History
The Chicago Astronomical Society (CAS) was founded by scholars, and leaders in the arenas of business and politics in 1862 to advance the scientific knowledge of astronomy. The founders knew that a primary step in their mission was to build an observatory from which to conduct original research in the field. Inquires were made and the prime telescope maker in the United States was identified as Alvin Clark And Sons of Massachusetts. During negotiations Mr. Clark advised that he had completed and tested a lens of 18 ½ inches diameter – the largest apochromatic lens in the world—for the observatory of the University of Mississippi.
However, the outbreak of the Civil War meant that he could neither deliver the lens nor collect the selling price. Mr. Clark revealed that in testing the new lens, he had discovered a physical companion to the Star, Sirius, the first verified physical double star. The CAS team agreed on the spot to purchase the lens and have it shipped to Chicago.
Previously, arrangements were made by CAS to acquire vacant land at 35th Street and Cottage Grove Avenue on the “far south side of Chicago”, actually on the campus of the first University of Chicago. Contracts were let for the construction of an observatory building and for the crafting of an equatorial mount and optical tube to hold the Clark lens. Professor Hans ---, a renowned astronomer from Germany was hired to direct studies and research at the CAS observatory. Professor Hans made several discoveries of physical double stars. He began parallax studies of some of the brighter stars and was able to estimate their distances from Earth.
The First University of Chicago became insolvent and declared bankruptcy in the 1880s. The land was acquired by the state of Illinois. Most of that land was leased for 100 years to a developer to build up-scale housing on generous lots, and two separate oval subdivisions were built, Woodland and Groveland Park. The remaining State-owned land nearest 35th Street was declared a Memorial State Park to honor Frederick A. Douglas, the African-American scholar who frequently and successfully debated Abraham Lincoln. Douglas is buried on the site and an obelisk monument was raised. The monument can be seen by travelers on Lake Shore Drive as they pass 35th Street.
Meanwhile, CAS was forced to dismantle its observatory when the State acquired ownership of the land. Rather than retire or destroy this significant scientific tool, CAS donated the entire observatory to Northwestern University. The observatory building was reassembled and reinforced on the east side of the University campus. The telescope—no longer the largest refractor in the world—was recommissioned as the Dearborn Observatory. Now the CAS/Alvin Clark lens in mounted in a new Dearborn Observatory and is used by astronomy students. The observatory is open for public viewing one Friday each month.