An angular position sensor can include a magnetic device from which a magnetic field emanates, and multiple magnetometers, whereby each magnetometer senses a varying strength of the magnetic field due to relative rotation between components of a well tool. A method of determining an azimuthal position of a shaft which rotates relative to an outer housing can include securing a selected one of at least one magnetic device and at least one magnetometer to the shaft, securing the other of the magnetic device and the magnetometer to the outer housing, a fluid motor rotating the shaft relative to the outer housing in the well, and the magnetometer sensing a varying strength of a magnetic field emanating from the magnetic device as the shaft rotates relative to the housing.