# The Earth is not a sphere; but is the Earth's atmosphere a sphere? **URL:** \ **Category:** Factual Questions\ **Created:** [October 6, 2007, 8:06pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785 "2007-10-06T20:06:17Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Randy\_Seltzer](https://avatars.discourse-cdn.com/v4/letter/r/ee7513/32.png) [@Randy\_Seltzer](https://boards.straightdope.com/u/Randy_Seltzer)\ **Post date:** [October 6, 2007, 8:06pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/1 "2007-10-06T20:06:17Z")
The Earth is a little bit flattened at the poles (or conversely, a little bit bulged at the equator). But is the atmosphere also flattened at the poles? The atmosphere shouldn’t “care” about the shape of the Earth, should it? I mean, the atmosphere should end (for the purposes of this question, let’s say the atmosphere “ends” when atmospheric pressure becomes immesurably small) at the same distance from the center of the Earth, regardless of how much rock is underneath it. Right? If this were true, we’d see higher-than-expected air pressures at the poles, and my brief unscientific research seems to bear this out: The elevation at the South pole is roughly 2835 meters.[cite](http://en.wikipedia.org/wiki/South_Pole#Geography) The standard barometric pressure at that altitude is 548mmHg.[cite](http://www.altitude.org/calculators/airpressure.htm) The actual pressure at the South pole runs between 670-685.[cite](http://astro.uchicago.edu/cara/southpole.edu/weather2.html) {I’m totally prepared to be corrected on any of this. Including my math or the soundness or my reasoning.} So is it true? Is the Earth’s atmosphere much closer to a true sphere than the Earth itself? ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [October 6, 2007, 8:35pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/2 "2007-10-06T20:35:40Z")
Just a guess, but since the atmosphere spins more-or-less in synch with the earth, I would assume it bulges for the same reason. I would say centrifugal force, but some clown is certain to tell me it doesn’t exist (neither is there a gravitational force, in exactly the same way) so I will say that the air molecules above the equator are a bit more successful moving in a straight line than those at the poles. Actually, the prevailing winds slightly counterbalance this, but they don’t go 1000 mph as the earth’s surface at the equator nearly does. So it ought to bulge a bit less. ---
**Author:** ![Spatial\_Rift\_47](https://avatars.discourse-cdn.com/v4/letter/s/a8b319/32.png) [@Spatial\_Rift\_47](https://boards.straightdope.com/u/Spatial_Rift_47)\ **Post date:** [October 6, 2007, 9:28pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/3 "2007-10-06T21:28:57Z")
[QUOTE=Hari Seldon] Just a guess, but since the atmosphere spins more-or-less in synch with the earth, I would assume it bulges for the same reason. I would say centrifugal force, but some clown is certain to tell me it doesn’t exist (neither is there a gravitational force, in exactly the same way) so I will say that the air molecules above the equator are a bit more successful moving in a straight line than those at the poles. [/QUOTE] Centrifugal force exists, but only in the rotating reference frame. Its counterpart, centripetal force, exists in the stationary or “lab” frame. The gravitational force most definitely exists in all reference frames, even if some of them aren’t experiencing it at certain moments. Dunno about the atmosphere question though. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [October 6, 2007, 9:31pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/4 "2007-10-06T21:31:15Z")
[QUOTE=Spatial Rift 47] Centrifugal force exists, but only in the rotating reference frame. [/QUOTE] Dr. Brantley would be very angry with me if I didn’t say the following: > [@](#): > > There is no such thing as centrifugal force. It’s inertia. ---
**Author:** ![bouv](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@bouv](https://boards.straightdope.com/u/bouv)\ **Post date:** [October 6, 2007, 9:36pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/5 "2007-10-06T21:36:59Z")
IIRC, the Earth is the closest thing to a perfect sphere on Earth. The ratio of the long diameter at the equator to the short ones at the poles is small compared to lots of other objects we consider spheres, like balls, bubbles, etc… ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 6, 2007, 9:56pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/6 "2007-10-06T21:56:17Z")
The atmosphere takes its shape from the shape of the gravity well its in, not from the shape of the dirt ball in the middle of that gravity well. If Earth had much stronger gravity on one side than the other (say a small neutronium deposit) the atmosphere would react to that, even if the planet itself was perfectly spherical. So I’m gonna suggest that the shape of the “top” of the atmosphere matches roughly the shape of the gravity well, net of centrifugal/centripetal forces. Also net of electromagnetic forces on the ions created & moved by the solar wind. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [October 6, 2007, 10:59pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/7 "2007-10-06T22:59:17Z")
How are you defining the top of the atmosphere? ‘Immeasurably small’ doesn’t cut it. Do the radiation belts count as part of the atmosphere? ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [October 6, 2007, 11:23pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/8 "2007-10-06T23:23:29Z")
[QUOTE=bouv] the Earth is the closest thing to a perfect sphere on Earth. [/QUOTE] I don’t think so. This wiki page on [earth radius](http://en.wikipedia.org/wiki/Earth_radius) says the difference between poles and equator is just under 22km, for a variance of about 1 part in 300. Here’s a link to a place that sells [tungsten-carbide balls](http://www.smallparts.com/products/descriptions/btc.cfm) that are claimed to be spherical within 0.000025” - for a 1/2" ball, that’s one part in 20,000. ---
**Author:** ![Randy\_Seltzer](https://avatars.discourse-cdn.com/v4/letter/r/ee7513/32.png) [@Randy\_Seltzer](https://boards.straightdope.com/u/Randy_Seltzer)\ **Post date:** [October 6, 2007, 11:33pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/9 "2007-10-06T23:33:17Z")
[QUOTE=Quartz] How are you defining the top of the atmosphere? ‘Immeasurably small’ doesn’t cut it. Do the radiation belts count as part of the atmosphere? [/QUOTE] I think you understand my question. How, for the purposes of my question, would you define the “top of the atmosphere”? Do you really think the radiation belts qualify for the purposes of this question? Really? ---
**Author:** ![ChrisBooth12](https://avatars.discourse-cdn.com/v4/letter/c/e95f7d/32.png) [@ChrisBooth12](https://boards.straightdope.com/u/ChrisBooth12)\ **Post date:** [October 7, 2007, 6:09am UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/10 "2007-10-07T06:09:26Z")
[QUOTE=Xema] I don’t think so. This wiki page on [earth radius](http://en.wikipedia.org/wiki/Earth_radius) says the difference between poles and equator is just under 22km, for a variance of about 1 part in 300. Here’s a link to a place that sells [tungsten-carbide balls](http://www.smallparts.com/products/descriptions/btc.cfm) that are claimed to be spherical within 0.000025” - for a 1/2" ball, that’s one part in 20,000. [/QUOTE] IIRC the Earth is more of a sphere then the tolerance for billiard balls. ---
**Author:** ![Siam\_Sam](https://avatars.discourse-cdn.com/v4/letter/s/d78d45/32.png) [@Siam\_Sam](https://boards.straightdope.com/u/Siam_Sam)\ **Post date:** [October 7, 2007, 6:16am UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/11 "2007-10-07T06:16:29Z")
I’ve seen footage of experiments with flame aboard the space shuttles, and candle flame always looks spherical. Would the same forces or lack thereof involved in that make Earth’s atmosphere spherical? ---
**Author:** ![Robot\_Arm](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robot_arm/32/18280_2.png) [@Robot\_Arm](https://boards.straightdope.com/u/Robot_Arm)\ **Post date:** [October 7, 2007, 6:49am UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/12 "2007-10-07T06:49:27Z")
[QUOTE=LSLGuy] If Earth had much stronger gravity on one side than the other (say a small neutronium deposit) the atmosphere would react to that, even if the planet itself was perfectly spherical. [/QUOTE] The only way to have greater gravity on one side of the planet is to also have greater density. The Earth rotates around an axis that passes through its center of gravity. An unbalanced Earth would wobble like an unbalanced tire as it turned. I don’t know all the effects that would have, but I suspect that atmosphere density would be the least of our worries. ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [October 7, 2007, 7:58am UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/13 "2007-10-07T07:58:16Z")
Jeez a dozen posts and nobody has mentioned the obvious point? The atmosphere has tides. Aside from the pull of the moon and sun the atmosphere swells as it heats up and shrinks as it cools. That all causes the depth of the atmosphere to change constantly. So no, that atmopshere is certainly not spherical. ---
**Author:** ![Richard\_Pearse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/richard_pearse/32/13144_2.png) [@Richard\_Pearse](https://boards.straightdope.com/u/Richard_Pearse)\ **Post date:** [October 7, 2007, 10:31am UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/14 "2007-10-07T10:31:07Z")
Parts of the atmosphere certainly aren’t spherical. The troposhpere where most of the weather happens is much thicker at the equator copared to the poles. > [@](#): > > The actual pressure at the South pole runs between 670-685 Those figures are in mb not mmhg. They are equivalent to 502 - 514 mmhg. This would suggest the atmosphere is thinner at the poles. It should also be pointed out that the “standard atmosphere” has no particular bearing on reality, particularly when considering an extreme part of the Earth. Also from [Aerospaceweb.org | Ask Us - Height of the Atmosphere](http://www.aerospaceweb.org/question/atmosphere/q0090.shtml) > [@](#): > > Along the equator, the atmosphere tends to bulge outward more so than at the poles due to the centrifugal effect of the planet’s rotation as well as the gravitational attraction of the Moon. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [October 7, 2007, 10:40am UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/15 "2007-10-07T10:40:34Z")
[QUOTE=ChrisBooth12] IIRC the Earth is more of a sphere then the tolerance for billiard balls. [/QUOTE] [This site](http://hypertextbook.com/facts/2004/OluwoleOwoseni.shtml) says a typical billiard ball is 2.25" in diameter, with a tolerance of .005". That gives a variance of 1 part in 450, compared to 1 in 300 for the Earth. So the billard ball wins here. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [October 7, 2007, 11:52am UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/16 "2007-10-07T11:52:06Z")
This site on the [South Pole Station](http://www.antarcticconnection.com/antarctic/stations/southpole.shtml) says: > [@](#): > > The station is at an elevation of 9,300’ (2900m), however the equivalent pressure elevation, based on polar atmospheric conditions, will vary from 10,800(3300m) to 13,120 (4,000m). Which is another way of saying that the atmosphere is not as thick there. Another important point is weather: the atmosphere regularly develops bulges (high-pressure areas) and depressions (low-pressure areas). These make it non-spherical over areas spanning hundreds of miles. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [October 7, 2007, 12:47pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/17 "2007-10-07T12:47:18Z")
The usual bit about the earth being smoother than a billiard ball is talking about surface finish, not overal sphericity. The bumps on the Earth, from the-trench-which-shall-remain-nameless-and-I-HOPE-unvisited-in-a-future-post to the peak of Everest, represent a surface roughness of ~12 miles on a sphere of diameter ~8000 miles. Overall, that’s pretty smooth. But as others have pointed out, that ignores the fact that the ball might be real smooth, but it isn’t really all that round. ---
**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\ **Post date:** [October 7, 2007, 3:28pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/18 "2007-10-07T15:28:55Z")
[QUOTE=LSLGuy] The usual bit about the earth being smoother than a billiard ball is talking about surface finish, not overal sphericity. The bumps on the Earth, from the-trench-which-shall-remain-nameless-and-I-HOPE-unvisited-in-a-future-post to the peak of Everest, represent a surface roughness of ~12 miles on a sphere of diameter ~8000 miles. Overall, that’s pretty smooth. But as others have pointed out, that ignores the fact that the ball might be real smooth, but it isn’t really all that round. [/QUOTE] Yes, that’s correct. However (to continue the hijack), the surface finish of the Earth (12 parts in 8000) equates to a surface roughness on a pool ball of over 3 thousandths of an inch. That’s _extremely_ rough when you’re talking about a manufactured product. So, the upshot is: Sphericity: A pool ball is slightly more spherical that the Earth Surface Roughness: A pool ball is substantially smoother than the Earth. ---
**Author:** ![Randy\_Seltzer](https://avatars.discourse-cdn.com/v4/letter/r/ee7513/32.png) [@Randy\_Seltzer](https://boards.straightdope.com/u/Randy_Seltzer)\ **Post date:** [October 7, 2007, 4:54pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/19 "2007-10-07T16:54:15Z")
[QUOTE=1920s Style “Death Ray”] Those figures are in mb not mmhg. They are equivalent to 502 - 514 mmhg. This would suggest the atmosphere is thinner at the poles. It should also be pointed out that the “standard atmosphere” has no particular bearing on reality, particularly when considering an extreme part of the Earth. [/QUOTE] Gah! I knew I shouldn’t have attempted any reasoning. Especially anything involving math. ---
**Author:** ![Derleth](https://avatars.discourse-cdn.com/v4/letter/d/b9e5f3/32.png) [@Derleth](https://boards.straightdope.com/u/Derleth)\ **Post date:** [October 7, 2007, 7:23pm UTC](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785/20 "2007-10-07T19:23:45Z")
[QUOTE=Spatial Rift 47] Centrifugal force exists, but only in the rotating reference frame. [/QUOTE] [I refer you all to this xkcd strip.](http://xkcd.com/123/) [Next page](https://boards.straightdope.com/t/the-earth-is-not-a-sphere-but-is-the-earths-atmosphere-a-sphere/421785.md?page=2)