I always thought a preferred higher order model of the Earth considered its shape relative to an oblate spheroid to tend very slightly towards a pear shape in a section through the poles, and to tend very slightly towards a rounded pentagon in a section through the equator.
The Earth was thought to be pear-shaped based on initial satellite measurements, but those measurements could only get the average shape as a function of latitude, not any longitudinal variations. Later measurements found that the next spherical harmonic was the one that was sort of a rounded regular tetrahedron, with one of it’s points at a (the North?) pole. If you imagine spinning that and taking the average, you can see where it would be pear shaped.
User R M Mentock, who I haven’t seen here for years, worked in the field, and linked to a description of that that he had written.
I read once that the surface of the Earth was smoother than a billiard ball by several powers of ten. So I’d call that a goddamned sphere, not an oblate sphereoid. If my source was wrong on that, then I dunno.
If the earth was a billiard ball, its surface would be allowed to vary by about 50 km (IIRC) to meet its smoothness spec. The difference between the highest point on earth (Mt. Everest) and the lowest point (Marianas trench) is only about 20 km. So it is well within spec for a billiard ball, but not by “several powers of ten.”
(I also already mentioned the billiard ball comparison in post #12 above)
sorry. I skimmed and didn’t think I saw anyone mention what I wanted to add.
Hey, dudes, could you comment on and, perhaps, excerpt here, portions of the argument vis-vis Wiki (which is not so important) but for the SD, posted two years ago in Is the Earth Like a Billiard Ball or Not?
It seems to be on the level.
Nope, it’s called a prolate spheroid. Take a tennis ball in one hand and squeeze the sides, allowing the “poles” to bulge out above and below your fist. If instead, you hold the ball on your palm and squeeze down with your other palm, letting the “equator” bulge out, that’s an oblate spheroid.