What is a Spectrograph

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WHAT IS A SPECTROGRAPH?

Spectrographs are devices used by astronomers to break up the light collected by a telescope into its various colors, or wavelengths. Usually a prism or diffraction grating is used for this purpose. The resultant "rainbow" is then recorded on film or electronically. The lines (either bright or dark) that inevitably show up in such spectra indicate the composition of the gases in the outer regions of the stars or planets being examined.

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