Spectroheliograph

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 a spectral wavelength of one of the chemical elements present in the Sun.

Solar flare photographed in the light of ionized helium, using the extreme-ultraviolet spectroheliograph of the U.S. Naval Research Laboratory.

It was developed independently by George Ellery Hale and Henri-Alexandre Deslandres in the 1890s[1] and further refined in 1932 by Robert R. McMath to take motion pictures.

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.

It is now possible to make a filter that transmits a narrow band of wavelengths which produces a similar image, but spectroheliographs remain in use.[2]

See also

References
  1. Michard, R (2008). "Deslandres, Henri." Complete Dictionary of Scientific Biography. Detroit: Charles Scribner's Sons. pp. 68–70. Retrieved 13 June 2015.
  2. Information on observatories including Meudon spectroheliograph


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