The US government observatory in northwest Washington, DC. It was founded in 1844, taking over the astronomical work of the US Navy’s Depot of Charts and Instruments. It moved to its present site in 1893, absorbing the US Navy’s office of The Nautical Almanac. Its main instrument is a 26-inch (0.66-m) refractor, opened in 1873. Since 1955 the USNO has operated an observing station near Flagstaff, Arizona, at an altitude of 2315 m. The instruments here include the 1.55-m Kaj Strand astrometric reflector, opened in 1964; a 1-m reflector moved from Washington in 1955 and given a new mirror in 1969; and a 1.3-m wide-field telescope opened in 1999. USNO also jointly owns and operates the Navy Precision Optical Interferometer (NPOI) at Lowell Observatory.
http://www.usno.navy.mil/USNO Official observatory website.