What does the Doppler Effect tell astronomers about the universe?
LOTS AND LOTS OF STUFF!!!
You have probably heard that the universe is expanding. We know this thanks to the Doppler effect. Like with a car moving away and having it's pitch changed, galaxies are also affected by the Doppler effect. As a galaxy moves away from or towards us, the electromagnetic radiation it emits changes in wavelength. A Galaxy moving away will have its radiation shifted towards the red end of the spectrum, whilst one moving towards us will shift towards the blue end.
How do we find out about these wavelengths? Using Spectroscopy. Different elements emit and absorb different wavelengths of radiation - including the elements making up a body in the universe.
By comparing the emission and absorption spectra of celestial bodies and objects to the spectra of known elements, we can then see how much the absorption/emission lines have shifted to then calculate the speed at which the object is moving.
There is a lot more to talk about with this topic, so if you would like to know more give me a message - I'm afraid I'm off to bed now!
Hope this helps!