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Observatories > Washington D.C. Observatory - USNO

U.S. Naval Observatory (Washington D.C.)


Credit : J.E.Arlot/USNO
The main building of the Naval Observatory

Credit : USNO
The 26-inch refractor

The naval Observatory has been founded in 1844 on a site close to the river Potomac and has been transferred to its present site, a hill at the north-west of the city of Washington D.C. in 1893. The observatory has several instruments on its grounds: astrographs including the large 26-inch refractor which has contributed to the astrometric observations of the solar system objects. In 1877, Asaph Hall discovered the satellites of Mars using this instrument.  


The Naval Observatory has the National Time Service, makes astrometric observations and has an ephemerides service, the Nautical Almanac Office. It has also an observing station in Flagstaff (Arizona) equipped with a Strand 61-inch astrometric telescope and a meridian transit circle still observing automatically each night the solar system objects for ephemerides purpose.