That's my point. If the speed of light is constant, then whether you're moving away from the sun at a million miles an hour, or towards it at thousand - wouldn't the light still reach you at c and therefore how can you catch upto it or move away from it at a different speed, to give red or blue shift?
I understansd how it works with sound waves and sonic booms because you *can* go faster of slower than sound does. But you can't go faster or slower than light does, can you? Even if you're totally stationary, light is still approaching you at light speed.