[Physics] Why does the earth revolve around the sun?


I want to know why the Earth rotates around the sun. Why doesn't it rotate around the moon or a different star?

Best Answer

It doesn't. All the planets and the Sun, along with asteroids and comets and multiple other objects all revolve around an effective center of mass known as the barycenter of the solar system. Because the mass of the Sun is so much larger than everything else, that barycenter is close to the Sun.

If you cconsider an isolated Earth-Sun system, the revolution would be around a point about 450 km from the center of the Sun. The Sun itself is about 696000 km in radius, so the Sun would be "wobbling" around, but the Earth is taking a very long trip around that point, from 150 Gm away. So, the primary appearance is that the Earth is travelling around the Sun. In reality, the Sun is moving, too, but due to the other planets, it's not a purely elliptical motion.

For the Earth-Moon system, the barycenter is about 4600 km from the center of the Earth, which is 6380 km in diameter. That's a much bigger "wobble" but the Moon is still a long distance away, 384000 km.

The Sun's mass is so larger that the Earth-Moon revolutionary system orbits the Sun together, but the Earth is also revolving around the Earth-Moon barycenter.