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# Shape of the Earth: The Oblate Spheroid

“Earth is not a perfect sphere. Its shape is an oblate spheroid. This just means that it flattens at the poles and widens out at the equator.”

Earth bulges at the equator because of the centrifugal force during rotation. Like spinning a pizza, the mass pushes outwards and flattens out along the axis of rotation.

This phenomenon occurs because the rotational speed at the equator is greater than at higher latitudes.

In this article, you’re going to learn about the shape of the Earth and why it’s an oblate spheroid.

### Earth radius as a datum

Geographers model Earth’s shape as an ellipsoid, which is a sphere slightly flattened at the poles. They use a datum to reference geographic coordinates on Earth.

A datum describes the shape of the Earth in mathematical terms. It defines the radius, inverse flattening, semi-major axis, and semi-minor axis for an ellipsoid.

For example, the WGS84 datum identifies the longest diameter of an ellipse (semi-major axis) as 6,378,137.0 m. Next, the semi-minor axis is 6,356,752.3 m.

So, this aligns well with the radius of Earth at the equator as 6,378 km. Finally, the squashing at the poles is slightly less at about 6,357 km.

### Why Mount Chimborazo is higher than Mount Everest

If you stand at mean sea level at the equator, you would be 21.4 km farther away from the center of Earth compared to standing at the North and South Pole.

This is because the equator bulges and forms an oblate spheroid. So if you measure from the center point of Earth outwards, Mount Chimborazo is the highest point on Earth because of the equator bulge height advantage.

But if you compare height above mean sea level, then Mount Everest is the tallest mountain. While Mount Chimborazo has a peak elevation of 6,263 m, Mount Everest towers at 8,848 m tall.

### Shape of the Earth: The Oblate Spheroid

Earth’s equatorial bulge, a distinctive feature of our planet, arises as a consequence of its rotation.

Much like spinning pizza dough, the centrifugal force generated by the Earth’s rotation pushes mass away from the axis of rotation, leading to a flattening effect at the equator.

The shape of the Earth is an oblate spheroid, meaning that its two bulges are slightly different sizes when you compare the equator to the poles.

Got any questions or comments? Make sure to get back to us by using the comment form below.

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1. earthhow says:

Not 100% sure, the more I think of it… Although the shape of the earth is not a perfect sphere, the rotation and climate has been stable for centuries. I might be wrong though but I’d say effects are small. Please reply if you find something different.

2. Donna says:

Because of the shape of the earth – it seems the rotation would also be off just a little and thus the temperature of the earth would always be changing ever so little. Like is fact from Greenland history, while glaciers recede in some areas they advance in others. Temperatures changing around the world offers us new farmland into perpetuity!

3. Kenliey Jordan says:

I believe the Earth is flat and the atmosphere makes it look round. Everyone says it’s round because of the look of the pictures people take of it but I still believe it’s flat!

Unique information

5. PJ says:

Guys I think you need to look at these 2 things.

————–THING 1—————
someone asked this question on “USA Today” website (I’ll try post link).

Question: Why do flights from the USA to Asia travel far north (above Alaska/Siberia) rather than the seemingly more direct “straight line” across the Pacific?
—submitted by reader John, Parrish, Fla.

Answer: It is shorter to fly the Great Circle route than a straight line due to the circumference of the earth being so much greater at the equator than near the poles.
——————–END THING 1————————–

You here are saying the difference is not noticable to the human eye.
Yet these planes are taking routes that are twice as long. That doesn’t make sense.

—————THING 2——————–
Look at how every plane from central Europe flies over Ireland, all the way over Alaska, to mid and even south USA.

Yet, every real photo you supposedly see of the earth from space does not show anything anywhere near noticeable. Yet they take these routes almost twice as far.

SOMEONE IS LYING!

Now find a flat earth map……the disc shape…..
Draw a line on flat earth map from say, Frankfurt to Washington. Notice how it actually does cross Ireland and Alaska to reach Washington, in a straight line.

To make those very curved (globe map) routes shorter (as claimed by the captain / USA today BS) the earth would indeed have to be very squashed such as a rugby/american football!)

So who is lying? NASA? The Government? USA today?

The flat earth maps are much older than flight paths……and apparently much more accurate!

Just for more evidence that someone is lying and has been for a very long time.

Also look at how the few planes travelling across the mid Atlantic e.g., from Miami to Madrid. How come they go in a straight line? Now look at flat earth again. Draw a line between Miami and Madrid.

6. Ground Control to Major Tom says:

I don’t see a picture of Earth as an oblate spheroid, all I see are lines on an oblate spheroid and then I am told that this is the shape of Earth? not one image even if it’s too small for the naked eye to see then why would we say it is an oblate spheroid if we couldn’t see it? According to Neil D. Tyson, “we are a little chubby on the bottom, an oblate spheroid but more pear-shaped”
Chubby on the bottom, Antarctica, not the equator, as you show in you drawings above.

7. Mayram says:

It’s very simple notes that any student can understand.

8. Cosi says:

Benjamin,
None of the photos show a perfect sphere. You are plain wrong to make such an assertion, simply because of your intuition.
As explained by others, above, the difference is so tiny it is not discernible to the naked eye, especially when other shapes, cloud formations and lighting conditions are involved.

9. Paul Derrington says:

William Sterling, centrifugal force has a very low effect on gravitational force. Imagine being on one of those old playground merry-go-rounds. If that thing was spinning 1000 miles per hour it would sling everything on it off without problem. Going just a few miles per hour it would do it as well by the way! So the reason we are not slung off the Earth is due to gravity. Gravity has to do with the Mass of the Earth and not the spin of the Earth. The Mass of the Earth is so large it holds you and everything else down. To the Earth your body mass is not even like a speck of dust.

10. Bruce Hamilton says:

In order to have a “perfect sphere” the picture would need a low enough resolution to shave off mountains and fill valleys. So every. Single. Damn. Photo. Is an approximation at best.

11. Jim Bob says:

Ben, are you the one making the claim the picture you are looking at show a 100% perfect sphere, or is someone els making that claim? If your making the claim then your only arguing with your self, which is where the logic should start. How about you walk the earth your self to prove your self right, this way you can reassure your self that your the genius we’ve all been waiting for. In order to be great you have to prove your findings otherwise your just a talker . Get a laser.. you can figure the rest out. And if it’s flat, what do we do next?

12. Antonia Bellini says:

I would like to add that the reason it takes me almost as long to fly from Italy to Toronto as it does to fly to Vancouver, clear across the continent, is because the earth is an oblate spheroid shape, and when they fly directly to Vancouver they take the ARCTIC route, and since the earth is flatter up there it’s less distance than it would be if it bulged out the same amount as it does further south. If I have to fly to Toronto first, this adds 6 -7 hours of flying.

13. William Sterling says:

This question highlights the issue of the claim of the oblate shape of the Earth; Why do objects on the Earth’s surface weigh the same at the Poles (where there is NO centrifugal force) as they do at the Equator (where centrifugal force of rotation is at its maximum)? If there IS no difference, how can any scientific experiment or conclusion on the surface of the Earth concerning weight be reconciled? How can Earth’s rotation be proven using gravity as a factor without centrifugal force?

14. Benjamin Beckett says:

There’s only a 0.3% difference. as BD said, do you REALLY think you’ll notice that?

15. BD says:

There’s only a 0.3% difference.. Of course you won’t see that difference in a picture.

If the earth had a radius of 10cm at the poles it would have a radius of 10,03cm at the equator. That’s a 0.3mm increase, you would not notice that difference unless you measured it with precision tools.

Let’s look at another analogy. If you have one dude that’s 175cm tall and another that’s 0.3% taller he would only be 175.5cm tall. Would you be able to tell which one of them were taller in a picture? No, you would not.

16. Benjamin Joachimi says:

But Every. Single. Damn. Photo. taken from space by astronauts shows a perfectly spherical Earth. Every single one. Those photos are not faked as flat earthers like to say – they are real. The oblate Earth theory is therefore known to be false.