Thread: Frequency shift of photons emitted by rotating objects

The rough draft below shows the situation/Gedankenexperiment which I don´t understand.The (clockwise) rotating object (e.g. a galaxy) emits photons from identical atoms (say H2) at positions A and B, respectively. Photons A and B have the same wavelength/frequency. There´s an observer at a *constan*t distance from the rotating object who will see photon A blueshifted (relative to the emitted photon), and photon B redshifted.There´s no doubt about this, we have seen photos of the Andromeda Galaxy which clearly show this effect.But how can that be explained? There´s no relative motion between the photons (after emission) and the observer (in this Gedankenexperiment!).I´m obviously missing something fundamental here.