Why is earth moving in an orbit around the sun and why is the sun not moving in an orbit around thae earth?

Answer 1

The fact is that whenever you have two bodies gravitationally coupled with

orbital motion going on, both bodies are orbiting their common center of mass.

That's the point where the pivot would have to be if the two bodies were on

opposite ends of a see-saw. And just as on a see-saw, if one body is more

massive than the other one, then the common center is closer to that one.

In the case of the sun and Earth, the sun is about 333 thousand times as

massive as the Earth, so the Earth is about 333 thousand times farther from

their common center of mass. That puts their common center of mass about

280 miles from the center of the sun, or about 0.06% of the way out from the

sun's center to its surface, and that's the point around which the sun and Earth

mutually revolve.

Which is why, if you were out in space watching the whole thing, you wouldn't

even notice the sun wiggling, and you'd swear that the sun is staying solidly in

one place, and the Earth is revolving around it.

(Remember that the sun also does a little wiggle for every other planet, comet,

and asteroid in solar orbit.)