Definitions

spectroheliograph

spectroheliograph

[spek-troh-hee-lee-uh-graf, -grahf]
spectroheliograph, device for photographing the surface of the sun in a single wavelength of light, usually one corresponding to a chief element contained in the sun, e.g., hydrogen or calcium; the resulting photograph is called a spectroheliogram. The spectroheliograph was invented in 1890 independently by G. Hale and by H. Deslandres and modernized (1932) by R. R. McMath to take motion pictures. In operation, the instrument is preset by means of a prism or grating and a narrow slit that passes only one wavelength of light to a photographic plate or digital detector; the image of the sun is then moved slowly or stepwise across the entrance slit until the entire disk of the sun has been photographed. See spectrum.
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 Robert 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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