spase://SMWG/Instrument/EvansSolarFacility/Spectroheliograph

The National Solar Observatory's Evans Solar Facility
is at Sacramento Peak, Sunspot, New Mexico. ESF is two telescopes in one,
both tracking the solar cycle. A 16" coronagraphic telescope maps magnetic
changes in the Sun's outer atmosphere. A special set of 12" coelostat
optics "squints" so the Sun appears as a pinpoint, allowing an "apples
and apples" comparison with the cycles of distant stars. The
spectroheliograph is basically a specially designed camera that scans
across an image of the sun, while letting only light from one particular
color fall onto a light detector, such as film. It is possible for the
spectroheliograph to pass light produced from the hydrogen or calcium
atoms of the sun, for example. Because of the temperature and density
variation with height in the solar atmosphere, and the resulting offset
in differents types of atoms, the solar atmospheric structure at
different heights can can be observed. See http://nsosp.nso.edu/esf/