Styrofoam balls were a staple for planetary science projects in elementary school. What our teachers didn’t get into, though, was that Earth as we know it isn’t a sphere, and in a game of marbles it wouldn’t fare too well. That’s because it experiences something called polar flattening, making it a squashed sphere, like if someone stepped on your styrofoam ball you painstakingly puffy-painted.
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Earth alone does come close to being perfect, but its rotations flatten it at the poles, making the equator bulge. The technical term for this irregularity is “oblate spheroid,” which means the distance from the center of the Earth to sea level is greater than the distance of the center to a pole. If this is hard to imagine, picture a basketball as Earth’s average shape. The spinning compresses the ball down as though someone stepped on it about 1/32 of an inch. That may not seem like a lot, but if you scale it to a cosmic level, that makes the equator bulge roughly 13 miles (about 22 kilometers) more than the polar radius. Incredibly, this means that while the mountain with the highest altitude on Earth is Nepal’s Mount Everest, the furthest from the geocenter is Mount Chimborazo in Ecuador, which gets a boost from being close to the equator.
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Earth has more lumps, too — and that means it’s not even a perfect oblate spheroid! If our planet had to shop, it would likely opt for clothing for what women’s magazine guides would call a pear-shaped body. The varying distributions of mass makes the southern hemisphere a little more, well, girthy. Plus, water and mountains and tectonic movements vary the Earth’s gravitational field as they change the pull of gravity. Constantly shifting plate tectonics also keep the Earth cozy, Universe Today explains, because the planet’s geological plasticity allows new crust to form — and that’s critical for Earth’s meticulous recycling of carbon to keep it from becoming a hellish landscape.
In case recent flat-Earth hubbubs distracted you from the truth, the notion that Earth was even spherical first popped up in ancient Greece during the 6th century BCE. The first person to suggest our planet isn’t a foolproof sphere (on record, anyway) was Isaac Newton, the eponymous hero of the laws of motion. Other stars and planets have love handles, too, like Saturn and Jupiter and a quick-spinning star named Altair. But if your teacher grew up with Carl Sagan and considered Earth a big blue marble, then it’s okay to gloss over the truth a little with a dab of glitter.