Yerkes Observatory, in Williams Bay, Wisconsin, houses the largest refracting telescope ever built for astronomical research, with a main lens that's 40 inches (1.02 meters) in diameter.

B-W opens the observatory once a month during the academic year, except in December, for such lectures and viewing. The observatory, located on the campus' northern section, was built in 1940.

The original instrument to occupy the 25-foot diameter dome was the 10.5-inch Bausch refracting telescope (f/15.5) installed in the brand new observatory in 1953. Bausch & Lomb Company gave the ...