velocity of the observer? What? The concept of red-shift seems to suggest, that although the SPEED of light is constant, its wavelength and frequency are not. What does this mean in terms of E=hf? The energy the photon possesses increases (in the observer's frame).. IF the observer is moving at a velocity towards it? Sure, if you move AWAY at a certain speed from the source of the light you will get red shift, but what if you move towards it? Will you get a blue shift? How fast would you need to be moving towards the light source to see 'gamma shift'. (IS this speed faster than the speed of light?) And if the kind of radiation you experience is dependent on your velocity towards or away from the source, how would we determine a light source's "True-wavelength". Is there such thing?