page_title: Yerkes Observatory
section_title: The 40-inch aperture refractor
hierarchical_section_title: Yerkes Observatory / Telescopes / The 40-inch aperture refractor
caption_attribution_description: English: Rumford spectroheliograph attached to the Yerkes telescope
context_page_description: Yerkes Observatory is an astronomical observatory located in Williams Bay, Wisconsin, U.S.A. It was operated by the University of Chicago Department of Astronomy and Astrophysics from its founding in 1897 to 2020. Ownership was transferred to the non-profit Yerkes Future Foundation in May, 2020.
  The observatory, sometimes called "the birthplace of modern astrophysics", was founded in 1892 by astronomer George Ellery Hale and financed by businessman Charles T. Yerkes.
  It represented a shift in the thinking about observatories, from their being mere housing for telescopes and observers, to the early-20th-century concept of observation equipment integrated with laboratory space for physics and chemistry analysis.
  The observatory's main dome houses a 40-inch diameter doublet lens refracting telescope, the largest refractor ever successfully used for astronomy. Two smaller domes house 40 in and 24 in reflecting telescopes. There are several smaller telescopes - some permanently mounted - that are primarily used for educational purposes. The observatory also holds a collection of over 170,000 photographic plates.
context_section_description: The glass blanks for what would become Yerkes Great Refractor were made in Paris, France by Mantois and delivered to Alvan Clark & Sons in Massachusetts where they were completed. Clark then made what would be the largest telescope lens ever crafted and this was mounted to an Equatorial mount made by Warner & Swasey for the observatory. The telescope had an aperture of 40 inches (~102 cm) and focal length of 19.3 meters. The lens, an achromatic doublet which has two sections to reduce chromatic aberration, weighed 225 kilograms, and was the last big lens made by Clark before he died in 1897. Glass lens telescopes had a good reputation compared to speculum metal and silver on glass mirror telescopes, which had not quite proven themselves in the 1890s. For example, the Leviathan of Parsonstown was a 1.8 meter telescope with a speculum metal mirror, but getting good astronomical results from this technology could be difficult, and another large telescope of this period was the Great Melbourne Telescope in Australia, also a metal mirror telescope.
  Some of the instruments for the 40-inch refractor (circa 1890s):
  Filar Micrometer
  Solar spectrograph
  Spectroheliograph
  Stellar spectrograph
  Photoheliograph
  The 40-inch refractor was modernized in the late 1960s with electronics of the period. The telescope was painted, the manual controls were removed, and electric operations were added at this time. This included nixie tube displays for its operation.
caption: Spectroheliograph instrument on the 40-inch refractor in 1904
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