Um, well, people have noticed that certain
objects in the sky that appear to be stars but
which move through the sky since as long as people
have looked up at the sky at night.
I believe it was Thomas Aquainus who created
his "crystal spheres" cosmology, in which the
moving "stars" were on different "spheres" from
the night sky background, and moved in orbit-like
motions, but he had them orbiting the Earth, not
Copernicus proposed that the spheres orbited
the sun and NOT the Earth.
Galileo actually made observations to
demonstrate it, though, as well as discovered that
Jupiter has a system of moons that orbit it just
as Jupiter itself and the other planets orbit the
Scientifically, I'd credit Galileo with the
discovery of planets as we now think of them.