OBJECT HISTORY: Yerkes Telescope

The 40-inch refracting telescope at Yerkes Observatory in Williams Bay, Wisconsin, contains the world’s largest refracting lenses. Built in 1895, the telescope contains two lenses, one made of crown glass, and one made of flint glass. The lenses are each 40 inches in diameter, weigh 500 pounds, and have a 62-foot focal length. The telescope and observatory…