United States Naval Observatory

The United States Naval Observatory is a research center for astronomy and time measurement in Washington that operates atomic clocks and provides data for military and civilian purposes. The instruments include several telescopes that observe celestial bodies and serve to determine precise positions.

The facility began in 1830 as a depot for nautical charts and navigation instruments and moved to its current site in 1893 to escape growing light pollution. Since then, it has evolved into a center for modern timekeeping and celestial observation.

The name reflects the need to provide accurate time for navigation, which explains why the facility still operates precise clocks today. The library on site preserves historical books about the sky and ranks as the most important collection of its kind in the country.

Visitors must bring valid identification, and guided tours explain how the scientific equipment works. The site sits in a quiet neighborhood and is accessible only by prior arrangement.

The grounds hold Number One Observatory Circle, which has served as the official residence of the Vice President since 1974. Few know that the facility also supports international coordination for defining the second.

Location: Washington, D.C.

Inception: 1842

Official opening: 1893

Accessibility: Wheelchair accessible

Address: 3450 Massachusetts Ave NW, Washington, DC 20392

Website: https://cnmoc.usff.navy.mil/usno

GPS coordinates: 38.92139,-77.06694

Latest update: December 12, 2025 22:15