Can we be 100 % sure that the earth is orbiting around the sun and not the opposite?
There are a number of observations that prove Earth moves around the Sun. Astronomers have found that relatively nearby stars appear to move horizontally back and forth slightly over a year’s time. This effect is due to a phenomenon called parallax which in turn results from Earth’s movement around the Sun. Also Earth’s measured movement through the cosmic microwave background radiation is consistent with our orbit around the Sun. This website has a more complete discussion about proofs of Earth’s orbit around the Sun — http://curious.astro.cornell.
