The Theodor Jacobsen Observatory, built in 1895 and designed by Charles Willard Saunders, is the second-oldest structure on the University of Washington campus. The observatory was built using with coursed, split-faced Tenino sandstone left over from the construction of Denny Hall. Funding for the observatory also came from the Denny Hall building fund.
The building is named after Theodor Jacobsen (1901–2003), whose own astronomy research, beginning in the 1920s, coincided with the rise of astronomy as an academic discipline at the university. What began as a subject taught within the mathematics department eventually became its own department. Jacobsen served this new astronomy department from 1928 until his retirement in 1971.
The small, L-shaped, one-story, flat-roofed building features a two-story round tower with a sheet metal observatory dome. A wooden walkway with a railing encircles the second-floor exterior. True arches with voussoirs and a keystone top the narrow window openings and doorway and vaguely suggest classicism, yet the rusticated stonework is of different, seemingly haphazard sizes, providing the observatory with an almost medieval appearance.
The telescope inside the observatory dome features a six-inch Brashear objective lens on a Warner and Swasey equatorial mount, which rotates on three Civil War–era cannonballs. The telescope was ordered by professor Joseph Taylor, who taught the first astronomy class at the university in 1891 or 1892. Taylor received a grant of $3,000 from the university regents, of which $2,000 was spent on the (current) telescope and $1,000 on the original observatory (built on the original campus on Fourth Avenue and University Street in downtown Seattle). The telescope was moved to the present campus upon completion of the observatory building.
The observatory remains in use for public demonstrations, talks, tours, and events.