Rather they maintain irregular, fragmentary shapes. Answer originally posted July 30, Sign up for our email newsletter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. Earth is 0. Since they're not even one whole percentage point thicker in the middle, it's safe to say they're very round. As for Uranus and Neptune, they're in between. Uranus is 2. Neptune is 1. They're not perfectly round, but they're pretty close.
Do you want to know what it's like to be a spinning planet? You can feel it when you spin around in place. First, make sure there are no obstacles around that you might bump into. Then either while standing, or in a spinner chair, spin around in circles.
Hold your arms close to your body, then extend your arms out. Move your arms in and out and feel the difference. When your arms are outstretched, your hands have to move faster than your shoulders to keep up, so you'll feel more force on them.
Why Are Planets Round? The Short Answer:. A planet is round because of gravity. Feel the forces from spinning Do you want to know what it's like to be a spinning planet? If you liked this, you may like: What Is a Barycenter? None of the planets in our solar system are perfect spheres, nor for that matter is our sun. All those bodies could more accurately be described as "oblate spheroids. To borrow an analogy from the astronomer Phil Plait, they look like a basketball that someone is sitting on.
Put more technically, in a celestial body with an oblate spheroid shape, the polar circumference will be smaller than the equatorial one. So here on Earth, if you were to travel from the North Pole to the South Pole and back, you'd have walked a grand total of 24, miles 39, kilometers. On the other hand, a complete trip around the equator would be a bit longer.
That's because the circumference of Earth's equator is 24, miles 40, kilometers. As such, when you stand at sea level on the equator, you're farther away from the center of our planet than you would be at either pole. On some other planets, this bulge is even more pronounced. Just look at Jupiter. Earth is only 0. But Jupiter's measurements showcase a much bigger disparity.
Indeed, astronomers have found that this plus-sized planet is a full 7 percent wider at its equator than it is between the poles. The oblate spheroid shape is the result of two main factors: gravity and rotation. Troy Carpenter, director of Washington State's Goldendale Observatory, recently discussed the matter with us in an email exchange.
That's because all objects experience self-gravity, a force which pulls their atoms toward a common center. As the mass of an object increases, so too does its self-gravitational pull. After it exceeds a certain mass, the pull gets overpowering to the point where the object collapses onto itself and becomes spherical.
Little items — like, say, a banana or a lug wrench — can resist this fate because their self-gravity is relatively weak, allowing them to retain non-spheroid shapes. However, in planets, suns and other truly massive bodies, the force is so strong that they can't avoid being distorted into spheroids. While gravity conspires to render the planets spherical, the speed of their rotations is simultaneously trying to flatten them.
The faster a celestial body spins, the more disproportionate its equatorial bulge gets. A significant percentage of stars in the sky rotate much faster and bulge noticeably at their equators.
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