My understanding is that when an object moves away from you it increases the wavelength of the light presenting with a colour that is on the red side of the colourscale. Scientists also are able to determine what elements are present on planets based on the light it emits. How can they tell the difference?
I’m sorry for possibly using the incorrect terminology! Thanks in advance folks!
Edited the post because previously I had suggested that shorter wavelengths tended to the red side when in fact longer wavelengths tended to the red side of the colour spectrum.
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Because of the structure of each atoms, the way they absorb electromagnetic radiation is unique. You could think of it as a unique finger print of the atom. If we send light through let’s say a cloud of oxygen, and then we analyze the spectrum of that light, we will see dark lines where specific wavelength of light were absorbed by the oxygen. That’s the ”finger print” of the oxygen.
Now like you said when an object moves away from us it reduce the wavelength of the light toward the red. But this is a regular shift so the pattern remain the same.
Let’s use number to give an example. Let’s say that the wavelength absorbed by oxygen is 3 and the wavelength absorbed by hydrogen is 7. So if let light go through a cloud of water, on the other side you would see black line at 3 and 7.
But what if this light had a red shift, well then maybe you see black lines at 6 and 10. You can still recognize the pattern here, there is 4 of difference between the two. And to be sure, you can calculate the red shift is indeed 4 and now you know for sure that the light passed through oxygen and hydrogen.
Of course in reality spectroscopy is much more complex, but you get the idea.
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