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This is a question that I've had for years but because astrophysics and cosmology are down in the list of my interests, I constantly forget and remember the question.
My question is, how do we know there is shift(red or blue) in the spectrum of the light coming from a star? Because for understanding this, we should somehow have access to the spectrum of the light immediately emitted by the star, which I don't know how that is possible.
Thanks
My question is, how do we know there is shift(red or blue) in the spectrum of the light coming from a star? Because for understanding this, we should somehow have access to the spectrum of the light immediately emitted by the star, which I don't know how that is possible.
Thanks