According to Copernicus, the retrograde motion for Mars must occur. Physics & Astronomy

at superior conjunction, when Mars lies on the far side of the Sun

at opposition, when the earth overtakes Mars and passes between Mars and the Sun

at inferior conjunction, when Mars laps the earth and passes between us and the Sun

at greatest elongation, when Mars can get up to 47 degrees from the Sun

at quadrature, when Mars lies exactly 90 degrees east or west of the Sun