Radius For Spherical Earth
See also: Earth radiusThe shape of the Earth closely resembles a flattened sphere (a spheroid) with equatorial radius of 6,378.137 km; distance from the center of the spheroid to each pole is 6356.752 km. When calculating the length of a short north-south line at the equator, the sphere that best approximates that part of the spheroid has a radius of, or 6,335.439 km, while the spheroid at the poles is best approximated by a sphere of radius, or 6,399.594 km, a 1% difference. So as long as we're assuming a spherical Earth, any single formula for distance on the Earth is only guaranteed correct within 0.5% (though we can do better if our formula is only intended to apply to a limited area). McCaw recommends using the mean radius for a spherical approximation of the figure of the Earth, i.e., approximately 6371.01 km.
Read more about this topic: Great-circle Distance
Famous quotes containing the word earth:
“There is on the earth no institution which Friendship has established; it is not taught by any religion; no scripture contains its maxims. It has no temple, nor even a solitary column. There goes a rumor that the earth is inhabited, but the shipwrecked mariner has not seen a footprint on the shore. The hunter has found only fragments of pottery and the monuments of inhabitants.”
—Henry David Thoreau (1817–1862)