Spectrohelioscope

A spectrohelioscope is a type of solar telescope designed by George Ellery Hale in 1924 to allow the Sun to be viewed in a selected wavelength of light.

The basic spectrohelioscope is a complex machine that uses a spectroscope to scan the surface of the Sun.

The image from the objective lens is focused on a narrow slit revealing only a thin portion of the Sun's surface.

The slits are moved in unison to scan across the whole surface of the Sun giving a full image.

The spectroheliograph is a similar device, but images the Sun at a particular wavelength photographically and is still in use[1] in professional observatories.

Spectrohelioscope at Griffith Observatory , tuned to H-alpha
Schematic of typical spectrohelioscope. The two slits oscillate rapidly to allow a portion of the Sun to be seen in monochromatic light. Many variations are possible: collimation can be done with concave mirrors, dispersion can be achieved with glass prisms, and scanning can be achieved with fixed slits and spinning square prisms. Because they are large (usually more than 3 meters long) and delicate, spectrohelioscopes are usually fixed, with moving mirrors to track the Sun