# Are there any examples where the transverse doppler effect is applied in astronomy?

Are there any astronomical examples where the transverse doppler effect(Horizontal doppler effect) is applied (Derives a meaningful result)?

• One key is that your examples deal with orbiting bodies, so that there is some other source of information about the motion besides the Doppler effect. For a body moving in free space, there is no way to take one input number (Doppler shift) and get two outputs (radial and transverse velocity). Also, the transverse Doppler shift is of order $(v/c)^2$, whereas the radial Doppler shift is of order $v/c$, so to get the transverse effect to be big enough not to be lost in the radial effect, you want big velocities. Hence your examples, which are highly relativistic systems.