Dearborn Observatory on Northwestern University’s Evanston campus traces its significance to the Dearborn eighteen-and-a-half-inch refractor, one of the largest telescopes of its time. Built around a lens made by Alvan Clark and Sons, the instrument first gained fame on January 31, 1862, when Alvan Graham Clark observed Sirius B while testing it. After serving the old University of Chicago, the telescope was moved to Northwestern in the late 1880s under a partnership with the Chicago Astronomical Society. The observatory was later relocated on campus, transferred fully to Northwestern in 1930, and remains active for teaching and free public observation.