Technically, Earth Does Not Orbit Around the Sun

Technically, Earth Does Not Orbit Around the Sun
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The discovery that Earth revolves around the Sun was revolutionary. It fundamentally changed how we viewed the cosmos, as well as ourselves.

But the Earth does not revolve around the Sun. At least, not exactly. Time to get pedantic.

"Technically, what is going on is that the Earth, Sun and all the planets are orbiting around the center of mass of the solar system," writes Cathy Jordan, a Cornell University Ask an Astronomer contributor.

"The center of mass of our solar system very close to the Sun itself, but not exactly at the Sun's center."

Every single object in the solar system, from the gargantuan sun to the tiniest speck, exerts a gravitational pull on everything else. The solar system is basically a massive game of tug of war, and all of the yanking balances out at a specific point: the center of mass, or "barycenter." Everything in the solar system orbits around that point. Sometimes, it's almost smack dab at the Sun's center. Right now, the barycenter is just outside the Sun's surface. But it's constantly changing depending upon where the planets are in their orbital paths.

 

Because the Sun holds 99.87% of all the mass in the solar system, it's always going to win the tug of war. Even if all the planets were perfectly lined up on one side of the Sun, the center of mass would be just 800,000 kilometers off the surface of the Sun. That sounds like a lot, but remember, our solar system is big! Such a barycenter would be roughly 70 times closer to the Sun than the closest planet to the Sun, Mercury.

 

 

An even better illustration for center of mass is the binary star system. When two stars of comparable mass cohabit the same corner of space, they orbit about a point between each other.

 

 

However, rather than play a billion-year game of cosmic tag, more often than not, binary stars will take an elliptical orbit!

 

File:Orbit5.gif

 

The rest of the universe certainly doesn't revolve around the Earth, but, like so many topics in science, it's an oversimplification to say that everything orbits around the Sun.

(Images: Chandra Observatory, Wikimedia Commons, Lsmpascal, ESO, Zhatt

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