Earth orbiting the sun Infographics

The Earth Doesn’t Actually Orbit The Sun?


You were taught that Earth and other planets in our solar system orbit the sun, and that our solar system orbits the center of the Milky Way. Did your science teacher have it wrong? Is everything you’ve learned about physics and gravity wrong?

The Earth Doesn’t Actually Orbit The Sun?

For all practical purposes, what you were taught wasn’t entirely wrong. The Earth does in fact orbit the sun. In the strictest sense, however, it doesn’t.

The sun and other planets each have their own gravity well which interact and pull on one another. The result of this, is that everything in an orbital system (like our solar system) orbit the center of mass of the system. This ‘center of mass’ is called the barycenter. The Earth, the sun and everything else in our solar system orbit this barycenter – not the sun.

The Barycenter Of Our Solar System

The Barycenter Of Our Solar System

Where Is The Barycenter?

In a single star system like ours, most of the time (but not always), the barycenter is located somewhere within the star itself. However, most barycenters continuously change as massive objects (like planets) orbit a star.

If an unusual alignment happens where a large percentage of mass is on one side of the star, the barycenter can exist outside of the star’s radius. In cases of 2 star systems, the barycenter will be located between the two stars. If the stars aren’t of the same mass, it will be closer to the heavier, or more massive one.

Bonus Fact: The Earth doesn’t even orbit where the barycenter currently is. It orbits where it was roughly eight minutes ago. If the sun suddenly vanished, we would continue to our orbit it for another 8 minutes before shooting off on some random tangent because gravity isn’t instantaneous – it propagates at roughly the speed of light.


Fun Facts About Our Sun

sun facts infographic

References:
- http://arxiv.org/pdf/gr-qc/9909087 (PDF)
- Murray, Carl; Stanley Dermott (1999). Solar System Dynamics. Cambridge UP. ISBN 0-521-57295-9.
- Hartle, JB (2003). Gravity: An Introduction to Einstein’s General Relativity. Addison-Wesley. p. 332.
- Taylor, Edwin F. and Wheeler, John Archibald, Spacetime Physics, 2nd edition, 1991, p. 12.


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