The shape of the Earth has intrigued scientists throughout history. The general acceptance of the fact that the Earth is round came about in the first century A.D., although Pythagoras had already postulated a spherical Earth 600 years earlier.
The flat Earth concept resurfaced now and again in the Middle Ages, sometimes on religous grounds, but it is safe to say that mankind has known for 2000 years that we live on a sphere.
We know also that it is not a perfect sphere: the diameter from pole to pole is shorter than the diameter at the equator. The difference is small: the equatorial diameter is about 12,700 kilometers, and the pole to pole diameter is only about 40 km shorter.
Overall, though, the Earth tends to bulge at the equator and be squished at the poles because it is spinning around (yes…once every day). Folks near the equator are actually screaming west to east at just over 1,000 miles per hour. In effect, the datum represents the shape of the earth, or the surface of the earth at "zero elevation."
The flat Earth concept resurfaced now and again in the Middle Ages, sometimes on religous grounds, but it is safe to say that mankind has known for 2000 years that we live on a sphere.
We know also that it is not a perfect sphere: the diameter from pole to pole is shorter than the diameter at the equator. The difference is small: the equatorial diameter is about 12,700 kilometers, and the pole to pole diameter is only about 40 km shorter.
Overall, though, the Earth tends to bulge at the equator and be squished at the poles because it is spinning around (yes…once every day). Folks near the equator are actually screaming west to east at just over 1,000 miles per hour. In effect, the datum represents the shape of the earth, or the surface of the earth at "zero elevation."
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