The spectroheliograph is an instrument used in astronomy which captures a photographic image of the Sun at a single wavelength of light, a monochromatic image. The wavelength is usually chosen to coincide with an spectral wavelength of one of the chemical elements present in the Sun.
The instrument comprises a prism or diffraction grating and a narrow slit that passes a single wavelength (a monochromator). The light is focused onto a photographic medium and the slit is moved across the disk of the Sun to form a complete image.
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