spectroheliograph

A spectroheliograph is an astronomical instrument used to study the Sun. It combines a spectrograph with a telescope to obtain images of the Sun's surface and atmosphere in light of a specific wavelength. This allows astronomers to isolate and observe phenomena occurring at particular temperatures and altitudes within the solar atmosphere.

The instrument works by first projecting an image of the Sun onto the slit of a spectrograph. As light from the Sun passes through the spectrograph, it is dispersed into its constituent wavelengths, creating a spectrum. A second slit, which moves across the dispersed spectrum, selects a narrow band of wavelengths. By synchronizing the movement of this second slit with the movement of the projected solar image, a complete image of the Sun can be built up in the light of the chosen wavelength.

Spectroheliographs are particularly useful for observing features like prominences, flares, and sunspots. By tuning the instrument to specific spectral lines, such as those of hydrogen or calcium, astronomers can map the distribution and evolution of these features. This provides insights into solar activity, magnetic fields, and the dynamics of the Sun's atmosphere. The first spectroheliograph was developed by George Ellery Hale in the late 19th century, revolutionizing the study of solar physics.