<p>The form of the <a href="http://en.wikipedia.org/wiki/Earth" rel="nofollow">Earth</a> is a approximately (to a very good approximation) an <a href="http://en.wikipedia.org/wiki/Oblate_spheroid" rel="nofollow">oblate spheroid</a> (difference between the polar diameter and equatorial diameter is ~20km which is ~1/300 of the mean diameter). The shape is distorted by tides (both in the solid body as well as the sea) and by topography. Topographical variation is about +10 to -10km (height of <a href="http://en.wikipedia.org/wiki/Mount_Everest" rel="nofollow">Everest</a> to depth of the <a href="http://en.wikipedia.org/wiki/Challenger_Deep" rel="nofollow">Challenger Deep</a>).</p>

<p>Up and down are defined by the local gravity vector, which to a good approximation is pointing into the Earth towards its centre. Hence wherever the sun is, down is into the Earth's surface (in the direction colloquially know as down)</p>

CC BY-SA 3.0
2015-01-30T17:26:30.993Z
2015-01-30T17:26:30.993Z
Conrad Turner
<p>As noted by Conrad Turner, the approximate shape of the Earth is an oblate spheroid, though it is so close to spherical that you would be pretty hard-pressed to see the difference without precise scientific equipment. <a href="http://blogs.discovermagazine.com/badastronomy/2008/09/08/ten-things-you-dont-know-about-the-earth/#.VMu8tysa6VM" rel="nofollow">This web page</a> has some pretty good information on this topic that you might be interested in.</p>

<p>When we talk about this shape, we are generally speaking of the land and sea. Gas in general has the property of not only having fluid shape, like a liquid, but also having indefinite volume. Gas expands to fill the container it is in. The atmosphere is not contained per se. What keeps it from simply expanding all the way out to the moon is Earth's gravity. But this means that faster moving air particles get further away from the surface than slower ones before being pulled back by gravity. So where exactly is the edge of the atmosphere? The outer-most layer of the atmosphere, <a href="http://en.wikipedia.org/wiki/Ionosphere" rel="nofollow">the ionosphere</a>, is very thin, and the further out toward space you go, the thinner it is. Where exactly its edge is, and what shape it has is... <a href="http://iopscience.iop.org/0370-1301/68/8/302/pdf/0370-1301_68_8_302.pdf" rel="nofollow">complicated</a>. Anyone who wants to make any authoritative statement on the shape or height of the edge of our atmosphere will have a few other authoritative statements to argue against.</p>

<p>While the exact shape of the atmosphere is difficult to define, it's pretty safe to say that it is not <em>exactly</em> spherical due mostly to the planet's rotation, and solar winds. The Earth's surface is also not <em>exactly</em> spherical due mostly to the planet's rotation, and tidal forces. Even if the entire surface was covered in water, rotation would flatten the planet's shape ever so slightly. And even if our rotation became tidally locked with the sun, and the moon... um... went away somehow, the tidal forces of the sun, would distort the spherical perfection ever so slightly. But laying all of that aside, the Earth is still probably closer to a sphere than most ball-shaped objects you have ever handled, whether you measure the "edge" of the atmosphere, the land and sea, or whatever.</p>

CC BY-SA 3.0
2015-01-30T18:15:24.367Z
2015-01-30T18:15:24.367Z
Mark Bailey
<p>I know earth is spherical in shape.</p>

<p>Does this means earths atmosphere is spherical in shape or the ground/(land+water combined) is in spherical shape.</p>

<p>I have some doubts if the second is true.</p>

<ol>
<li>since the earth is rotating around itself and  revolving around sun in the same time. When we see sun in the afternoon on top of your head. it can be actually you are upside down looking onto sun which is under you.</li>
</ol>

<p>I'll add my other doubts once some one answers my question.</p>

CC BY-SA 3.0
2015-01-30T13:57:28.340Z
It really isn't clear to me what your question is? The earth is not *exactly* spherical.
ProfRob
CC BY-SA 3.0
2015-01-30T18:23:14.940Z
How is the relative direction of "down" relevant to the shape of the Earth? This seems like an entirely separate question.
Mark Bailey
CC BY-SA 3.0
2015-02-01T04:50:15.623Z
This question does not appear to be about astronomy, within the scope defined in the [help]. It would be eligible for migration to [earthscience.se] if you [edit] to clarify what you mean and limit it to a single question at a time. See our [Ask] for more information and please don't cross-post on multiple [se] sites. Thanks!
TildalWave
CC BY-SA 3.0
2015-02-01T04:58:13.700Z
Food for thought; while the Earth isn't an exact sphere nor are its surface topography and the tidal bulge exactly smooth, [it is actually rounder than a billiard ball](http://www.universetoday.com/25893/is-the-earth-round/).
TildalWave
<orbit><the-sun><gravity><earth>
earth is spherical , does it mean the ground on earth is like a ball?
Strikers
# earth is spherical , does it mean the ground on earth is like a ball?

(Asked by: username_0 on 2015-01-30)

I know earth is spherical in shape.

Does this means earths atmosphere is spherical in shape or the ground/(land+water combined) is in spherical shape.

I have some doubts if the second is true.

1. since the earth is rotating around itself and revolving around sun in the same time. When we see sun in the afternoon on top of your head. it can be actually you are upside down looking onto sun which is under you.

I'll add my other doubts once some one answers my question.

**Tags:** orbit, the-sun, gravity, earth

> **Comments:**
> **username_1**: It really isn't clear to me what your question is? The earth is not *exactly* spherical.  
> **username_2**: How is the relative direction of "down" relevant to the shape of the Earth? This seems like an entirely separate question.  
> **username_3**: This question does not appear to be about astronomy, within the scope defined in the [help]. It would be eligible for migration to [earthscience.se] if you [edit] to clarify what you mean and limit it to a single question at a time. See our [Ask] for more information and please don't cross-post on multiple [se] sites. Thanks!  
> **username_3**: Food for thought; while the Earth isn't an exact sphere nor are its surface topography and the tidal bulge exactly smooth, [it is actually rounder than a billiard ball](http://www.universetoday.com/25893/is-the-earth-round/).  

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## 2 answers

### Answer by username_4 on 2015-01-30. Score: 3

The form of the [Earth](http://en.wikipedia.org/wiki/Earth) is a approximately (to a very good approximation) an [oblate spheroid](http://en.wikipedia.org/wiki/Oblate_spheroid) (difference between the polar diameter and equatorial diameter is ~20km which is ~1/300 of the mean diameter). The shape is distorted by tides (both in the solid body as well as the sea) and by topography. Topographical variation is about +10 to -10km (height of [Everest](http://en.wikipedia.org/wiki/Mount_Everest) to depth of the [Challenger Deep](http://en.wikipedia.org/wiki/Challenger_Deep)).

Up and down are defined by the local gravity vector, which to a good approximation is pointing into the Earth towards its centre. Hence wherever the sun is, down is into the Earth's surface (in the direction colloquially know as down)


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### Answer by username_2 on 2015-01-30. Score: 1

As noted by username_4, the approximate shape of the Earth is an oblate spheroid, though it is so close to spherical that you would be pretty hard-pressed to see the difference without precise scientific equipment. [This web page](http://blogs.discovermagazine.com/badastronomy/2008/09/08/ten-things-you-dont-know-about-the-earth/#.VMu8tysa6VM) has some pretty good information on this topic that you might be interested in.

When we talk about this shape, we are generally speaking of the land and sea. Gas in general has the property of not only having fluid shape, like a liquid, but also having indefinite volume. Gas expands to fill the container it is in. The atmosphere is not contained per se. What keeps it from simply expanding all the way out to the moon is Earth's gravity. But this means that faster moving air particles get further away from the surface than slower ones before being pulled back by gravity. So where exactly is the edge of the atmosphere? The outer-most layer of the atmosphere, [the ionosphere](http://en.wikipedia.org/wiki/Ionosphere), is very thin, and the further out toward space you go, the thinner it is. Where exactly its edge is, and what shape it has is... [complicated](http://iopscience.iop.org/0370-1301/68/8/302/pdf/0370-1301_68_8_302.pdf). Anyone who wants to make any authoritative statement on the shape or height of the edge of our atmosphere will have a few other authoritative statements to argue against.

While the exact shape of the atmosphere is difficult to define, it's pretty safe to say that it is not *exactly* spherical due mostly to the planet's rotation, and solar winds. The Earth's surface is also not *exactly* spherical due mostly to the planet's rotation, and tidal forces. Even if the entire surface was covered in water, rotation would flatten the planet's shape ever so slightly. And even if our rotation became tidally locked with the sun, and the moon... um... went away somehow, the tidal forces of the sun, would distort the spherical perfection ever so slightly. But laying all of that aside, the Earth is still probably closer to a sphere than most ball-shaped objects you have ever handled, whether you measure the "edge" of the atmosphere, the land and sea, or whatever.


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