Former Wisconsin governor and prosperous businessman Cadwallader Washburn began building the observatory in 1878 and presented it as a gift to the university and state of Wisconsin—the university’s first scientific research facility. Gov. Washburn died in 1882, the year that it was completed and fully equipped. The observatory was built on land ancestral to the Ho-Chunk, a place their nation has called Teejop (day-JOPE) since time immemorial. Much more recently, our continuous tradition of public nights began in April 1881, instituted by observatory director Edward Holden. To this day, thousands of visitors every year enjoy the view of the night sky and learn from Washburn’s generous gift atop beautiful Observatory Hill, following traditions of our ancestors for over 10,000 years.
Washburn’s observatory started with the main building, including central dome and west-wing transit house, and a large extension of the east wing housing a library, shop, and rooms for computing and sleeping. Two primary research instruments: a 15.6-inch equatorial refractor and a 4.8-inch meridian circle, were both purchased by Gov. Washburn, who had specified that the equatorial should be “equal or superior to” Harvard’s, thus declaring his intentions of creating a significant research institution. He also obtained legislation allocating a set amount of state funding to support astronomers, who would be employees of the University of Wisconsin. This formula of private donation, dependable state support, and expert university operation proved stable and productive.
Ancillary structures, both planned and begun by director James Watson and finished by Gov. Washburn, included a Student Observatory and a Solar Observatory. The Solar Observatory played a part in Watson’s unsuccessful search for the planet Vulcan, and the Student Observatory housed the 6-inch Clark Equatorial refractor that originally belonged to famed double star observer S. W. Burnham.
The 15.6-inch telescope is nearly original as installed in 1879. The parts painted light blue are original, while the dark blue mounting and the gray pier replaced the original mounting and pier in 1933. The telescope was made by the firm of Alvan Clark & Sons in Massachusetts, who made some of the largest and most famous research refractors in the world.
With its 15.6-inch diameter objective lens, it was the 3rd largest in North America when it became operational in January 1879. (The largest refracting telescope in the world, dating from 1896, is also in Wisconsin. That is the 40-inch Clark refractor of Yerkes Observatory in Williams Bay.)
The original observatory building housed the instruments, workshops, offices, and Woodman Astronomical Library until the Astronomy Dept. relocated to the east wing of Sterling Hall in 1959. Observational research was moved to the new Pine Bluff Observatory about 15 miles west of Madison. Since that time, the 15.6-inch equatorial telescope is devoted to outreach and education while Washburn Observatory has served administrative, office, and classroom purposes. The observatory is currently home to the Letters & Science Honors Program of the University of Wisconsin-Madison.
During its most active and productive era, in the first half of the 20th Century, a great deal of very important research was done at Washburn Observatory. Measurements of the motions of binary stars and stellar parallaxes were an early specialty. Astronomical photoelectric photometry, essential to modern astrophysics, was developed at Washburn beginning in the 1920s. That work resulted in very important discoveries on the nature of stars, star clusters, interstellar matter, and even the discovery of the true size and spiral structure of our Milky Way Galaxy.
Learn More about Washburn Observatory
To learn more about the history of Washburn Observatory and its scientific legacies, see the book by James Lattis and Kelly Tyrrell, Chasing the Stars: How the Astronomers of Observatory Hill Transformed Our Understanding of the Universe (Wisconsin Historical Society Press, 2024).