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A spectrograph is an instrument that separates incoming light according to its wavelength and records the resulting spectrum in some detector. It is a type of spectrometer and superseded the spectroscope for scientific applications.

In astronomy, spectrographs are widely used. These are installed at the focus of a telescope which may be either in a ground-based observatory or in a spacecraft.

The first spectrographs used photographic paper as the detector. The star spectral classification and discovery of the main sequence, Hubble's law and the Hubble sequence were all made with spectrographs that used photographic paper.

More recent spectrographs use electronic detectors, such as CCDs which can be used for both visible and UV light. The exact choice of detector depends on the wavelengths of light to be recorded.