its natural radius. Distances from points on the surface to the center range from 6,353 km (3,948 mi) to 6,384 km (3,967 mi). Several different ways of modeling the Earth as a sphere each yield a mean radius of 6,371 km (3,959 mi).
The Hill sphere, or the sphere of gravitational influence, of Earth is about 1.5 million km (930,000 mi) in radius. [163] [n 11] This is the maximum distance at which Earth's gravitational influence is stronger than that of the more distant Sun and planets.
The gravity gβ² at depth d is given by gβ² = g(1 β d/R) where g is acceleration due to gravity on the surface of the Earth, d is depth and R is the radius of the Earth. If the density decreased linearly with increasing radius from a density Ο 0 at the center to Ο 1 at the surface, then Ο(r) = Ο 0 β (Ο 0 β Ο 1) r / R, and the ...
Average distance from Earth (which the Apollo missions took about 3 days to travel) β Solar radius: 0.005 β 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) β Light-minute: 0.12 β Distance light travels in one minute β Mercury: 0.39 β Average distance from the ...
These proportionalities may be expressed by the formula: where g is the surface gravity of an object, expressed as a multiple of the Earth's, m is its mass, expressed as a multiple of the Earth's mass (5.976 Γ 10 24 kg) and r its radius, expressed as a multiple of the Earth's (mean) radius (6,371 km). [9]
The distance along the great circle will then be s 12 = RΟ 12, where R is the assumed radius of the Earth and Ο 12 is expressed in radians. Using the mean Earth radius, R = R 1 β 6,371 km (3,959 mi) yields results for the distance s 12 which are within 1% of the geodesic length for the WGS84 ellipsoid; see Geodesics on an ellipsoid for details.