Telescopes from the Ground Up

Special instruments adorn a telescope designed to study the Sun

American astronomer George Ellery Hale wanted to study the Sun. To do that, he would have to attach the device he’d designed to photograph the Sun, a spectroheliograph, to the Yerkes refractor. After doing some calculations, Hale realized that if he used the Yerkes refractor, he would need a 10-foot spectroheliograph to get the best results. Attaching a 10-foot device to the telescope would have been time-consuming and made operation of the telescope clumsy.

Here comes the Sun

It was easier to build a new kind of telescope. The solar telescope would use a moveable mirror, called a coelostat (pronounced “seelostat”), to constantly reflect the Sun’s image into its instruments, even as the Sun moved across the sky. Because the mirror, not the telescope, would move to follow the Sun, the spectroheliograph could be fastened to stone or concrete supports.

Hale built his first solar telescope at the Yerkes Observatory near Chicago, but he barely had a chance to use it before a chance fire burned the telescope down. Hale was then given $10,000 by Helen Snow of Chicago, who asked that the new replacement telescope be named after George Washington Snow, her father.

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Map of Mt. Wilson, California, USA, where the Snow solar telescope is located.
Two images of the Snow solar telescope: an exterior of the observatory and a closeup of the heliostat.Enlarge picture
The Snow Solar Telescope
Year completed: 1904
Telescope type: Reflector
Light collector: Silver-coated glass mirror
Mirror diameter: 24 inches
(61 cm)
Light observed: Visible
Discovery Highlights:
  • With his solar telescopes, Hale showed that sunspots are associated with magnetic fields. They occur in pairs, one sunspot acting like the north pole of a magnet, the other acting like the south pole.