Hi, I've run into a relativistic kinematics question that I'm not sure how to approach. The question states: "A source and a detector are spaced a certain angle [itex]\phi[/itex] apart on the edge of a rotating disk. The source emits radiation at frequency [itex]\omega[/itex] in it's instantaneous rest frame. What frequency is the radiation detected at? Hint: Little information is given because little is needed." I have no idea how to approach this. Since the detector and source are on a rotating disk, they are not connected by inertial frames. I want to say that their instantaneous rest frames are somhow connected, that is, the relative velocities of the frames are always the same. But where do I even begin? I thought perhaps I could work out where the detector would receive a photon emmited by the source, and maybe do a lorentz boost from the instantaneous rest frame of the source to a frame where both detector appear to be moving on the edge of the disk, then do a boost from that frame to the frame of the detector using the velocity of the detector at the time it would be received, but that seems complicated... what am I missing here?