Is the Earth Round?

The Earth isn’t flat, that’s for sure. And if you look at a photograph, the Earth really looks round. But how round is it?

The actual shape of the Earth is actually an oblate spheroid – a sphere with a bulge around the equator. The Earth is bulged at its equator because it’s rapidly rotating on its axis. The centripetal force of the rotation causes the regions at the equator to bulge outward. And it actually makes a pretty big difference. The diameter of the Earth, measured across the equator is 43 km more than when you measure the diameter of the Earth from pole to pole.

This bulge has some interesting implications. For example, it means that the point on Earth furthest from the center isn’t actually Mount Everest, but Mount Chimborazo in Ecuador. Only because Chimborazo is closer to the Earth’s equator.

So how smooth is the Earth. When billiard balls are manufactured, they aim for a tolerance of 0.22%. The Earth has a tolerance of 0.17%, so it’s actually smoother than a billiard ball. If you could hold the Earth in your hands, it would feel smoother than a billiard ball.

But the Earth definitely isn’t flat.

We have written many articles about the Earth for Universe Today. Here’s a cool article about looking at the Earth as if it’s an extrasolar planet.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.