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The Shape of the Moon

It's not what you think.

Stephen Green


August 3, 2014 - 10:00 am


From the Register:

A paper published in the July 30 issue of Nature by Ian Garrick-Bethell – an assistant professor of Earth and planetary sciences at University of California Santa Cruz – examines the shape of the Moon as it would be had not millions of meteorite collisions knocked chunks off it, and ponders how it got that way.

“If you imagine spinning a water balloon, it will start to flatten at the poles and bulge at the equator,” Garrick-Bethell said. “On top of that you have tides due to the gravitational pull of the Earth, and that creates sort of a lemon shape with the long axis of the lemon pointing at the Earth.”

The Moon formed about four billion years ago and was initially much closer to Earth, and spinning rather more than it does today. As the Moon cooled and hardened, the effects of tidal forces exerted by Earth froze the surface into a slightly elongated shape with a bulge pointing towards Earth and a corresponding bump on the other side.

I think she’s just as rotational and spherical as she was at two billion.


Cross-posted from Vodkapundit

Stephen Green began blogging at in early 2002, and has served as PJMedia's Denver editor since 2008. He's one of the hosts on PJTV, and one-third of PJTV's Trifecta team with Scott Ott and Bill Whittle. Steve lives with his wife and sons in the hills and woods of Monument, Colorado, where he enjoys the occasional lovely adult beverage.

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All Comments   (4)
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You look great in that, a married man quickly answers.
29 weeks ago
29 weeks ago Link To Comment
Meh, nothing new -- Back in the 1960s and early 70s, Gulf Oil used to sponsor NBC's coverage of the Gemini and Apollo space launches, which opened up with an image of the Earth transitioning into the Gulf logo. But at that time the hot new theory was the Earth was the celestial body that was lopsided, and it was popular enough back then for Gulf and NBC to actually change the logo to something that looked an egg-shaped home planet that transitioned into the sponsor's symbol. The 'cutting edge' design didn't go over very well with the viewers, apparently, since after showing up on a couple of launch coverages, they went back to the rounded Earth image.
29 weeks ago
29 weeks ago Link To Comment
Yup, nothing new here.

There is no such thing as a perfect sphere in the Solar System. Whether it is rotational or tidal, there is always a bulge; and other irregularities in any body that has a solid crust. (That is among the bodies that have enough mass to try to assume a spherical shape.)

It is invisible to the eye, though, on just about everything. You can just barely see it in very good pictures of Jupiter, with its mostly gaseous makeup and fast rotation (but only at the Jovian solstice, when both poles are equally illuminated - otherwise that throws it off).
29 weeks ago
29 weeks ago Link To Comment
Sure, and there's no such thing as an elliptical orbit either. Still, an ellipse is the closest conical section to most orbits. Finally, to all those who continue to say that a cannonball fired from a cannon follows a parabolic trajectory ... nope, that's wrong. The closest conical section is an ellipse, so stop telling people that a cannonball follows a parabolic trajectory. It would in a uniform gravitational field , but another one of those "no such thing"s is a uniform gravitational field. It also would if fired at exactly escape velocity in a two body, point mass approximation, but there's no such cannon ball.
29 weeks ago
29 weeks ago Link To Comment
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