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Question
#39490. kristian88
asks:
What shape is the Earth?
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gmackematix
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Well, it is as close to being a sphere as a snooker ball. The flattening at the poles that makes it "oblate" is hardly noticeable and if the Earth were the size of a snooker ball, the dampness of the oceans and the difference between the top of Everest and the bottom of the Marianas trench would be barely discernable by the human fingertip.
Oct 04 03, 9:03 PM
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Dracophilly
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It's an omnisphere. more egg-shaped than truly spherical. :)
Oct 05 03, 8:44 AM
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sequoianoir
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omnisphere is not a word as far as it is not in any dictionary that I can find, and web references suggest little more with regards to it defining a shape. (especially since omni means "all" or "every")
The Earth is definitely not OVOID -ie. egg shaped (having a "pointy" end and a "fatter rounder" end).
It is an OBLATE SPHEROID
Due to its spinning, it is slightly wider by about 13 miles (22 km) on the radius (26 miles diameter) at the equator than from pole to pole.
A spheroid is almost a sphere.
"Oblate" means wider at the equator.
"Prolate" would be wider at the poles. (could happen to a moon experiencing a strong tidal force)
Gmack, I disagree that the Earth is as round as a snooker ball. The difference on the Earth is that the equatorial diameter is 0.33% more than the polar diameter. If snooker balls were this spherically "inaccurate" you wouldn't be able to play the game.
Also you could easily feel the difference between the "top of Everest" and "bottom of the Marianas trench", this being only just less than the thickness of a sheet of paper on a snooker ball.
Oct 05 03, 10:07 AM
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gmackematix
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0.33% would be a small fraction of a millimetre's difference between the diameters on a snooker ball. Surely "wouldn't be able to play the game" is a slight exaggeration and if we certainly wouldn't spot the oblateness with the naked eye. Mt Everest's peak is about 5 miles above sea level and the Marianas trench is only 8 miles. The difference is 13 miles. The extreme sensitivity of human fingers can detect 0.02 microns. Hmmm. OK, I'll agree with you on the second part!
Oct 05 03, 11:12 AM
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sequoianoir
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My "wouldn't be able to play the game" was meant to reflect the difficulty of making accurate shots with all the screw, side, top, draw etc with even bounce and regular rebound angles from cushions. Balls would rarely run in a straight line especially at slow speeds and when hitting another ball the contact angle could not be predicted. I think 2 balls with a 0.33% oblateness could have a random contact with a 2 degree variation. They may even "settle" like bowls do.
I'd like to see Davis, Hendry and co play with balls this far out of being truly round and see how they get on. I bet century breaks (even half centuries) would become impossible !
Oct 05 03, 12:07 PM
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