<blockquote>
<p>The picture above is an image of the Earth without water. We know that the picture above is a very exaggerated one.</p>
</blockquote>
<p><strong>About the image</strong></p>
<p>The image shown in the question is very widely claimed to show an image of the Earth without water. A google image search for that image comes up with the nice logo &quot;earth form without water&quot;. This image pops up on the internet again and again. This image does not show an Earth without water, even greatly exaggerated.</p>
<p>Note that the image in the question has a fuzzed out title and legend. All of the images on the internet that claim this is an image of the Earth without water have a fuzzed out title and legend. A non-spinning version of that image with the correct title and legend is below. (I do not like reading around animated gifs.)</p>
<p><a href="https://i.sstatic.net/m5eh9.png" rel="noreferrer"><img src="https://i.sstatic.net/m5eh9.png" alt="Exaggerated image of the Earth's geoid height, with legend" /></a>
<sup>Source: Bezděk, Aleš, and Josef Sebera. &quot;Matlab script for 3D visualizing geodata on a rotating globe.&quot; Computers &amp; Geosciences 56 (2013): 127-130.</sup></p>
<p>The above image is by the author of the image. The title says what the image shows, which is the geoid height. The legend shows that the variation from the highest to lowest geoid height is less than 200 meters. Compare that with the 19.777 km altitude difference between the highest mountain above sea level and the deepest trench below sea level. The image shows the Tibetan plateau as below the reference ellipsoid and shows the Java trench (not visible in the above) as above the reference ellipsoid. This is not a world without oceans.</p>
<p><strong>So what does the image show?</strong></p>
<p>What the image does show is the geoid height, greatly exaggerated. A geoid is the surface of constant gravitational plus centrifugal potential that is the best fit in a least squares sense to mean sea level. In other words, the geoid portrays the Earth's gravitational field. A simpler model of mean sea level is an oblate ellipsoid. The geoid height at some point is the altitude difference between corresponding points on the geoid and on the reference ellipsoid. Red areas in the image (positive geoid height) show where the geoid is above the reference ellipsoid while blue areas (negative geoid height) show where the geoid is below the reference ellipsoid.</p>
<p>Look at the Tibet Plateau in the rotating image. It is blue, which means the geoid there is below the reference ellipsoid. Look at the Java Trench. It is the very deepest red, which means the geoid there is above the reference ellipsoid. The Rocky Mountains are white, no different than the rest of the northern North America. The Alps are reddish, but not as red as is the eastern North Atlantic.</p>
<p>The Tibet Plateau shows up as a depression in this image instead of as a large elevated land mass because it is are very large blob of rock that has less than average density. The rock near the Java Trench is very dense basalt.</p>
<p>The image does not represent anything close to what many say it represents. The image does represent what the author intended it to represent. The image is interesting to those who know what the image portrays. The problem is that the image is so often described incorrectly.</p>
<p><strong>An image of the Earth without water</strong></p>
<p>An image of the Earth without water, slightly exaggerated, is shown below.</p>
<p><a href="https://i.sstatic.net/Mo0hC.jpg" rel="noreferrer"><img src="https://i.sstatic.net/Mo0hC.jpg" alt="An image of the Earth with all of it waters gathered into a ball about 1365 km across hovering over the western US" /></a>
<sup>Source: : Jack Cook, Woods Hole Oceanographic Institution, Howard Perlman, USGS, <a href="https://apod.nasa.gov/apod/ap120515.html" rel="noreferrer">Astronomy Picture of the Day 2012 May 15</a></sup></p>
<p>The Earth is round rather than lumpy. For portrayal purposes, a ball of water about 1365 km across hovers over the western US. That ball represents all of the Earth's surface waters.</p>
<br>
<p><strong>Comparison to a basketball</strong></p>
<p>The difference between the Earth's equatorial  and polar radii is about 21.385 km. The difference between the height of the highest mountain on the Earth above sea level and the Earth's deepest trench below sea level is about 19.777 km.</p>
<p>Shrinking these down to the size of a basketball with a circumference of 29.5 inches (I used US units because that is what NBA regulations specify) shrinks the 21.385 km difference between the equatorial and polar radii to a mere 0.4 millimeters, shrinks the height of Mount Everest above sea level to 0.165 millimeters, and shrinks the depth Challenger Deep below sea level to 0.204 millimeters.</p>
<p>A basketball is supposed to be round(ish). That the Earth's polar radius is 99.66% of its equatorial radius makes the Earth fairly &quot;roundish&quot;. The roundness of the Earth is in line with the roundness of a billiard ball, and probably for a basketball. (While I did find roundness requirements for a billiard ball, I was unsuccessful in finding roundness requirements for a basketball.)</p>
<p>What about smoothness? Basketballs are not smooth. They are intentionally designed with stipples (pebbles) and channels so as to make basketballs easier to handle. There are patents galore regarding the size, shape, and placement of those pebbles and channels. The pebbles are a bit higher than 0.17 millimeters and the channels are significantly deeper than 0.2 millimeters. The Earth is smoother than a basketball because basketballs are unsmooth by design.</p>

CC BY-SA 4.0
2020-08-17T09:00:13.627Z
@Emil - I added a comparison with a basketball. The image in the question is one that I do not like because of the way it misrepresents the Earth and the way it is misrepresented on the internet. Look at the Himalaya in that image. They are blue. Rather deep blue. The geoid is below mean sea level at the Himalaya. The deepest red (the highest) is in the ocean, offshore of Indonesia. There is a deep trench there, not as deep as the Marianas Trench, but still, it's deep.
David Hammen
CC BY-SA 4.0
2020-08-17T09:16:28.380Z
@pdh0710 - It is not your fault. It is the fault of the people who created that image, and even more so, it is fault of the many people who have incorrectly promulgated that image across the internet. No matter what exaggerations one applies, this is not how the Earth looks, with or without water.
David Hammen
CC BY-SA 4.0
2020-08-17T10:23:37.863Z
So interestingly, the Himalaya would have about the height of one of the basketball pebbles!
Peter - Reinstate Monica
CC BY-SA 4.0
2020-08-18T18:08:43.267Z
@Peter Much smaller.
Spencer
CC BY-SA 4.0
2020-08-18T18:08:52.477Z
Now your answer makes me want to know how Earth compares to the required roundness for billiard balls :)
jpa
CC BY-SA 4.0
2020-08-18T18:15:15.600Z
@jpa - IIIRC, Phil Plait ("the Bad Astronomer") compared the Earth to a billiard ball and wrote that the roundness of the Earth is well within spec, but that the smoothness was not. Those who have played pool in a bar or a pool hall know that when racking the balls, one has to rotate the balls on the corners of the rack just right so that they roll towards the other balls in order to result in a nice tight rack. If one doesn't do tha, there will be a few balls that move a lot the break and a cluster of balls that don't move much at all. The table isn't flat and the balls aren't quite round.
David Hammen
CC BY-SA 4.0
2020-08-18T22:11:10.820Z
@Spencer Himalaya is  8km/12700km = 6.3E-4 , and the basketball pebble is 0.17mm/238.8mm = 6.7E-4.
Peter - Reinstate Monica
CC BY-SA 4.0
2020-08-17T00:37:17.667Z
2020-08-20T04:35:09.073Z
2020-08-20T04:35:09.073Z
David Hammen
<p>The deviations of Earth from a sphere are of order 20 km. This approximates both the difference between equatorial and polar radii (defining an ellipsoid) and the difference between the highest and lowest points (Mount Everest and Mariana Trench) relative to the ellipsoid. A basketball is about 50 million times smaller than Earth, and the corresponding deviations on a basketball would be 0.4 mm.</p>
<p>The <a href="https://www.productplayoffs.com/best-indoor-basketball/" rel="noreferrer">depth</a> of the main grooves or &quot;ribs&quot; on a real basketball is about 2 mm. I am unable to find a source for the thickness of the numerous bumps or &quot;pebbles&quot; on a real basketball, but it is plausibly close to 0.4 mm. Thus, the bumps that cover the ball are somewhat to scale with the largest 20 km features of Earth, though of course Earth does not have such density of 20 km features.</p>

CC BY-SA 4.0
2020-08-17T09:09:05.003Z
I have found patents galore regarding basketballs. Patents on basketballs go back almost 100 years. The first one I found dates back to 1928. Yet very few recent basketball patents cite **any** prior art (what???).  Not a single one of those patents I read specified how deep the channels are or how large the pebbles are. I'm used to reading patents that give exquisite detail that would let me recreate the object in question if I had the requisite skills and equipment. That's not possible with the basketball patents I have read.
David Hammen
CC BY-SA 4.0
2020-08-17T09:28:02.583Z
BTW, welcome aboard the Astronomy Stack Exchange. Nice answer.
David Hammen
CC BY-SA 4.0
2020-08-17T13:01:55.953Z
And with the migration, welcome aboard the Earth Science StackExcange!
David Hammen
CC BY-SA 4.0
2020-08-17T07:45:54.460Z
2020-08-17T07:45:54.460Z
nanoman
<p>A basketball is a <em><strong>sphere</strong></em> while Earth is an <em><strong>oblate spheroid</strong></em>, meaning Earth's equatorial radius is larger than its polar radius (as mentioned already in <a href="https://earthscience.stackexchange.com/a/20078/18946">David Hammen's answer</a> and <a href="https://earthscience.stackexchange.com/a/20079/18946">nanoman's answer</a>, I have just introduced the <em>name</em> for this phenomenon).</p>
<p><strong>What exactly is an <a href="https://en.wikipedia.org/wiki/Spheroid" rel="nofollow noreferrer">oblate spheroid</a>?</strong></p>
<p>If you take an ellipse and rotate it around its major (longer) axis you get a prolate spheroid, much like an Australian football:</p>
<img src="https://i.sstatic.net/E0rG2.png" height="150">
<p>If you rotate the ellipse around its minor (shorter) axis, you get an oblate spheroid, more like a lentil, M&amp;M chocolate, or mandarin fruit:</p>
<p><img src="https://i.sstatic.net/j4qQI.png" height="200"><img src="https://i.sstatic.net/dFd4z.png" height="200"></p>
<p>Here are the oblate and prolate spheroids side-by-side:</p>
<img src="https://i.sstatic.net/3kjAS.png" width="500">
<p>This is a sphere:</p>
<p><img src="https://i.sstatic.net/v6YIr.png" width="250"><img src="https://i.sstatic.net/uIyrU.png" width="300">.</p>
<p><strong>Earth is an oblate spheroid, so a basketball is not the best model. A mandarin fruit is better.</strong></p>

CC BY-SA 4.0
2020-08-18T05:22:13.323Z
Yes, the Earth is an oblate spheroid, but barely. It's much closer to a perfect sphere than to a mandarin, which is visibly oblate.
CJ Dennis
CC BY-SA 4.0
2020-08-18T08:37:12.140Z
The mandarin in my picture is not so oblate.
user1271772
CC BY-SA 4.0
2020-08-18T09:02:14.603Z
I can see without measuring it that the mandarin is oblate. I can't see without measuring that the Earth is oblate. To the naked eye, the Earth looks perfectly spherical.
CJ Dennis
CC BY-SA 4.0
2020-08-18T09:37:16.560Z
The mandarin in your picture is visibly oblate. The Earth is not visibly oblate. A visibly oblate basketball would not pass referee inspection. The Earth shrunken to the size of a basketball most likely would pass inspection on the basis of roundness.
David Hammen
CC BY-SA 4.0
2020-08-18T21:08:35.203Z
I would think the basketball on the ground would be an oblate spheroid as well.  The Earth's oblateness is about 1/1000th it's diameter.  Basketballs are inflated to 8 psi and are made of somewhat stiff material, but the weight would tend to squish it just a little.  With a radius of 4.5 inches looking down the circular area would be about 64 square inches.  Very roughly 512 pounds of pressure tending to overcome gravity and keep it spherical.  However the weight of 22 ounces would tend to flatten it, making it oblate.  The ratio is 1/372, about 3 times the Earth's oblateness.
Jason Goemaat
CC BY-SA 4.0
2020-08-19T06:04:01.080Z
@JasonGoemaat And here I thought to recall that the Earth's oblateness was 1/298, so surprisingly close to your back-of-the-envelope oblateness of a basketball
Hagen von Eitzen
CC BY-SA 4.0
2020-08-19T14:18:12.443Z
@Hagen von Eitzen you're right, don't know what I was thinking....  Used the km difference in radius from another question and a misremembered diameter of the Earth
Jason Goemaat
CC BY-SA 4.0
2020-08-18T00:13:08.463Z
2020-08-18T00:13:08.463Z
user1271772
<p>(Please excuse my English)</p>
<p><a href="https://i.sstatic.net/OLbsP.gif" rel="noreferrer"><img src="https://i.sstatic.net/OLbsP.gif" alt="Earth without water" /></a></p>
<p>The picture above is an image of the Earth without water. We know that the picture above is a very exaggerated one. If the Earth were to shrink to the size of the picture above, it would look like a very smooth and round sphere.</p>
<p>I wonder what it would look like if the Earth were reduced to the size of a basketball. I think the basketball-sized Earth will have a smoother surface than actual basketball. But I don't know how smooth the surface of the basketball-sized Earth will be.</p>
<p>What would the basketball-sized Earth look like? Will it look like a marble ball with shinning smooth surface?</p>

CC BY-SA 4.0
2020-08-17T07:08:04.020Z
I am sure I used less spherical than the Earth basketballs to play basketball some 30 years ago. Some of them were brand new. I am not sure the balls are much better today.
fraxinus
CC BY-SA 4.0
2020-08-17T09:27:46.063Z
[Earth's density is about 5](https://chem.libretexts.org/Bookshelves/Ancillary_Materials/Exemplars_and_Case_Studies/Exemplars/Physics_and_Astronomy/Density_of_Black_Holes). You've just increased that by a factor of about 1E23. Since black holes come in around 4E14 I think the surface will look like a very dark hole.
candied_orange
CC BY-SA 4.0
2020-08-17T09:35:55.523Z
The portrayed image, and related ones, can be found at many sites on the internet. The typical description of what that image portrays is [not even wrong](https://en.wikipedia.org/wiki/Not_even_wrong).
David Hammen
CC BY-SA 4.0
2020-08-17T10:08:04.477Z
@candied_orange you need to compress the Earth some more (into about 1cm size) in order to get a black hole. Black holes can have any density and their density depends on their mass (large black holes are less dense than small ones)
fraxinus
CC BY-SA 4.0
2020-08-17T12:52:27.160Z
@a_donda - It shows the geoid height variations, the difference between the geoid (a surface of constant gravitational+ centrifugal  potential) and the best fit oblate spheroid that contain the same volume. The deviations between the two are small, ± 150 meters IIRC.
David Hammen
CC BY-SA 4.0
2020-08-17T15:51:12.990Z
Relevant [xkcd What If?](https://what-if.xkcd.com/46/)
agweber
CC BY-SA 4.0
2020-08-17T17:06:17.163Z
Bowling balls and billiard balls are supposed to be very smooth (ignoring the three holes on a bowling ball). Basketballs are intentionally unsmooth. There are patents galore on how to manufacture a large (29.5 inch circumference) ball so that it is "generally round", bounces well and predictably, but can be held with one sufficiently large hand.
David Hammen
CC BY-SA 4.0
2020-08-18T07:19:00.047Z
A way to "guesstimate" the impact of removing all water can be, imo, attained by looking at : https://www.usgs.gov/special-topic/water-science-school/science/how-much-water-there-earth and especially https://www.usgs.gov/media/images/all-earths-water-a-single-sphere : it shows how little all of earth's water really is (and how tiny liquid fresh water is)
Olivier Dulac
CC BY-SA 4.0
2020-08-18T20:56:41.960Z
Related: https://skeptics.stackexchange.com/questions/10763/is-earth-as-smooth-as-a-billiard-ball
Jason Goemaat
CC BY-SA 4.0
2020-08-19T03:03:23.747Z
[No, That’s NOT What the Earth Would Look Like Without Water](https://slate.com/technology/2015/09/earth-without-water-nope.html)
David Hammen
<earth-observation>
Comparing the Earth with a basketball?
pdh0710
# Comparing the Earth with a basketball?

(Asked by: username_0 on 2020-08-16)

(Please excuse my English)

[![Earth without water](https://i.sstatic.net/OLbsP.gif)](https://i.sstatic.net/OLbsP.gif)

The picture above is an image of the Earth without water. We know that the picture above is a very exaggerated one. If the Earth were to shrink to the size of the picture above, it would look like a very smooth and round sphere.

I wonder what it would look like if the Earth were reduced to the size of a basketball. I think the basketball-sized Earth will have a smoother surface than actual basketball. But I don't know how smooth the surface of the basketball-sized Earth will be.

What would the basketball-sized Earth look like? Will it look like a marble ball with shinning smooth surface?

**Tags:** earth-observation

> **Comments:**
> **username_1**: I am sure I used less spherical than the Earth basketballs to play basketball some 30 years ago. Some of them were brand new. I am not sure the balls are much better today.  
> **username_2**: [Earth's density is about 5](https://chem.libretexts.org/Bookshelves/Ancillary_Materials/Exemplars_and_Case_Studies/Exemplars/Physics_and_Astronomy/Density_of_Black_Holes). You've just increased that by a factor of about 1E23. Since black holes come in around 4E14 I think the surface will look like a very dark hole.  
> **username_3**: The portrayed image, and related ones, can be found at many sites on the internet. The typical description of what that image portrays is [not even wrong](https://en.wikipedia.org/wiki/Not_even_wrong).  
> **username_1**: @username_2 you need to compress the Earth some more (into about 1cm size) in order to get a black hole. Black holes can have any density and their density depends on their mass (large black holes are less dense than small ones)  
> **username_3**: @a_donda - It shows the geoid height variations, the difference between the geoid (a surface of constant gravitational+ centrifugal  potential) and the best fit oblate spheroid that contain the same volume. The deviations between the two are small, ± 150 meters IIRC.  
> **username_4**: Relevant [xkcd What If?](https://what-if.xkcd.com/46/)  
> **username_3**: Bowling balls and billiard balls are supposed to be very smooth (ignoring the three holes on a bowling ball). Basketballs are intentionally unsmooth. There are patents galore on how to manufacture a large (29.5 inch circumference) ball so that it is "generally round", bounces well and predictably, but can be held with one sufficiently large hand.  
> **username_5**: A way to "guesstimate" the impact of removing all water can be, imo, attained by looking at : https://www.usgs.gov/special-topic/water-science-school/science/how-much-water-there-earth and especially https://www.usgs.gov/media/images/all-earths-water-a-single-sphere : it shows how little all of earth's water really is (and how tiny liquid fresh water is)  
> **username_6**: Related: https://skeptics.stackexchange.com/questions/10763/is-earth-as-smooth-as-a-billiard-ball  
> **username_3**: [No, That’s NOT What the Earth Would Look Like Without Water](https://slate.com/technology/2015/09/earth-without-water-nope.html)  

---

## 3 answers

### Answer by username_3 on 2020-08-17. Score: 38

> The picture above is an image of the Earth without water. We know that the picture above is a very exaggerated one.

**About the image**

The image shown in the question is very widely claimed to show an image of the Earth without water. A google image search for that image comes up with the nice logo "earth form without water". This image pops up on the internet again and again. This image does not show an Earth without water, even greatly exaggerated.

Note that the image in the question has a fuzzed out title and legend. All of the images on the internet that claim this is an image of the Earth without water have a fuzzed out title and legend. A non-spinning version of that image with the correct title and legend is below. (I do not like reading around animated gifs.)

[![Exaggerated image of the Earth's geoid height, with legend](https://i.sstatic.net/m5eh9.png)](https://i.sstatic.net/m5eh9.png)
Source: Bezděk, Aleš, and Josef Sebera. "Matlab script for 3D visualizing geodata on a rotating globe." Computers & Geosciences 56 (2013): 127-130.

The above image is by the author of the image. The title says what the image shows, which is the geoid height. The legend shows that the variation from the highest to lowest geoid height is less than 200 meters. Compare that with the 19.777 km altitude difference between the highest mountain above sea level and the deepest trench below sea level. The image shows the Tibetan plateau as below the reference ellipsoid and shows the Java trench (not visible in the above) as above the reference ellipsoid. This is not a world without oceans.

**So what does the image show?**

What the image does show is the geoid height, greatly exaggerated. A geoid is the surface of constant gravitational plus centrifugal potential that is the best fit in a least squares sense to mean sea level. In other words, the geoid portrays the Earth's gravitational field. A simpler model of mean sea level is an oblate ellipsoid. The geoid height at some point is the altitude difference between corresponding points on the geoid and on the reference ellipsoid. Red areas in the image (positive geoid height) show where the geoid is above the reference ellipsoid while blue areas (negative geoid height) show where the geoid is below the reference ellipsoid.

Look at the Tibet Plateau in the rotating image. It is blue, which means the geoid there is below the reference ellipsoid. Look at the Java Trench. It is the very deepest red, which means the geoid there is above the reference ellipsoid. The Rocky Mountains are white, no different than the rest of the northern North America. The Alps are reddish, but not as red as is the eastern North Atlantic.

The Tibet Plateau shows up as a depression in this image instead of as a large elevated land mass because it is are very large blob of rock that has less than average density. The rock near the Java Trench is very dense basalt.

The image does not represent anything close to what many say it represents. The image does represent what the author intended it to represent. The image is interesting to those who know what the image portrays. The problem is that the image is so often described incorrectly.

**An image of the Earth without water**

An image of the Earth without water, slightly exaggerated, is shown below.

[![An image of the Earth with all of it waters gathered into a ball about 1365 km across hovering over the western US](https://i.sstatic.net/Mo0hC.jpg)](https://i.sstatic.net/Mo0hC.jpg)
Source: : Jack Cook, Woods Hole Oceanographic Institution, Howard Perlman, USGS, [Astronomy Picture of the Day 2012 May 15](https://apod.nasa.gov/apod/ap120515.html)

The Earth is round rather than lumpy. For portrayal purposes, a ball of water about 1365 km across hovers over the western US. That ball represents all of the Earth's surface waters.

  

**Comparison to a basketball**

The difference between the Earth's equatorial and polar radii is about 21.385 km. The difference between the height of the highest mountain on the Earth above sea level and the Earth's deepest trench below sea level is about 19.777 km.

Shrinking these down to the size of a basketball with a circumference of 29.5 inches (I used US units because that is what NBA regulations specify) shrinks the 21.385 km difference between the equatorial and polar radii to a mere 0.4 millimeters, shrinks the height of Mount Everest above sea level to 0.165 millimeters, and shrinks the depth Challenger Deep below sea level to 0.204 millimeters.

A basketball is supposed to be round(ish). That the Earth's polar radius is 99.66% of its equatorial radius makes the Earth fairly "roundish". The roundness of the Earth is in line with the roundness of a billiard ball, and probably for a basketball. (While I did find roundness requirements for a billiard ball, I was unsuccessful in finding roundness requirements for a basketball.)

What about smoothness? Basketballs are not smooth. They are intentionally designed with stipples (pebbles) and channels so as to make basketballs easier to handle. There are patents galore regarding the size, shape, and placement of those pebbles and channels. The pebbles are a bit higher than 0.17 millimeters and the channels are significantly deeper than 0.2 millimeters. The Earth is smoother than a basketball because basketballs are unsmooth by design.

> **Comments:**
> **username_3**: @Emil - I added a comparison with a basketball. The image in the question is one that I do not like because of the way it misrepresents the Earth and the way it is misrepresented on the internet. Look at the Himalaya in that image. They are blue. Rather deep blue. The geoid is below mean sea level at the Himalaya. The deepest red (the highest) is in the ocean, offshore of Indonesia. There is a deep trench there, not as deep as the Marianas Trench, but still, it's deep.  
> **username_3**: @username_0 - It is not your fault. It is the fault of the people who created that image, and even more so, it is fault of the many people who have incorrectly promulgated that image across the internet. No matter what exaggerations one applies, this is not how the Earth looks, with or without water.  
> **username_7**: So interestingly, the Himalaya would have about the height of one of the basketball pebbles!  
> **username_8**: @username_7 Much smaller.  
> **username_9**: Now your answer makes me want to know how Earth compares to the required roundness for billiard balls :)  
> **username_3**: @username_9 - IIIRC, Phil Plait ("the Bad Astronomer") compared the Earth to a billiard ball and wrote that the roundness of the Earth is well within spec, but that the smoothness was not. Those who have played pool in a bar or a pool hall know that when racking the balls, one has to rotate the balls on the corners of the rack just right so that they roll towards the other balls in order to result in a nice tight rack. If one doesn't do tha, there will be a few balls that move a lot the break and a cluster of balls that don't move much at all. The table isn't flat and the balls aren't quite round.  
> **username_7**: @username_8 Himalaya is  8km/12700km = 6.3E-4 , and the basketball pebble is 0.17mm/238.8mm = 6.7E-4.  

---

### Answer by username_10 on 2020-08-17. Score: 6

The deviations of Earth from a sphere are of order 20 km. This approximates both the difference between equatorial and polar radii (defining an ellipsoid) and the difference between the highest and lowest points (Mount Everest and Mariana Trench) relative to the ellipsoid. A basketball is about 50 million times smaller than Earth, and the corresponding deviations on a basketball would be 0.4 mm.

The [depth](https://www.productplayoffs.com/best-indoor-basketball/) of the main grooves or "ribs" on a real basketball is about 2 mm. I am unable to find a source for the thickness of the numerous bumps or "pebbles" on a real basketball, but it is plausibly close to 0.4 mm. Thus, the bumps that cover the ball are somewhat to scale with the largest 20 km features of Earth, though of course Earth does not have such density of 20 km features.

> **Comments:**
> **username_3**: I have found patents galore regarding basketballs. Patents on basketballs go back almost 100 years. The first one I found dates back to 1928. Yet very few recent basketball patents cite **any** prior art (what???).  Not a single one of those patents I read specified how deep the channels are or how large the pebbles are. I'm used to reading patents that give exquisite detail that would let me recreate the object in question if I had the requisite skills and equipment. That's not possible with the basketball patents I have read.  
> **username_3**: BTW, welcome aboard the Astronomy Stack Exchange. Nice answer.  
> **username_3**: And with the migration, welcome aboard the Earth Science StackExcange!  

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### Answer by username_11 on 2020-08-18. Score: 1

A basketball is a ***sphere*** while Earth is an ***oblate spheroid***, meaning Earth's equatorial radius is larger than its polar radius (as mentioned already in [username_3 username_3's answer](https://earthscience.stackexchange.com/a/20078/18946) and [username_10's answer](https://earthscience.stackexchange.com/a/20079/18946), I have just introduced the *name* for this phenomenon).

**What exactly is an [oblate spheroid](https://en.wikipedia.org/wiki/Spheroid)?**

If you take an ellipse and rotate it around its major (longer) axis you get a prolate spheroid, much like an Australian football:

![](https://i.sstatic.net/E0rG2.png)

If you rotate the ellipse around its minor (shorter) axis, you get an oblate spheroid, more like a lentil, M&M chocolate, or mandarin fruit:

![](https://i.sstatic.net/j4qQI.png)![](https://i.sstatic.net/dFd4z.png)

Here are the oblate and prolate spheroids side-by-side:

![](https://i.sstatic.net/3kjAS.png)

This is a sphere:

![](https://i.sstatic.net/v6YIr.png)![](https://i.sstatic.net/uIyrU.png).

**Earth is an oblate spheroid, so a basketball is not the best model. A mandarin fruit is better.**

> **Comments:**
> **username_12**: Yes, the Earth is an oblate spheroid, but barely. It's much closer to a perfect sphere than to a mandarin, which is visibly oblate.  
> **username_11**: The mandarin in my picture is not so oblate.  
> **username_12**: I can see without measuring it that the mandarin is oblate. I can't see without measuring that the Earth is oblate. To the naked eye, the Earth looks perfectly spherical.  
> **username_3**: The mandarin in your picture is visibly oblate. The Earth is not visibly oblate. A visibly oblate basketball would not pass referee inspection. The Earth shrunken to the size of a basketball most likely would pass inspection on the basis of roundness.  
> **username_6**: I would think the basketball on the ground would be an oblate spheroid as well.  The Earth's oblateness is about 1/1000th it's diameter.  Basketballs are inflated to 8 psi and are made of somewhat stiff material, but the weight would tend to squish it just a little.  With a radius of 4.5 inches looking down the circular area would be about 64 square inches.  Very roughly 512 pounds of pressure tending to overcome gravity and keep it spherical.  However the weight of 22 ounces would tend to flatten it, making it oblate.  The ratio is 1/372, about 3 times the Earth's oblateness.  
> **username_13**: @username_6 And here I thought to recall that the Earth's oblateness was 1/298, so surprisingly close to your back-of-the-envelope oblateness of a basketball  
> **username_6**: @username_13 you're right, don't know what I was thinking....  Used the km difference in radius from another question and a misremembered diameter of the Earth  

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