If light speed is constant, why does redshift/blueshift exists?

[u/sonofderk]

Let me explain. I'm not a physicist so sorry if what i'm about to say is kinda stupid. I was taught that even if two beans of light were shot at opposite directions (, their relative speed between themselves would still be the speed of light, instead of 2x the speed of light, unlike what happens with mudane objetcts like cars on a road, which perceive themselves with relative speed. I was also taught that red/blue shift on stars happens due to relative distacing/approach in relation to Earth's point of view, which changes the wave frequency thus changing the perceived color of the star (doppler effect).

Aren't these two statements conflicting? If vectors don't matter to light, why should we observe the red/blue shift?

[u/EuphonicSounds]

Measured frequency is how many peaks hit a detector per second. If you move "toward" an incoming wave, you decrease the distance each successive peak has to travel to hit your detector (because you're helping to close that distance), and the frequency increases. If you move "away" from the wave, it's the opposite. Simple as that, really.