This follows from Newton's 2nd law. Neither the Earth nor the Sun is at the center of the universe . The other part of Kepler's first law was also modified by Newton. Planets do not move in perfect ellipses. Because Newton explained gravity, these perturbations are entirely predictable.
Perturbations are usually pretty small, undetectable with the naked eye.
But astronomers can easily detect these deviations with telescopes. Astronomers found the planet Uranus to be deviating from its expected orbit, even when perturbations of the other planets were included. It was guessed that an 8th, unknown, planet might be the source of these perturbations. Astronomers deduced where the 8th planet would have to be to cause these perturbations and, sure enough, there was Neptune. Discovered in 1846.