discovered the
moons of Mars in 1877; the telescope is shown at its modern Northwest DC location. President
John Quincy Adams, who in 1825 signed the bill for the creation of a national observatory just before leaving presidential office, had intended for it to be called the National Observatory. The names "National Observatory" and "Naval Observatory" were both used for 10 years, until the Secretary of the Navy officially adopted the latter. Adams had made protracted efforts to bring astronomy to a national level. He spent many nights at the observatory, watching and charting the stars, which had always been one of his interests. Established by order of the
United States Secretary of the Navy John Branch on 6 December 1830 as the Depot of Charts and Instruments, the Observatory rose from humble beginnings: Placed under the command of Lieutenant
Louis M. Goldsborough, with an annual budget of $330; its primary function was the restoration, repair, and rating of navigational instruments.
Old Naval Observatory It was established as a national observatory in 1842 by federal law and a Congressional appropriation of $25,000. Lt.
J.M. Gilliss was put in charge of "obtaining the instruments needed and books." Lt. Gilliss visited the principal observatories of Europe with the mission to purchase telescopes and other scientific devices, and books. The observatory's primary mission was to care for the
United States Navy's
marine chronometers, charts, and other navigational equipment. It
calibrated ships' chronometers by timing the
transit of
stars across the
meridian. It opened in 1844 in
Foggy Bottom, north of the site of the
Lincoln Memorial and west of the
White House. In 1893, the observatory moved to its current location in Northwest Washington, D.C. located on a 2000 foot circle of land atop "Observatory Hill", overlooking
Massachusetts Avenue. In 2017, the facilities were listed on the
National Register of Historic Places.
The time ball The first superintendent was Navy Commander
M.F. Maury. Maury had the world's first
vulcanized time ball, created to his specifications by
Charles Goodyear for the U.S. Observatory. Placed into service in 1845, it was the first time ball in the United States and the 12th in the world. Maury kept accurate time by the stars and planets. The time ball was dropped every day except Sunday, precisely at the astronomically defined moment of
mean solar noon; this enabled all ships and civilians within sight to know the exact time. By the end of the American Civil War, the Observatory's clocks were linked via
telegraph to ring the alarm bells in all of the Washington, D.C. firehouses three times a day. The USNO held a one-off time-ball re-enactment for the year-2000 celebration.
Nautical Almanac Office In 1849, the Nautical Almanac Office (NAO) was established in
Cambridge, Massachusetts as a separate organization. In 1866, it was moved to
Washington, D.C., operating near Fort Myer. It relocated to the U.S. Naval Observatory grounds in 1893. The library includes a large collection of rare physics and astronomy books from the past millennium.
Measuring the astronomical unit An early scientific duty assigned to the Observatory was the U.S. contribution to the definition of the
Astronomical Unit, or the , which defines a standard
mean distance between the Sun and the Earth. This was conducted under the auspices of the congressionally-funded U.S. Transit of Venus Commission. The astronomical measurements taken of the
transit of Venus by a number of countries since 1639 resulted in a progressively more accurate definition of the . Relying strongly on photographic methods, the naval observers returned 350
photographic plates in 1874, and 1,380 measurable plates in 1882. The results of the surveys conducted simultaneously from several locations around the world (for each of the two transits) produced a final value of the
solar parallax, after adjustments, of 8.809″, with a probable error of 0.0059″, yielding a U.S.-determined Earth-Sun distance of , with a probable error of . The calculated distance was a significant improvement over several previous estimates.
The 26 inch refractor and 40 inch reflector The telescope used for the discovery of the
Moons of Mars was the 26 inch (66 cm)
refractor telescope, then located at
Foggy Bottom, Washington, DC. In 1893 it was moved to its Northwest DC location. In 1934, the largest optical telescope installed at USNO saw "first light". This 40 inch aperture instrument was also the second (and final) telescope made by famed optician,
George Willis Ritchey. The
Ritchey–Chrétien telescope design has since become the
de facto optical design for nearly all major telescopes, including the famed
Keck telescopes and the space-borne
Hubble Space Telescope. Because of
light pollution in the
Washington metropolitan area, USNO relocated the 40 inch telescope to
Flagstaff, Arizona. A new Navy command, now called the
USNO Flagstaff Station (NOFS), was established there. Those operations began in 1955. Within a decade, the Navy's largest telescope, the 61 inch "
Kaj Strand Astrometric Reflector" was built; it saw light at Flagstaff in 1964. USNO continues to maintain its
dark-sky observatory,
NOFS, near
Flagstaff. This facility now oversees the
Navy Precision Optical Interferometer.
History of the time service By the early 1870s the USNO daily noon-time signal was distributed electrically, nationwide, via the
Western Union Telegraph Company. Time was also "sold" to the railroads and was used in conjunction with
railroad chronometers to schedule American rail transport. Early in the 20th century, the service was broadcast by radio, with Arlington time signal available to those with
wireless receivers. In November 1913 the
Paris Observatory, using the
Eiffel Tower as an antenna, exchanged sustained wireless (radio) signals with the U.S. Naval Observatory to determine the exact difference of longitude between the two institutions, via an antenna in
Arlington, Virginia. The U.S. Naval Observatory in Washington continues to be a major authority in the areas of
Precise Time and Time Interval,
Earth orientation,
astrometry, and celestial observation. In collaboration with many national and international scientific establishments, it determines the timing and astronomical data required for accurate
navigation,
astrometry, and fundamental
astronomy, and
calculation methods — and distributes this information (such as
star catalogs) on-line and in the annual publications
The Astronomical Almanac and
The Nautical Almanac. Former USNO director
Gernot M. R. Winkler initiated the "
Master clock" service that the USNO still operates, and which provides
precise time to the
GPS satellite constellation run by the
United States Space Force. The alternate Master Clock time service continues to operate at
Schriever Space Force Base in
Colorado. ==Departments==