Radius of the Earth
Written by Fraser Cain
The average radius of the Earth, or the distance from the center to surface is 6,371 km, or 3,959 miles.
But wait, the answer is actually a little more complicated than that. As you probably know, the Earth is rotating on its axis, completing one full revolution in just less than 24 hours. This relatively rapid rotation causes the Earth's poles to flatten, and our planet bulges at the equator. Instead of a perfect sphere, the Earth is a flatted sphere.
This means that the distance from the center to the equator is further than the distance from the center to the Earth's poles. The equatorial radius of the Earth is 6,378.1 km, and the the polar radius of the Earth is 6,356.8 km. Subtract those two numbers and you get 21.3 km. In other words, points on the equator are actually 21.3 km further from the center of the Earth than the poles.
This is why I said at the top of this article that the average radius of the Earth is 6,371 km.
One of the interesting implications of this is that the point most distant from the center of the Earth is actually Mount Chimborazo in Ecuador. It's 6,267 meters tall, but it's very close to the equator, while Mount Everest (although taller), is more distant. Mt. Chimborazo is 6,384.4 km from the Earth's center, while Mt. Everest is only 6,381.7 km from the center. Mt. Chimborazo is a little less than 3 km further from the center of the Earth than Mt. Everest.
We have written many articles about the Earth for Universe Today. Here's an article about the circumference of the Earth, and here's one about the diameter of the Earth.
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.
Filed under: Astronomy
