The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States. It is located in Washington, D.C.. It is one of the very few observatories located in an urban area (when it was initially constructed, it was far from the light pollution generated by the then-smaller city center).
Established in 1830 as the Depot of Charts and Instruments, the observatory's primary mission was to care for the U.S. Navy's chronometers, charts and other navigational equipment. It calibrated ships' chronometers by timing the transit of stars across the meridian. Initially located downtown in Foggy Bottom (near the Lincoln Memorial and the Kennedy Center), the observatory moved to upper Northwest Washington in 1893, where it is sited on top of a hill overlooking Massachusetts Avenue , amidst perfectly circular grounds.
Today, the U.S. Naval Observatory is the preeminent authority in the areas of time-keeping and celestial observation. It determines and distributes the timing and astronomical data required for accurate navigation and fundamental astronomy, but perhaps it is best known to the general public for its highly accurate ensemble of atomic clocks.
Since 1974 Number One Observatory Circle, a house situated in the grounds of the observatory (formerly the residence of its superintendent), has been the official residence of the Vice President of the United States.
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