United States Naval Observatory

Located in Northwest Washington, D.C., the United States Naval Observatory (USNO) opened in 1844. It operates to strengthen national security and critical infrastructure by serving as the Department of Defense’s (DoD) authoritative source for the positions and motion of celestial bodies, motions of the Earth, and precise time—the official time source for the DoD. The official residence of the U.S vice president is also located on the grounds of the USNO.

While the USS District of Columbia is the first Navy warship to be named in honor of Washington, D.C., the Navy has deep roots in the District. Did you know that starting in 1845, the U.S. Naval Observatory made sure that local Washingtonians were always on time?

At the request of the Secretary of the Navy, the U.S. Naval Observatory installed a "time ball" atop the 9.6-inch telescope dome. The time ball was dropped daily (except Sunday) precisely at local mean solar noon, enabling the inhabitants of Washington to set their timepieces.   Ships in the Potomac River could also check the rates of their chronometers before putting to sea.

The Observatory's Time Service was initiated in 1865.  A time signal was transmitted via telegraph lines to the Navy Department, and also activated the bells in all of the Washington fire stations at 0700, 1200, and 1800 every day. This service was later extended via Western Union telegraph lines to provide accurate time to railroads across the nation.

The Observatory also participated in a program of determining longitude by comparing local time with that telegraphed from a clock at another fixed observatory, and thus exchanged time signals with other observatories and with the Coast Survey field parties. 

Thanks to our partners at the Naval History and Heritage Command and the U.S. Naval Observatory for this Quarter’s DC History Moment.