since different gases give different color when burning, how can we know that the red colour we obtained is not just the actual color of gases burning, but rather a red shift?
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Gasses don’t burn in stars and since 75 % of mass in any galaxy is hydrogen, we know what hydrogen fusion spectrum needs to be.
Gases produce very very specific bands as plasma. For instance, hydrogen produces 656.46nm light. We call this H-alpha. We can calibrate our redshift predictions based upon how much these lines shift.
Also, it’s not ‘burning’, just very hot.
The color is different but not completely random. Each element emits a very specific spectrum of light. To not go into exact numbers, we can say that hydrogen emits light at wavelengths A, B and C. When we look at another galaxy, we see light with similar but shifted wavelengths: A-x, B-x and C-x. The only way to achieve it is to get “normal” light from hydrogen through the red shift. And we can even measure that shift.
Red shift and blue shift is the title we have given to what can happen to the expected colour spectrum indication when we look at a far away object.
If we expect X, but get X+Y, we know that either we have issues with measuring, or something else happened.
We have since ruled out the possibility of measuring being flawed and are left with only the possibility that what should be X, is shown as X+Y, and the reason for that is that these objects are moving away or towards us.
Elements release very specific wavelengths of light. This is directly tied to quantum mechanics and is very predictable. Stars have a fingerprint that is defined by the elements they’re made up of and have a distinct pattern. If you’re looking for the line for hydrogen and it’s not there, you know that it’s either being red or blue shifted. Or you’re looking at a star without hydrogen which in of itself would be interesting. Combined with other elements and expected wavelengths of light scientists can figure out pretty easily if it’s being red or blue shifted.
Keep in mind that is not the ONLY way to do it. Scientists usually use multiple methods to confirm and they can involve things like behaviors of certain types of stars.
If you pass the light from an object through a prism and inspect it closely, there will not be a smooth, continuous rainbow. There will be gaps in the colors.
These gaps are caused by the presence of certain atoms and molecules, either in the thing emitting the light itself, or in obstacles between us and the thing of interest.
Each atom or molecule takes a very specific “bite” out of the rainbow. Like a unique signature. We know what these signatures look like and where on the rainbow they are supposed to be.
If you notice a signature of an atom or molecule that has the right shape, but isn’t bitten out of the correct color, that’s how you know it’s been shifted, and you can “unshift” all the data back to where it should be to derive the original color. If it’s exactly where you expect it to be, then you’re already seeing the object in true color and no shift is necessary.
Occam’s razor.
Gases give of specific frequencies of light and not he full spectrum. To the naked eye it just looks red or grenn, but if you break that light up to see the spectrum there are only a few specific wavelengths present. This light is caused by electrons hopping around in the atoms electron cloud.
When we look at distant galaxies we see the same spectrum but it’s shifted-almost always in the red direction. That tells us either
1. The galaxy is made of the same stuff we see here on Earth that’s emitting light in ways we understand. It’s just moving and making that light redshifted
2. The galaxy is made of some new unknown substances that is behaving in some unknown ways that only appears to mimic a collection of gases we know all having the same motion to shift the light.
That’s where Occam kicks in and we say the second explanation has more complexity because it need an entirely new substance in addition to our familiar matter as well as all the new ways it interacts to emit light while the first theory say that stuff we already know is doing stuff we already know it does. So we go with theory #1.
The Doppler Effect is a well studied and understood phenomena. Basically the motion of an object affects how we perceive things from it. Wavelengths appear to be higher when the object is moving towards you and and when something is moving away. You experience with sound wave: the pitch of the sound of a car is different when it is moving towards or away from you.
Since materials produce and reflect very specific frequencies of light even when they are in high energy & gaseous states, we can use that as a reference points to determine how fast an object is moving. Even in the sun, there are several different specific frequencies in the light we can see that tell us what materials are inside it. It’s not a case of there just being one wavelength being produced, but several.
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