&gt;the ad lectorum (to the reader) that he added to the front of Copernicus’ De revolutionibus that one could regard the heliocentric hypothesis as a mere mathematical model and not necessarily a true representation of the cosmos<p>But choice of reference frame <i>is</i> arbitrary. Modeling the solar system or even the universe with Earth fixed at the center is just as valid as with the sun fixed at the center. Even today the ad lectorum is not wrong per se!