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The spectroheliograph is an instrument used in astronomy. It captures a photographic image of the Sun at a single wavelength of light, a monochromatic image. The wavelength is usually chosen to coincide with a spectral wavelength of one of the chemical elements present in the Sun.
It was developed independently by George Ellery Hale and Henri-Alexandre Deslandres in 1890 and further refined in 1932 by R. R. McMath to take motion pictures.
The instrument comprises a prism or diffraction grating, together with 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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