spectroheliograph

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 .

spectroheliograph An instrument for photographing the Sun at the wavelength of a strong Fraunhofer line. An image of the Sun produced by a telescope is focused on to a primary slit, and light from this slit passes to a grating or prism. The dispersed light so formed is then intercepted by a secondary slit positioned at a desired wavelength (e.g. a part of the Hα line) and a photographic plate is placed behind this slit. The primary slit is then moved across the image of the Sun and the secondary slit moved to maintain its spectral location, producing a spectroheliogram on the photographic plate or CCD.

spectrohelioscope An instrument with which the Sun can be observed visually at the wavelength of a particular spectral line. The principle is very similar to that of the spectroheliograph, except that the primary and secondary slits are moved rapidly back and forth over the solar image, so rapidly that the eye is unaware of the motion.