How do we know that galaxies are moving away?

The answers by Alec and Daniel are bang on. Just to add my 2 cents to the question; it's really interesting how we got to the red shifts and blue shifts. When we aim a prism towards the sun, we get the whole spectrum. read more

The answers by Alec and Daniel are bang on. Just to add my 2 cents to the question; it’s really interesting how we got to the red shifts and blue shifts. When we aim a prism towards the sun, we get the whole spectrum. read more

But how do we know that they are moving away from each other (which is what should happen if this is the effect of an expanding Universe). I keep reading this claim but I have not been able to find any observational data that back it up. read more

But we won’t bring that in to make things even more complex. As we look out into the Universe, we see galaxies moving away from us faster and faster. The more distant a galaxy is, the more quickly it’s moving away. read more