Splitting the light from a star or other celestial object into the bands and lines of a spectrum gives astronomers clues about how hot the body is, whether it is advancing or retreating, whether it is spinning, whether it is dense or thin, what it is made of. Unfortunately, for technical reasons, not all the light of a celestial image can be crammed into the spectrograph.
To get a clear spectrum it is necessary to work with a very narrow band of light; but, because of atmospheric distortion, the image comes in as a diffuse,...
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