As it now widely dicussed and accepted that Earth is not a 'perfectly round sphere/ball but more a 'oblate spheroid' why then do NASA have 'photographs' of a ROUND Earth?
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$\begingroup$ The Earth is round. But, as widely discussed, it isn't perfectly round. $\endgroup$– Solomon SlowCommented Mar 17 at 1:54
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$\begingroup$ Possible duplicates: physics.stackexchange.com/q/8074/2451 , physics.stackexchange.com/q/26297/2451 , physics.stackexchange.com/q/107584/2451 and links therein. $\endgroup$– Qmechanic ♦Commented Mar 17 at 3:14
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1$\begingroup$ The polar diameter is 7,899.8km. The equatorial diameter is 7,926.4km. The 0.3% difference is not going to be visible in any depiction, photographic or otherwise. $\endgroup$– Ryan CavanaughCommented Mar 17 at 5:11
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$\begingroup$ hermiene.net/essays-trans/relativity_of_wrong.html $\endgroup$– John DotyCommented Mar 17 at 11:28
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4 Answers
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Yes, Earth does take the shape of an oblate spheroid, but only to a very marginal extent, such that it is barely noticeable.
If you are looking for a planet that more obviously takes the shape of an oblate spheriod, you should be looking at Saturn:
Unlike Earth, Saturn is made of of Hydrogen and Helium, and spins considerably faster. A day on Saturn lasts only 10.7 hours. Saturn's own gravity is not enough to maintain a perfectly spherical shape, and this has caused Saturn to bulge outwards at its equator.
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An oblate spheroid does not need to be very oblate to qualify as oblate. This one is not. It's that simple.
The shape of the Earth is, of course, considerably more complex than any idealized shape, be it round or oblate spheroid. More detailed information can be found on Wikipedia's page on the figure of the earth. What model is used depends on the accuracy required.
answered Mar 17 at 2:00
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Well the truth is that NASA doesn't have pictures of around Earth. However, your point is well taken in that the pictures certainly look like they show a round Earth. Even though the Earth is indeed an "oblate spheroid" it is not extremely oblate, for example, the polar radius (the distance from the center to one of the poles) is something like 3,950 miles while the equatorial radius (distance from the center to the equator) is some 3,963 miles. This is a difference of about 13 miles, given the size of the Earth, this is not a great deal of flattening, thus it is not surprising that the oblateness is not immediately obvious to the eye.
answered Mar 17 at 2:04
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The shape of the earth is called the geoid. An ellipsoid is just an approximation, and the geoid deviates from the reference ellipsoid by up to 106 m.
A sphere is, in turn, an approximation to the reference ellipsoid. The ellipsoid deviates from the sphere by up to 14 km.
While 14 km is much bigger than 106 m, it is still only about 1 tenth of 1 percent of the average diameter. So a picture will not visibly deviate from spherical shape.
