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:
“Some of us still get all weepy when we think about the Gaia Hypothesis, the idea that earth is a big furry goddess-creature who resembles everybody’s mom in that she knows what’s best for us. But if you look at the historical record—Krakatoa, Mt. Vesuvius, Hurricane Charley, poison ivy, and so forth down the ages—you have to ask yourself: Whose side is she on, anyway?”
—Barbara Ehrenreich (b. 1941)