Telescopes from the Ground Up

The refracting telescope takes its final bow

In 1895, workers finished the largest achromatic refractor that would ever be created: the Yerkes telescope. George Ellery Hale, an American astronomer, convinced the Chicago tycoon Charles Tyson Yerkes to finance the telescope. Yerkes was a convicted embezzler with a reputation for dishonest deals, but he liked the idea of his name being attached to a famous telescope. He said he would pay whatever it took, but insisted repeatedly that the telescope had to be the largest in the world.

Get to the root of it

The telescope was built at Lake Geneva, Wis., near Chicago, 240 feet (73 meters) above sea level. This location was considered low, now that telescopes were being built on mountaintops to avoid some of the distorting effects of the Earth’s atmosphere. But the temperatures in the area could reach –20 degrees Fahrenheit in the winter, cold enough for the skies to be quite clear. Hale also felt mountaintop observatories were prone to storms, which could limit viewing.

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Great Refractors

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Map of Williams Bay, Wisconsin, where the Yerkes 40 inch refractor was located.
Image of the observatory staff at the base of the Yerkes 40 inch refractor.Enlarge picture
The Yerkes 40-inch Refractor
Year completed: 1895
Telescope type: Refractor
Light collector: Glass lenses
Lens diameter: 40 inches
(1.0 m)
Light observed: Visible
Discovery Highlights:
  • Measured changes in nearby star positions accurately enough to calculate their distances from Earth.