Yerkes Telescope 
DREISER: We're standing inside the 90-foot-diameter large dome that houses the Yerkes Observatory 40-inch refractor, largest lensed telescope in the world.
Richard Dreiser handles public outreach for the University of Chicago's Yerkes Observatory at Williams Bay, Wisconsin. It's home to an astronomical treasure: a 40-inch telescope built in the 1890s that's still the largest of its kind.
DREISER: There's a motor down below. I turn it on, and the entire dome begins to turn....George Hale learned about a couple of lenses that had been ordered, made of glass, from Mantois of Paris, and ground by Alvan Clark & Sons of Cambridgeport, Massachusetts, for the University of Southern California. But there was a bit of a depression in the late 1880s, early 1890s, and suddenly the lenses were available for $10,000. Hale decided that he wanted those lenses to make the biggest telescope in the world.
Hale worked with the University of Chicago to build the telescope. Today, though, it's been eclipsed by much larger reflectors, which use mirrors instead of lenses. And the weather at Williams Bay isn't the best for astronomical work. So the telescope is seldom used for research.
DREISER: And I'm stopping it now, and it coasts a little, and then stops.
But the telescope's work hasn't stopped. It's found a second career as a teaching tool for astronomy students, and for high school science teachers. That should keep this astronomical treasure going deep into the 21st century.
Script by Damond Benningfield, Copyright 2011