For example, the further a galaxy is from us, the more red it is.
In: Planetary Science
This is the Doppler Effect. We experience it with sound every day (if you ever watch Formula 1, listen to how the engine noise from the cars changes as they approach, pass and move away from the camera and microphones; frequency increases as they get closer and decreases as they pass – we hear the same with sirens from emergency vehicles as they approach and pass us). Basically if something approaches you, waves it emits get bunched together: they become more frequent i.e. higher frequency. Waves from an object moving away from you are spread out – less frequent, lower frequency.
We can experience this because sound moves comparatively slowly (around 330 metres per second) so a vehicle moving at 10 metres per second will cause a noticeable change in frequency of sound emitted. Light moves at three hundred million metres per second; way too fast for movement on earth to affect frequencies – though I did get a chuckle at a bumper sticker with red lettering saying “If this appears blue then you’re travelling too fast”.
Blue light has a higher frequency than red light so looking at light from an object moving towards you, it will appear “blue shifted”, shorter wavelength. An object moving away from you is conversely “red shifted”. We can use this phenomenon to show the universe is expanding and that more distant objects are more red shifted – the further away they are, the faster they’re moving away from us.
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