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spectrohelioscope(spek-troh-hee -lee-ŏ-skohp) The optical counterpart of the spectroheliograph, the principal difference being that both the entrance slit and secondary (viewing) slit are given a rapid oscillatory movement that enables the whole (or a part) of the Sun's disk to be seen by virtue of the observer's persistence of vision. Nowadays observation of the Sun in monochromatic light is routinely undertaken using automatic photographic patrol telescopes utilizing a narrow-band interference filter, but the spectrohelioscope is still used at some observatories and by serious amateurs, particularly for measuring the velocities of material Doppler-shifted away from the center of the hydrogen-alpha (Hα) line.
an astronomical spectroscopic instrument used for visual observation of the sun in monochromatic light.
The spectrohelioscope is a monochromator in which an image of the sun is projected on the plane of the entrance slit by means of a long-focus lens or mirror. The exit slit isolates a particular spectral line, usually the red hydrogen line Ha, of the solar spectrum. In the monochromatic light of the selected spectral line the observer sees the part of the solar image that is transmitted by the entrance slit of the instrument. When the two slits are vibrated synchronously at a sufficiently high frequency, persistence of vision permits observation of an area of the solar disk or of a region beyond the edge of the disk. Solar formations that emit or absorb in the given spectral line can be identified—for example, filaments and bright and dark flocculi on the solar disk, prominences at the sun’s limb, and chromospheric phenomena beyond the edge of the solar disk.
The first attempts at designing spectrohelioscopes were made in 1891 by H. Deslandres and G. E. Hale.