| Naval Support Facility US Naval Observatory | |
|---|---|
| Part of Naval Support Activity Washington | |
| Northwest Washington, D.C. in the United States | |
 An aerial view of the United States Naval Observatory in 2004 | |
 | |
| Site information | |
| Type | Military observatory andofficial residence of the US Vice President |
| Owner | Department of Defense |
| Operator | US Navy |
| Controlled by | Naval District Washington |
| Condition | Operational |
| Website | www |
| Official name | Naval Observatory Historic District (New Naval Observatory)[1] |
| Location | |
  NSF US Naval Observatory  NSF US Naval Observatory | |
| Coordinates | 38°55′17″N77°4′1″W / 38.92139°N 77.06694°W /38.92139; -77.06694 |
| Site history | |
| Built | 1830 (1830) (as Depot of Charts and Instruments) |
| In use | 1830–present |
| Garrison information | |
| Current commander | Captain Mark Burns |
| Garrison | United States Naval Observatory |
TheUnited States Naval Observatory (USNO) is ascientific and military facility that producesgeopositioning,navigation andtimekeeping data for theUnited States Navy and theUnited States Department of Defense.[2] Established in 1830 as theDepot of Charts and Instruments, it is one of the oldestscientific agencies in theUnited States,[3] and remains the country's leading facility for astronomical and timing data.[4]
The observatory is located inNorthwestWashington, D.C. at the northwestern end ofEmbassy Row. It is among the few pre-20th centuryastronomical observatories located in an urban area. In 1893, in an effort to escapelight pollution, it was relocated fromFoggy Bottom near the city's center, to its Northwest Washington, D.C. location.
The USNO has conducted significant scientific studies throughout its history, including measuring the speed of light, observing solar eclipses, and discovering the moons of Mars.[5] Its achievements include providing data for the first radio time signals, constructing some of the earliest and most accurate telescopes of their kind, and helping developuniversal time.[4] The Naval Observatory performs radioVLBI-based positions ofquasars forastrometry andgeodesy with numerous global collaborators (IERS), in order to produceEarth orientation parameters and to realize thecelestial reference system (ICRF).
Aside from its scientific mission, since the 1970s the Naval Observatory campus hoststhe official residence of thevice president of the United States.
PresidentJohn 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.[6]
The names "National Observatory" and "Naval Observatory" were both used for 10 years, until the Secretary of the Navy officially adopted the latter.[7]
Adams had made protracted efforts to bring astronomy to a national level.[8][9] He spent many nights at the observatory, watching and charting the stars, which had always been one of his interests.
Established by order of theUnited States Secretary of the NavyJohn Branch on 6 December 1830 as the Depot of Charts and Instruments,[10] the Observatory rose from humble beginnings: Placed under the command of LieutenantLouis M. Goldsborough, with an annual budget of $330; its primary function was the restoration, repair, and rating of navigational instruments.
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."[11] Lt. Gilliss visited the principal observatories of Europe with the mission to purchase telescopes and other scientific devices, and books.[12]
The observatory's primary mission was to care for theUnited States Navy'smarine chronometers, charts, and other navigational equipment. Itcalibrated ships' chronometers by timing thetransit ofstars across themeridian. It opened in 1844 inFoggy Bottom, north of the site of theLincoln Memorial and west of theWhite House.
In 1893, the observatory moved to its current location in Northwest Washington, D.C.[13] located on a 2000 foot circle of land atop "Observatory Hill", overlookingMassachusetts Avenue.
In 2017, the facilities were listed on theNational Register of Historic Places.[14]
The first superintendent was Navy CommanderM.F. Maury. Maury had the world's firstvulcanizedtime ball, created to his specifications byCharles 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 ofmean 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 viatelegraph 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.[15]
In 1849, the Nautical Almanac Office (NAO) was established inCambridge, Massachusetts as a separate organization. In 1866, it was moved toWashington, D.C., operating near Fort Myer. It relocated to the U.S. Naval Observatory grounds in 1893.[16]
On 20 September 1894, the NAO became a "branch" of USNO; however, it remained autonomous for several years.[16]
The site houses the largest astronomy library in the United States (and the largest astrophysical periodicals collection in the world).[17] The library includes a large collection of rare physics and astronomy books from the past millennium.
An early scientific duty assigned to the Observatory was the U.S. contribution to the definition of theAstronomical Unit, or theAU, which defines a standardmean 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 thetransit of Venus by a number of countries since 1639 resulted in a progressively more accurate definition of theAU.
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 thesolar parallax, after adjustments, of 8.809″, with a probable error of 0.0059″, yielding a U.S.-determined Earth-Sun distance of 92,797,000 mi (149,342,000 km), with a probable error of 59,700 mi (96,100 km). The calculated distance was a significant improvement over several previous estimates.[18]
The telescope used for the discovery of theMoons of Mars was the 26 inch (66 cm)refractor telescope, then located atFoggy Bottom, Washington, DC.[19] In 1893 it was moved to its Northwest DC location.[20]
In 1934, the largest optical telescope installed at USNO saw "first light". This 40 inch aperture instrument[21] was also the second (and final) telescope made by famed optician,George Willis Ritchey. TheRitchey–Chrétien telescope design has since become thede facto optical design for nearly all major telescopes, including the famedKeck telescopes and the space-borneHubble Space Telescope.
Because oflight pollution in theWashington metropolitan area, USNO relocated the 40 inch telescope toFlagstaff, Arizona. A new Navy command, now called theUSNO Flagstaff Station (NOFS), was established there. Those operations began in 1955.[22] Within a decade, the Navy's largest telescope, the 61 inch "Kaj Strand Astrometric Reflector" was built; it saw light at Flagstaff in 1964.[23]
USNO continues to maintain itsdark-sky observatory,NOFS, nearFlagstaff. This facility now oversees theNavy Precision Optical Interferometer.[24]
By the early 1870s the USNO daily noon-time signal was distributed electrically, nationwide, via theWestern Union Telegraph Company. Time was also "sold" to the railroads[25] and was used in conjunction withrailroad chronometers to schedule American rail transport. Early in the 20th century, the service was broadcast by radio, with Arlington time signal available to those withwireless receivers.
In November 1913 theParis Observatory, using theEiffel Toweras 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 inArlington, Virginia.[26]
The U.S. Naval Observatory in Washington continues to be a major authority in the areas ofPrecise 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 accuratenavigation,astrometry, and fundamentalastronomy, andcalculation methods — and distributes this information (such asstar catalogs)[27] on-line and in the annual publicationsThe Astronomical Almanac andThe Nautical Almanac.[28]
Former USNO directorGernot M. R. Winkler initiated the "Master clock" service that the USNO still operates,[29][30] and which providesprecise time to theGPS satellite constellation run by theUnited States Space Force. The alternate Master Clock time service continues to operate atSchriever Space Force Base inColorado.
In 1990 two departments were established:Orbital Mechanics and Astronomical Applications, with theNautical Almanac Office a division in Astronomical Applications.[16][31] TheOrbital Mechanics Department operated underP. Kenneth Seidelmann until 1994, when the department was abolished and its functions transferred to a group within the Astronomical Applications Department.[16]
In 2010, USNO's astronomical 'department' known as theNaval Observatory Flagstaff Station (NOFS) was officially made autonomous as an Echelon 5 command, separate from, but still reporting to the USNO in Washington. In the alpine woodlands above 7,000 feet altitude outsideFlagstaff, Arizona,NOFS performs its national, Celestial Reference Frame (CRF) mission under dark skies in that region.
A house situated on the grounds of the observatory, at Number One Observatory Circle, has been the official residence of thevice president of the United States since 1974. It is protected by tight security control enforced by theSecret Service. The house is separated from the Naval Observatory.
Before serving as the vice president's residence, it was that of the observatory's superintendent, and later thechief of naval operations.[32]
The U.S. Naval Observatory operates two "Master Clock" facilities, one in Washington, DC, and the other atSchriever SFB nearColorado Springs, CO.
The observatory also operates four[34]rubidiumatomic fountain clocks, which have a stability reaching 7×10−16.[35] The observatory plans to build several more of this type for use at its two facilities.[33]
The clocks used for the USNO timescale are kept in 19 environmental chambers, whose temperatures are kept constant to within 0.1°C. The relative humidities are kept constant in all maser, and most cesiums enclosures, to within 1%. Time-scale management only uses the clocks in Washington, DC, and of those, preferentially uses the clocks that currently conform reliably to the time reports of the majority. It is the combined 'vote' of the ensemble that constitutes the otherwise-fictitious "Master Clock". The time-scale computations on 7 June 2007 weighted 70 of the clocks into the standard.[33]
The U.S. Naval Observatory provides public time service via 26 NTP[33] servers on the publicInternet,[36] and via telephone voice announcements:[37]
The voice of actor Fred Covington (1928–1993)[38] has been announcing the USNO time since 1978.[39]
The voice announcements always begin with the local time (daylight or standard), and include a background of 1 second ticks. Local time announcements are made on the minute, and 15, 30, and 45 seconds after the minute.Coordinated Universal Time (UTC) is announced 5 seconds after the local time.[40] Upon connecting, only the second-marking ticks are heard for the few seconds before the next scheduled local time announcement
The USNO also operates a modem time service,[41] and provides time to the Global Positioning System.
The United States Naval Observatory Instrument shop has been designing and manufacturing precise instrumentation since the early 1900s.[42]
Astronomy and observatories
Technology and technical resources
USNO personnel
These different names for the observatory, and the term 'Hydrographic Office', were used interchangeably until December 1854, when the Secretary of the Navy officially ruled that the proper designation was "The United States Naval Observatory and Hydrographical office".
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