> The observed frequency of a light beam is NOT intrinsic to the light
> beam, but is a relationship among the source of the light beam, the
> trajectory of the light beam, the geometry along the trajectory, and the
> receiver.
>
> It is easier to think about the time interval between successive crests
> of the light (i.e. its period), rather than its frequency.

The time interval between two successive crests surely is dependent on the
motion of the receiver relative to these crests. So from that we can
conclude that red or blue shift is a function of the absolute motion of the
receiver.

Ken Seto