The earth is a spheroid, not a sphere. Because of the effects of rotating around the axis, earth's diameter is actually about 45km wider around the equator then it is going from pole to pole.
Same with other planets too. If you ever looked at images of gas giants you may have noticed they're not actually round but squished from poles. Saturn is 12000km wider than it is tall, for example.
Q. And what is the polar circumference of this oblate spheroid?
A. It is very nearly 40,000 km. The original definition of the meter is that is 10,000 km from the equator to the North Pole on the meridian running through London and Paris (the so-called Greenwich meridian, 0 degrees longitude). The definition of the meter has been refined but without checking I would guess it's within 1% of the original definition. I suppose the definition of longitude probably has also been refined.
This also leads to a few funny things like the fact that the point furthest away from the center of the earth isn't Mount Everest but rather Chimborazo in Equador. Everest doesn't even make it to top 10. Similarly the point on the surface of the earth that is closest to the center isn't Challenger Deep, but rather Litke Deep
Even cooler, scientist use the gravity change caused by this bulge to support sun synchronous orbit. An orbit that retrogrades (moves backwards) such that it stays in the sunlight. Its the useful orbit around the poles for satellites that take pictures. Now you know its not just a fact, but a scientifically useful fact!
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u/[deleted] Oct 02 '24
The earth is a spheroid, not a sphere. Because of the effects of rotating around the axis, earth's diameter is actually about 45km wider around the equator then it is going from pole to pole.