# Is the Earth really round?

1. Nov 20, 2017

### Jacinta

I mean it would be impossible for Earth to be fully spherical as it would be too bumpy to be a sphere shape.

If this is the case, why is Earth considered round?

2. Nov 20, 2017

### phinds

'Cause it's close enough for government work. You do the math. Figure out the tallest mountain as a percentage of the radius of the Earth.

Also, you forgot to mention tidal bulge and deformations due to (1) mass distribution differences and (2) the fact that the Earth is spinning.

Oh, and by the way, it is NOT considered round by scientists when they are being precise. That's just a pop-science simplification.

3. Nov 20, 2017

### OmCheeto

Because it looks round?

hmmm.... I think this would make an interesting experiment:

Find the highest resolution image of the earth from outer space, and see if you can detect a difference in diameter when measuring along the equator vs from pole to pole.​

The highest resolution image I've found so far is 11,500 x 11,500 pixels, at NASA. [ref] Though, they claim it's a composite, and they claim there are even larger composites!

4. Nov 20, 2017

### I like Serena

Hi Jacinta!

On a scale where we can see the entire earth, it's pretty hard to see that the earth is not exactly a sphere.
We should not be able to distinguish any mountain, since even the highest mountain is insignificant in comparison with earth's size (0.15%).
If we see anything, it's that the earth is about 0.5% bigger on the equator than on the poles as @OmCheeto mentioned.
The earth is probably closer to a sphere than anything in every day life that we consider spherical.

5. Nov 20, 2017

### Jacinta

I don't think this looks very spherical??? Looks more like my cats chew toy.

This is a sphere.

6. Nov 20, 2017

### CWatters

Because the earth spins the radius is about 13 miles greater at the equator than the poles.

7. Nov 20, 2017

### Jacinta

But it's dumb, shouldn't scientists do something about this? A sphere is something you can roll around, I don't think you can roll around the Earth.

8. Nov 20, 2017

### Jacinta

So, in simple terms, you think that the Earth decreases in miles closer to the equator?

9. Nov 20, 2017

### CWatters

Increases.

10. Nov 20, 2017

### Jacinta

How? Isn't the equator fatter than the north pole?

11. Nov 20, 2017

### I like Serena

Indeed. That doesn't look spherical at all.
It looks more like a model of the earth that a cat chewed on!

For reference, earth actually looks like this:

12. Nov 20, 2017

### Janus

Staff Emeritus
Would you consider a billiard ball as being spherical? If so, if you were to scale the Earth down to the size of billiard ball, the roughness of it surface due to mountains a valleys would be less than the manufacturing tolerances for irregularities for a billiard ball. Even including the equatorial bulge leaves the Earth pretty close to that tolerance.

13. Nov 20, 2017

### Jacinta

From a far it gives off a spherical illusion, but it actually looks like a cats chew toy.

14. Nov 20, 2017

### Jacinta

Yes, because a billiard ball can roll around.

The Earth can't roll around but spin around, there is a difference.

15. Nov 20, 2017

### Jacinta

Rolling:

Spinning:

16. Nov 20, 2017

### I like Serena

But... a Simpson that can spin can also roll can't he?
Round or not.

17. Nov 20, 2017

### Jacinta

That's because his body sideways is rollable because of his cylinder shape.

We are discussing spheres.

18. Nov 20, 2017

### Ken Fabos

Jacinta @5 - this -

- is not an image of the Earth as it is, but is an artificially created image intended to show something other than the Earth's physical shape. Not sure exactly what it shows - gravitational potential of Earth with oceans removed maybe?

This is an image of the Earth - ( in this case, showing the shadow of the Moon during an eclipse in 2017)

19. Nov 20, 2017

### phinds

No, it's just standard pop-science. YOU do something about it if you actually imagine that you are going to change the culture of popular science reporting. Saying that popular science reporting is dumb is a tautology and a waste of breath.

20. Nov 20, 2017

### Jacinta

Interesting.

21. Nov 20, 2017

### Staff: Mentor

The Earth could roll if it had something to roll on. It's wobble would not be noticeable; it is way too small. It would roll better than a baseball or soccer ball.

22. Nov 21, 2017

### gmax137

23. Nov 21, 2017

### Spinnor

Expand the shape of the Earth in terms of spherical harmonics. The leading term is a perfect sphere, all other terms are so small that to a first approximation, and a very good one at that, the Earth is a perfect sphere.

24. Nov 21, 2017

### CWatters

I thought it might be an idea to find out where that first image in #5 came from and what it represents. That has proved difficult.

It seems to appear in press coverage of the launch of the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite in 2009, so clearly it's older than that.

Then I found it in a German article written and edited between March and November 2002 about the GRACE satellite which launched in March 2002. However all the images on the GRACE web site appear to be higher resolution (I mean the show changes in gravity in more detail not the image resolution).

My guess is it's either an early image from GRACE or it might be from CHAMP which was launched in 2000 I think.

Anyway its most likely an image of the earth modified to show how gravity varies due to changes in density and the like.

25. Nov 21, 2017