Earth Radius
Because the Earth is not perfectly spherical, no single value serves as its natural radius. Distances from points on the surface to the center range from 6,353 km to 6,384 km (≈3,947–3,968 mi). Several different ways of modeling the Earth as a sphere each yield a mean radius of 6,371 km (≈3,959 mi).
While "radius" normally is a characteristic of perfect spheres, the term as employed in this article more generally means the distance from some "center" of the Earth to a point on the surface or on an idealized surface that models the Earth. It can also mean some kind of average of such distances, or of the radius of a sphere whose curvature matches the curvature of the ellipsoidal model of the Earth at a given point.
This article deals primarily with spherical and ellipsoidal models of the Earth. See Figure of the Earth for a more complete discussion of models.
The first scientific estimation of the radius of the earth was given by Eratosthenes.
Earth radius is also used as a unit of distance, especially in astronomy and geology. It is usually denoted by .
Read more about Earth Radius: Fixed Radii, Mean Radii
Famous quotes containing the word earth:
“What a dissimilarity we see in walking, swimming, and flying. And yet it is one and the same motion: it is just that the load- bearing capacity of the earth differs from that of the water, and that that of the water differs from that of the air! Thus we should also learn to fly as thinkers—and not imagine that we are thereby becoming idle dreamers!”
—Friedrich Nietzsche (1844–1900)