Observatory Circle is a neighborhood in Northwest Washington, D.C., dominated by the grounds of the United States Naval Observatory (USNO) and the official residence of the vice president. There are approximately 500 households within the neighborhood. The main thoroughfare is Massachusetts Avenue, which, within the area of the Circle, is mainly lined with embassies.
The Naval Observatory itself is one of the oldest scientific agencies in the US. Its primary mission is to produce positioning, navigation and timing (PNT) data for the US Navy and US Department of Defense. Established by the order of the Secretary of the Navy, John Branch, in 1830, it was initially named the Depot of Charts and instruments. At the time of its building, it was far from the light pollution created by the then city center. Today, the observatory’s primary observation work is made near Flagstaff, Arizona. In addition to the PNT data, the Naval Observatory maintains the “Master Clock,” providing precise time to the GPS satellite constellation run by the US Air Force.