Spectroheliograph

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

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.

It was developed independently by George Ellery Hale and Henri-Alexandre Deslandres in 1890 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.[1]

See also

References

  1. ↑ Information on observatories including Meudon spectroheliograph

External links

Wikisource has the text of the 1911 Encyclopædia Britannica article Spectroheliograph.
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