Spectroheliograph

Spectroheliograph, important part of the equipment used in astronomy to photograph features of the Sun, such as the photosphere (the inner layer of hot gases nearest to the Sun's surface) and the chromosphere (the outer cooler layer). The spectroheliograph, in conjunction with a telescope, photographs the Sun in monochromatic light—that is, light of a single, almost pure colour. It can record the radiation of a single spectral line produced by a chemical element such as hydrogen or calcium (see Spectroscopy). A composite picture of the Sun showing the distribution of that element is built up on the photographic plate as the Sun traverses the sky.

The spectroheliograph was invented independently by two astronomers in the early 1890s: the American George Hale and the Frenchman Henri-Alexandre Deslandres. Hale also played an important part in the development of the spectrohelioscope; this instrument allows visual observation of solar phenomena by creating persistence of vision when the slits in the instrument are vibrated synchronously at high frequency.