The spectroscope (upper diagram) is used to analyze light. Light from a telescope is passed through a fine vertical line in a plate (1). A lens (2) concentrates the rays onto a prism (3), which splits them into a spectrum. A second prism (4) is positioned so that the spectrum is widened even further after passing through it. The wide spectrum is then focused by a lens (5) onto a screen (6). The screen may be replaced by a recording apparatus; this instrument is called s spectrograph. The lower diagram shows a typical emission spectrum from various elements. The colored lines become dark when superimposed on the continuous spectrum giving Fraunhofer lines.

A spectroscope is an instrument used for splitting light, or other electromagnetic radiation, into its component wavelengths – a spectrum – for visual observation. Spectroscopes are used in astronomy to study the light from stars and other celestial objects, and in chemistry to detect the presence of traces of various elements in samples that are too small analyze by other means.

The light entering a spectroscope is collimated into a narrow beam by means of a slit and lens. The beam then passes through a prism or a diffraction grating so that it is dispersed into a spectrum. Combined with the grating or prism is a scale from which the spectral wavelengths may be read directly through the telescope that magnifies the spectrum.


Astronomical spectroscopes are known as spectrographs or spectrometers. Strictly, a spectrograph is a spectroscope equipped with a camera for recording a permanent record of a spectrum, whereas a spectrometer incorporates devices for accurately measuring the wavelengths and intensities of the spectral lines. See also spectroscopy.