Democritus came up with a theory that there are indivisible atoms of matter. Heraclitus that fire was the first principle of all things, and Thales that it was water. These philosophers were philosophising; what they were not doing was science as we understand it. They were throwing up ideas and seeing what might stick, but without what we would consider empirical evidence. If Democritus and not Thales turns out to have been right, it was entirely by accident.
Same with Aristarchus and Copernicus. Even if Copernicus had read up on Aristarchus (e.g. Aristarchus and Copernicus; see also Gingerich, O. “Did Copernicus Owe a Debt to Aristarchus?” Journal for the History of Astronomy, Vol.16, NO.1/FEB, P. 37, 1985, cited in Wikipedia), Copernicus based his work on observational data (De revolutionibus orbium coelestium). The real work cementing it all, as Wade Schmaltz points out, came later with Galileo and Kepler; yet even what Copernicus did was in a different paradigm from the idle ideations of the ancients.