The Great Equatorial Building/26-Inch Telescope House.

ID: 5512 ~ Source: National Register Nomination Form. ~ Creator: Haley Schriber, John Milner Associates Preservation, Arlington, Virginia and John Twomey, U.S. Secret Service, Washington, D.C. ~ Date: July 2020.
This file appears in: United States Naval Observatory (USNO) Historic District: The USNO is the only American institution devoted to positional astronomy and timekeeping.

Looking northwest towards south elevation of Building 2 (from nomination form).

This file appears in: United States Naval Observatory (USNO) Historic District: The USNO is the only American institution devoted to positional astronomy and timekeeping.