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{{Redirect|USNO}}
{{short description|Scientific agency in the United States}}
{{hatnote group|
[[File:U.S. Naval Observatory-seal.gif|thumb|right|upright=1.3|The Seal of the USNO with a quote from the [[Astronomica (Manilius)|Astronomica]] by [[Marcus Manilius]], ''Adde gubernandi studium: Pervenit in astra, et pontum caelo conjunxit'' [''Increase the study of navigation: It arrives in the stars, and marries the sea with heaven''.] ]]
{{Redirect|USNO}}
{{Distinguish|United States Naval Observatory Flagstaff Station}}
}}
{{Infobox military installation
| name = Naval Support Facility US Naval Observatory
| ensign =
| ensign_size =
| native_name =
| partof = Naval Support Activity Washington
| location = [[Northwest (Washington, D.C.)|Northwest Washington, D.C.]]
| nearest_town = <!-- used in military test site infobox -->
| country = the United States
| image = United States Naval Observatory.aerial view.jpg
| alt =
| caption = An aerial view of the United States Naval Observatory in 2004
| image2 = [[File:United states navy observatory seal.jpg|150px]]
| alt2 =
| caption2 =
| type = [[Observatory|Military observatory]] and [[Number One Observatory Circle|official residence of the US Vice President]]
| coordinates = {{Wikidatacoord|Q11700|region:US-DC_type:landmark|display=inline,title}}
| gridref =
| image_map =
| image_mapsize =
| image_map_alt =
| image_map_caption =
| pushpin_map = United States Washington, D.C.#USA
| pushpin_mapsize =
| pushpin_map_alt =
| pushpin_map_caption =
| pushpin_relief =
| pushpin_image =
| pushpin_label = NSF US Naval Observatory
| pushpin_label_position =
| pushpin_mark =
| pushpin_marksize =
| ownership = [[United States Department of Defense|Department of Defense]]
| operator = [[United States Navy|US Navy]]
| controlledby = [[Naval District Washington]]
| open_to_public = <!-- for out of use sites/sites with museums etc -->
| site_other_label = <!-- for renaming "Other facilities" in infobox -->
| site_other = <!-- for other sorts of facilities – radar types etc -->
| site_area = <!-- area of site m2, km2 square mile etc -->
| code = <!--facility/installation code -->
| built = {{Start date|1830}} (as Depot of Charts and Instruments)
| used = 1830–present<!-- {{End date|1946}} -->
| builder =
| materials =
| fate = <!--changed from demolished parameter-->
| condition = Operational
| battles =
| events =
| current_commander = [[Captain (United States O-6)|Captain]] Mark Burns
| past_commanders = <!-- past notable commander(s) -->
| garrison = United States Naval Observatory
| occupants = <!-- squadrons only -->
| designations =
| website = {{Official URL}}
{{Infobox designation list
|embed = yes
|designation1 = District of Columbia Inventory of Historic Sites
|designation1_offname = Naval Observatory Historic District (New Naval Observatory)<ref>{{Cite web |date=30 September 2009 |title=District of Columbia Inventory of Historic Sites |url=https://planning.dc.gov/sites/default/files/dc/sites/op/publication/attachments/Inventory%202009%200%20Alpha%20Version%2003%2011.pdf |access-date=25 May 2023 |website=DC.GOV – Office of Planning |publisher=State Historic Preservation Office, D.C. Office of Planning |page=107 |archive-date=1 October 2020 |archive-url=https://web.archive.org/web/20201001205634/https://planning.dc.gov/sites/default/files/dc/sites/op/publication/attachments/Inventory%202009%200%20Alpha%20Version%2003%2011.pdf |url-status=live }}</ref>
|designation1_date =
}}
}}
[[File:U.S. Naval Observatory-seal.gif|thumb|right|upright=1.3|The Seal of the USNO with a quote from the [[Astronomica (Manilius)|Astronomica]] by [[Marcus Manilius]], ''Adde gubernandi studium: Pervenit in astra, et pontum caelo conjunxit'' [''Increase the study of navigation: It arrives in the stars, and marries the sea with heaven''].]]
 
The '''United States Naval Observatory''' ('''USNO''') is a [[Observatory|scientific and military facility]] that produces [[geopositioning]], [[navigation]] and [[timekeeping]] data for the [[United States Navy]] and the [[United States Department of Defense]].<ref>{{cite web |title=National Executive Committee for Space-Based Positioning, Navigation, and Timing |website=pnt.gov |publisher=U.S. Government Printing Office |date=2011-06-17 |url=http://pnt.gov/101 |access-date=2011-07-27 |archive-date=2011-07-30 |archive-url=https://web.archive.org/web/20110730160143/http://www.pnt.gov/101/ |url-status=live }}</ref> Established in 1830 as the '''Depot of Charts and Instruments''', it is one of the oldest [[Science|scientific]] agencies in the [[United States]],<ref>{{cite web |title=The USNO's Mission |url=http://www.usno.navy.mil/USNO/about-us/the-usno-mission/ |access-date=2011-07-27 |website=usno.navy.mil |series=Naval Oceanography Portal |publisher=Naval Meteorology and Oceanography Command |archive-date=2009-12-24 |archive-url=https://web.archive.org/web/20091224145307/http://www.usno.navy.mil/USNO/about-us/the-usno-mission/ |url-status=dead }}</ref> and remains the country's leading authorityfacility for astronomical and timing data for all purposes.<ref name=":0">{{Cite web |title=USNO -— Our Command History — Naval Oceanography Portal |url=https://www.usno.navy.mil/USNO/about-us/a-brief-history/usno-command-history |access-date=2022-03-28 |website=usno.navy.mil |archive-date=2021-12-09 |archive-url=https://web.archive.org/web/20211209110903/https://www.usno.navy.mil/USNO/about-us/a-brief-history/usno-command-history |url-status=live }}</ref>
 
The observatory is located in [[Northwest, (Washington, D.C.)|Northwest]] [[Washington, D.C.]] at the northwestern end of [[Embassy Row]]. It is among the few pre-20th century [[Observatory|astronomical observatories]] located in an urban area;. initiallyIn located1893, in an effort to escape [[light pollution]], it was relocated from [[Foggy Bottom]] near the city's center, it was relocated to its currentNorthwest locationWashington, inD.C. 1893 to escape [[light pollution]]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.<ref>{{Cite web |title=A Brief History of the Naval Observatory — Naval Oceanography Portal |url=https://www.usno.navy.mil/USNO/about-us/a-brief-history |access-date=2022-03-28 |website=www.usno.navy.mil |archive-date=2022-03-28 |archive-url=https://web.archive.org/web/20220328091707/https://www.usno.navy.mil/USNO/about-us/a-brief-history |url-status=live }}</ref> Its achievements includinginclude providing data for the first radio time signals, constructing some of the earliest and most accurate telescopes of their kind, and helping develop [[Coordinated Universal Time|universal time]].<ref name=":0" /> The Naval Observatory performs radio [[Very-long-baseline interferometry|VLBI]]-based positions of [[quasar]]s for [[astrometry]] and [[geodesy]] with numerous global collaborators ([[International Earth Rotation and Reference Systems Service|IERS]]), in order to produce [[Earth orientation parameters]] and to realize the [[celestial reference system]] ([[International Celestial Reference Frame|ICRF]]).
 
Aside from its scientific mission, since the 1970s the Naval Observatory campus hosts [[Number One Observatory Circle|the official residence]] of the [[Vice President of the United States|vice president of the United States]].
 
== History ==
[[File:Usno-telescope-equalized-1.png|thumb|The 26&nbsp;inch (66&nbsp;cm) aperture telescope, with which [[Asaph Hall]] discovered the [[moons of Mars]] in 1877; the telescope is shown at its modern Northwest DC location.]]
[[Image:United States Naval Observatory.aerial view.jpg|thumb|right|Aerial view of the U.S. Naval Observatory Washington, DC, campus|400x400px]]
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.<ref>{{cite book |first=Steven J. |last=Dick |year=2003 |title=Sky and Ocean Joined: The U.S. Naval Observatory 1830-2000 |publisher=Cambridge University Press |isbn=9780521815994 |url=https://books.google.com/books?id=DNwfG5hQ7-YC&pg=PA54 |access-date=2013-08-04 |via=Google Books}}</ref>
[[File:Usno-telescope-equalized-1.png|thumb|The 26&nbsp;inch (66&nbsp;cm) aperture telescope, with which [[Asaph Hall]] discovered the [[moons of Mars]] in 1877; the telescope is shown here at its new location.]]
=== Early presidential astronomical interest ===
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.<ref>{{cite book |first=Steven J. |last=Dick |year=2003 |title=Sky and Ocean Joined: The U.S. Naval Observatory 1830-2000 |isbn=9780521815994 |url=https://books.google.com/books?id=DNwfG5hQ7-YC&pg=PA54 |access-date=2013-08-04 |via=Google Books}}</ref>
 
The names "National Observatory" and "Naval Observatory" were both used for 10&nbsp;years, until the Secretary of the Navy officially adopted the latter.<ref>{{cite book | first = Frances Leigh | last = Williams | date = 1963 | chapter = VIII.&nbsp;Scientific opportunity at last | title = Matthew Fontaine Maury: Scientist of the Sea | page = 164 | place = New Brunswick, NJ | publisher = Rutgers University Press | quote = These different names for the observatory, and the term ‘Hydrographic Office’, were used interchangeably until December&nbsp;1854, when the Secretary of the Navy officially ruled that the proper designation was “The United States Naval Observatory and Hydrographical office”.}}</ref>
 
Adams had made protracted efforts to bring astronomy to a national level at that time.<ref>{{cite journal |last1=Dick |first1=S.J. |year=1991 |title=The origins of the Dominion Observatory, Ottawa |journal=Journal for the History of Astronomy |volume=22 |pages=45–53 |doi=10.1177/002182869102200106 |s2cid=117369344 |bibcode=1991JHA....22...31D}}</ref><ref>{{cite journal | last = Portolano | first = M. |date=2013-03-25 |title=John Quincy Adams' rhetorical crusade for astronomy |journal=Isis |volume=91 |issue=3 |pages=480–503 | doi=10.1086/384852 |s2cid=25585014 |pmid=11143785 |url=https://zenodo.org/record/1235690 |access-date=2018-05-18 |archive-date=2020-09-27 |archive-url=https://web.archive.org/web/20200927075152/https://zenodo.org/record/1235690 |url-status=live }}</ref> He spent many nights at the observatory, watching and charting the stars, which had always been one of Adams'his interests.
 
Established by order of the [[United States Secretary of the Navy]] [[John Branch]] on 6&nbsp;December 1830 as the Depot of Charts and Instruments,<ref>{{Cite book |last1=Matchette |first1=R.B. |display-authors=etal |date=1995 |title=Guide to Federal Records in the National Archives of the United States. |publisher=National Archives and Records Administration |location=Washington, DC |url=https://www.archives.gov/research/guide-fed-records/groups/078.html |access-date=2017-09-17 |archive-date=2017-12-03 |archive-url=https://web.archive.org/web/20171203224204/https://www.archives.gov/research/guide-fed-records/groups/078.html |url-status=live }}</ref> 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.
=== Establishment as an optical equipment depot ===
Established by order of the [[United States Secretary of the Navy]] [[John Branch]] on 6&nbsp;December 1830 as the Depot of Charts and Instruments,<ref>{{Cite book | last1 = Matchette | first1 = R.B. |display-authors=etal | date = 1995 | title = Guide to Federal Records in the National Archives of the United States. | publisher = National Archives and Records Administration | location = Washington, DC | url = https://www.archives.gov/research/guide-fed-records/groups/078.html
}}</ref> 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.
 
=== FederalOld observatoryNaval Observatory ===
{{Main|Old Naval Observatory}}
It was established as a national observatory in 1842 by federal law and a Congressional appropriation of $25,000. Lt.&nbsp;[[James Melville Gilliss|J.M. Gilliss]] was put in charge of "obtaining the instruments needed and books."<ref>{{cite web |url=https://www.usno.navy.mil/USNO/library/library-home/ |publisher=The James Melville Gilliss Library |title=Naval Oceanography Portal |website=www.usno.navy.mil}}</ref> Lt.&nbsp;Gilliss visited the principal observatories of Europe with the mission to purchase telescopes and other scientific devices, and books.<ref>{{cite news |title=The Naval Observatory |date=14 December 1842 |newspaper=[[The Baltimore Sun]] |page=1 |id={{ProQuest|533000734}} |via=ProQuest}}</ref>
It was established as a national observatory in 1842 by federal law and a Congressional appropriation of $25,000. Lt.&nbsp;[[James Melville Gilliss|J.M. Gilliss]] was put in charge of "obtaining the instruments needed and books."<ref>{{cite web |url=https://www.usno.navy.mil/USNO/library/library-home/ |publisher=The James Melville Gilliss Library |title=Naval Oceanography Portal |website=www.usno.navy.mil |access-date=2021-01-17 |archive-date=2021-01-24 |archive-url=https://web.archive.org/web/20210124152829/https://www.usno.navy.mil/USNO/library/library-home/ |url-status=live }}</ref> Lt.&nbsp;Gilliss visited the principal observatories of Europe with the mission to purchase telescopes and other scientific devices, and books.<ref>{{cite news |title=The Naval Observatory |date=14 December 1842 |newspaper=[[The Baltimore Sun]] |page=1 |id={{ProQuest|533000734}} |via=ProQuest}}</ref>
 
The observatory's primary mission was to care for the [[United States Navy]]'s [[marine chronometer]]s, charts, and other navigational equipment. It [[Calibration|calibrated]] ships' chronometers by timing the [[Transit (astronomy)|transit]] of [[star]]s across the [[meridian (astronomy)|meridian]]. It opened in 1844 in [[Foggy Bottom]], north of the present site of the [[Lincoln Memorial]] and west of the [[White House]] (see: [[Old Naval Observatory]]). The observatory moved to its present location in 1893<ref name="1894MNRAS">{{cite journal | title = The new U.S. Naval Observatory, Washington | journal = [[Monthly Notices of the Royal Astronomical Society]] | date = 1894 | volume = 54 | issue = 4 | page = 261 | bibcode = 1894MNRAS..54..261. | doi = 10.1093/mnras/54.4.240 | doi-access = free }}</ref> located on a 2000&nbsp;foot circle of land atop "Observatory Hill", overlooking [[Massachusetts Avenue (Washington, D.C.)|Massachusetts Avenue]].
 
In 1893, the observatory moved to its current location in Northwest Washington, D.C.<ref name="1894MNRAS">{{cite journal |title=The new U.S. Naval Observatory, Washington |journal=[[Monthly Notices of the Royal Astronomical Society]] |date=1894 |volume=54 |issue=4 |page=261 |bibcode=1894MNRAS..54..261. |doi=10.1093/mnras/54.4.240 |doi-access=free}}</ref> located on a 2000&nbsp;foot circle of land atop "Observatory Hill", overlooking [[Massachusetts Avenue (Washington, D.C.)|Massachusetts Avenue]].
The facilities were listed on the [[National Register of Historic Places]] in 2017.<ref>{{cite web |url=https://www.nps.gov/nr/listings/20170119.htm |title=Weekly list of actions, 12/20/2016 through 1/13/2017 |publisher=National Park Service |access-date=2017-01-26}}</ref>
 
In 2017, the facilities were listed on the [[National Register of Historic Places]].<ref>{{cite web |url=https://www.nps.gov/nr/listings/20170119.htm |title=Weekly list of actions, 12/20/2016 through 1/13/2017 |publisher=National Park Service |access-date=2017-01-26 |archive-date=2017-01-25 |archive-url=https://web.archive.org/web/20170125190225/https://www.nps.gov/nr/listings/20170119.htm |url-status=live }}</ref>
=== The iconic time-ball ===
 
===The time ball===
The first superintendent was Navy Commander [[Matthew Fontaine Maury|M.F. Maury]]. Maury had the world's first [[Vulcanization|vulcanized]] [[time ball]], created to his specifications by [[Charles Goodyear]] for the U.S.&nbsp;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[[noon|mean Solarsolar Noonnoon]]; 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 [[Telegraphy|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.<ref>{{cite APOD |title=The USNO millennium time ball |date=1999-10-29 |access-date=2015-12-27}}</ref>
=== The Nautical Almanac Office ===
In 1849 the Nautical Almanac Office (NAO) was established in [[Cambridge, Massachusetts]] as a separate organization. It was moved to [[Washington, D.C.]] in 1866, originally operating near Fort Myer. It relocated to the U.S. Naval Observatory grounds in 1893.<ref name="sky_and_ocean"/>
 
===Nautical Almanac Office===
On 20&nbsp;September 1894, the NAO became a "branch" of USNO; however, it remained autonomous for several years afterward.<ref name="sky_and_ocean"/>
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.<ref name="sky_and_ocean"/>
 
On 20&nbsp;September 1894, the NAO became a "branch" of USNO; however, it remained autonomous for several years.<ref name="sky_and_ocean"/>
=== Measuring the astonomical unit ===
 
The site houses the largest astronomy library in the United States (and the largest astrophysical periodicals collection in the world).<ref>{{cite web |publisher=Naval Meteorology and Oceanography Command |title=The James Melville Gilliss Library |series=Naval Oceanography Portal |website=usno.navy.mil |url=http://www.usno.navy.mil/USNO/library |access-date=2011-07-27 |archive-date=2011-07-26 |archive-url=https://web.archive.org/web/20110726020826/http://www.usno.navy.mil/USNO/library |url-status=dead }}</ref> 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|Astronomical Unit]], or the {{sc|AU}}, which defines a standard [[arithmetic mean|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 {{sc|AU}}.
 
Relying strongly on photographic methods, the naval observers returned 350&nbsp;[[photographic plate]]s in 1874, and 1,380&nbsp;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 [[parallax|solar parallax]], after adjustments, of 8.809″, with a probable error of 0.0059″, yielding a U.S.-determined Earth-Sun distance of {{convertcvt|92,797,000|mi|km}}, with a probable error of {{convertcvt|59,700|mi|km}}. The calculated distance was a significant improvement over several previous estimates.<!-- Note that theThe preceding paragraph contains verbatim text producedwritten by a U.S. Government employee during the course of his duties, which makes it copyright-free and thus in the public domain. --><ref name="NASA-Dick">{{cite journal |last=Dick |first=Steven J. |orig-year=2004 |title=The American Transit of Venus Expeditions of 1874 and 1882 |journal=[[Proceedings of the International Astronomical Union]] |pages=100–110 |doi=10.1017/S1743921305001304 |date=23 May 2005 <!-- Published online 23 May 2005 --> |volume=2004 |bibcode=2005tvnv.conf..100D |type=abstract |doi-access=free }}</ref>
 
=== The new 26&nbsp;inch and 40&nbsp;inch refractors ===
The telescope used for the discovery of the [[Moons of Mars]] was the 26&nbsp;inch (66&nbsp;cm) [[refractor]] (a telescope containing only lenses), then located at [[Foggy Bottom]], Washington, DC.<ref>{{cite web |title=Telescope: Naval Observatory 26&nbsp;inch refractor |publisher=[[Space Telescope Science Institute]] |place=Baltimore, MD |url=http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/scopes/naval/index.php |access-date=2013-10-18 |archive-date=2013-10-18 |archive-url=https://archive.today/20131018184452/http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/scopes/naval/index.php |url-status=live }}</ref> In 1893 it was moved to theits presentNorthwest DC location.<ref>{{cite web |title=The 26-inch "Great Equatorial" Refractor |website=usno.navy.mil |publisher=[[United States Navy]] |department=U.S. Naval Observatory |url=http://www.usno.navy.mil/USNO/about-us/the-26-inch-refractor |access-date=2013-10-18 |archive-date=2012-10-08 |archive-url=https://web.archive.org/web/20121008034337/http://www.usno.navy.mil/USNO/about-us/the-26-inch-refractor/ |url-status=dead }}</ref>
 
[[Image:NOFS panorama sm.jpg|thumb|right|upright=1.3|alt=NOFS.|Naval Observatory Flagstaff Station]]
In 1934, the lastlargest (then) largeoptical telescope to be installed at USNO saw "first light". This 40&nbsp;inch aperture instrument<ref>{{cite web |series=U.S. Naval Observatory Flagstaff |title=1.0&nbsp;m Ritchey-Chretien Reflector |date=1998-01-25 |website=nofs.navy.mil |url=http://www.nofs.navy.mil/about_NOFS/telescopes/rc.html |access-date=2011-07-27 |archive-date=2011-07-28 |archive-url=https://web.archive.org/web/20110728050840/http://www.nofs.navy.mil/about_NOFS/telescopes/rc.html |url-status=dead }}</ref> was also the second (and final) telescope made by famed optician, [[George Willis Ritchey]]. The [[Ritchey–Chrétien telescope]] design has since become the ''de&nbsp;facto'' optical design for nearly all major telescopes, including the famed [[W. M. Keck Observatory|Keck telescopes]] and the space-borne [[Hubble Space Telescope]].
 
Because of [[light pollution]] in the [[Washington metropolitan area]], USNO relocated the 40&nbsp;inch telescope to [[Flagstaff, Arizona]]. A new Navy command, now called the [[United States Naval Observatory Flagstaff Station|USNO Flagstaff Station]] (NOFS), was established there. Those operations began in 1955.<ref>{{cite web |series=USNO Flagstaff Station |title=History |website=nofs.navy.mil |url=http://www.nofs.navy.mil/about_NOFS/hist.html |access-date=2011-07-27 |archive-date=2011-07-28 |archive-url=https://web.archive.org/web/20110728050902/http://www.nofs.navy.mil/about_NOFS/hist.html |url-status=dead }}</ref> Within a decade, the Navy's largest telescope, the 61&nbsp;inch "[[Kaj Aage Gunnar Strand|Kaj Strand]] Astrometric Reflector" was built; it saw light at Flagstaff in 1964.<ref>{{cite web |series=U.S. Naval Observatory Flagstaff |title=1.55&nbsp;m Astrometric Reflector |date=2001-05-24 |website=nofs.navy.mil |url=http://www.nofs.navy.mil/about_NOFS/telescopes/ksar.html |access-date=2011-07-27 |archive-date=2011-07-26 |archive-url=https://web.archive.org/web/20110726143905/http://www.nofs.navy.mil/about_NOFS/telescopes/ksar.html |url-status=dead }}</ref>
 
USNO continues to maintain its [[Dark-sky movement|dark-sky]] observatory, [[United States Naval Observatory Flagstaff Station|NOFS]], near [[Flagstaff, Arizona|Flagstaff]]. This facility now oversees the [[Navy Precision Optical Interferometer]].<ref>{{cite web |title=Navy Precision Optical Interferometer (NPOI) |website=[[Lowell Observatory]] |url=http://www.lowell.edu/npoi/ |access-date=2009-10-08 |archive-date=2009-12-15 |archive-url=https://web.archive.org/web/20091215061606/http://www.lowell.edu/npoi/ |url-status=live }}</ref> The alternate Master Clock, [[#Time_service|discussed below]], continues to operate at [[Schriever Air Force Base]] in [[Colorado]].
 
=== 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”"sold" to the railroads<ref>{{citationcite book needed|reason last=needBartky citation| offirst=Ian whatR. is| currentlytitle=Selling athe publicTrue resourceTime being| “privatized”publisher=Stanford forUniversity salePress at| thispublication-place=Stanford, Calif date| date=July2000 2019}}| toisbn=978-0-8047-3874-3 the| railroadsp=199}}</ref> and was used in conjunction with [[railroad chronometer]]s to schedule American rail transport. Early in the 20th&nbsp;century, the service was broadcast by radio, with Arlington time signal available to those with [[wireless]] receivers.
 
In November&nbsp;1913 the [[Paris Observatory]], using the [[Eiffel Tower]] [[Eiffel Tower#Communications|as an antenna]], exchanged sustained wireless (radio) signals with the U.S.&nbsp;Naval Observatory to determine the exact difference of longitude between the two institutions, via an antenna in [[Arlington County, Virginia|Arlington, Virginia]].<ref>{{cite news |title=Paris time by wireless |date=22 November 1913 |newspaper=[[The New York Times]] |page=1}}</ref>
 
The U.S. Naval Observatory in Washington no longer obtains significant astrometric observations, but it continues to be a major authority in the areas of [[Precise Time and Time Interval]], [[Earth Orientation Parameters|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 [[Naval Observatory Vector Astrometry Subroutines|calculation methods]] — and distributes this information (such as [[Star catalogue|star catalogs]])<ref>{{cite web |publisher=Naval Meteorology and Oceanography Command |title=Catalog information |series=Naval Oceanography Portal |website=usno.navy.mil |url=http://www.usno.navy.mil/USNO/astrometry/information/catalog-info |access-date=2011-07-27 |archive-date=2011-07-26 |archive-url=https://web.archive.org/web/20110726022418/http://www.usno.navy.mil/USNO/astrometry/information/catalog-info |url-status=dead }}</ref> on-line and in the annual publications ''[[The Astronomical Almanac]]'' and ''[[The Nautical Almanac]]''.<ref>{{cite web |publisher=Naval Meteorology and Oceanography Command |title=Interactive catalog and image search |series=Naval Oceanography Portal |website=usno.navy.mil |url=http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/icas/fchpix |access-date=2011-07-27 |archive-date=2011-07-26 |archive-url=https://web.archive.org/web/20110726022359/http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/icas/fchpix |url-status=live }}</ref>
 
The general public knows about the “Master Clock”, the observatory’s highly accurate ensemble of [[atomic clock]]s, and its one-off time-ball re-enactment for the year-2000 celebration.<ref>{{cite APOD |title=The USNO millennium time ball |date=1999-10-29 |access-date=2015-12-27}}</ref> The site houses the largest astronomy library in the United States (and the largest astrophysical periodicals collection in the world).<ref>{{cite web |publisher=Naval Meteorology and Oceanography Command |title=The James Melville Gilliss Library |series=Naval Oceanography Portal |website=usno.navy.mil |url=http://www.usno.navy.mil/USNO/library |access-date=2011-07-27}}</ref> The library includes a large collection of rare, often famous, physics and astronomy books from the past millennium.
 
Former USNO director [[Gernot M. R. Winkler]] initiated the "[[Master clock|"Master Clock"]]" service that the USNO still operates,<ref>{{cite web |title=USNO Master Clock |url=http://www.usno.navy.mil/USNO/time/master-clock/ |access-date=2011-07-27 |website=usno.navy.mil |series=Naval Oceanography Portal |archive-date=2010-12-07 |archive-url=https://web.archive.org/web/20101207082711/http://www.usno.navy.mil/USNO/time/master-clock |url-status=dead }}</ref><ref>{{cite web |url=http://www.usno.navy.mil/USNO/time/master-clock/ |archive-url=https://web.archive.org/web/20220120185645/http://www.usno.navy.mil/USNO/time/master-clock/ |archive-date=2022-01-20 |title=USNO Master Clock — Naval Oceanography Portal}}</ref> and which provides [[Atomic clock|precise time]] to the [[GPS satellite blocks|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==
In 1990 two departments were established: [[Celestial mechanics|Orbital Mechanics]] and Astronomical Applications, with the [[Nautical Almanac]] Office a division in Astronomical Applications.<ref name="sky_and_ocean"/><ref>{{cite journal |last=Seidelmann |first=P.K. |year=1997 |title=Nautical Almanac Office 1975–1996 |journal=American Astronomical Society Meeting Abstracts |volume=191 |pages=01.05 |bibcode=1997AAS...191.0105S |url=http://aas.org/archives/BAAS/v29n5/aas191/abs/S001005.html |access-date=2011-07-27 |archive-date=2013-03-09 |archive-url=https://web.archive.org/web/20130309020850/http://aas.org/archives/BAAS/v29n5/aas191/abs/S001005.html |url-status=live }}</ref> The [[Celestial mechanics|Orbital Mechanics]] Department operated under [[P. Kenneth Seidelmann]] until 1994, when the department was abolished and its functions transferred to a group within the Astronomical Applications Department.<ref name="sky_and_ocean">{{cite book | title = Sky and Ocean Joined: The U.S. Naval Observatory, 1830–2000 | first = Steven J. | last = Dick | publisher = Cambridge University Press | date = 2003 | isbn = 978-0-521-81599-4 | pages= 547–548, 574 }}</ref>
 
In 2010, USNO's astronomical 'department' known as the [[United States Naval Observatory Flagstaff Station|Naval Observatory Flagstaff Station (NOFS)]] was officially made autonomous as an Echelon&nbsp;5 command, separate from, but still reporting to the USNO in Washington. In the alpine woodlands above 7,000&nbsp;feet altitude outside [[Flagstaff, Arizona]], [[United States Naval Observatory Flagstaff Station|NOFS]] performs its national, Celestial Reference Frame (CRF) mission under dark skies in that region.
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[[Image:1OC2003.jpg|thumb|right|[[Number One Observatory Circle]], official home of the [[Vice President of the United States|U.S. vice president]].]]
{{Main|Number One Observatory Circle}}
A house situated on the grounds of the observatory, at Number One Observatory Circle, has been the official residence of the [[Vice President of the United States|vice president of the United States]] since 1974. It is protected by tight security control enforced by the [[United States Secret Service|Secret Service]]. The house is separated from the Naval Observatory.
 
ItBefore formerly servedserving as the vice president's residence, it was that of the observatory's superintendent, and later was the residence of the [[Chief of Naval Operations|chief of naval operations]], and finally the [[Vice President of the United States|vice president]].<ref>{{cite web |title=The Vice-President's residence and office |publisher=U.S. [[National Archives]] |website=archives.gov |url=https://obamawhitehouse.archives.gov/about/vp-residence |access-date=2013-02-27 |archive-date=2023-10-28 |archive-url=https://web.archive.org/web/20231028015859/https://obamawhitehouse.archives.gov/1600/vp-residence |url-status=live }}</ref>
 
==Time service==
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The U.S. Naval Observatory operates two “Master Clock” facilities, one in Washington, DC, and the other at [[Schriever Space Force Base|Schriever SFB]] near [[Colorado Springs, Colorado|Colorado Springs, CO]].
* The primary facility, in Washington, D.C. maintains 57&nbsp;[[Hewlett-Packard|HP]]/[[Agilent Technologies|Agilent]]/[[Symmetricom]] 5071A-001 high performance [[cesium]] atomic clocks and 24&nbsp;[[hydrogen maser]]s.<ref name="matsakis2010"/>
* The alternate facility, at [[Schriever Space Force Base|Schriever Space Force Base]], maintains 12&nbsp;cesium clocks and 3&nbsp;masers.<ref name="matsakis2010">{{cite report |first=Demetrios |last=Matsakis |date=2010-09-20 |title=Report from the U.S. Naval Observatory |collaboration=Civil GPS Service Interface Committee |publisher=[[United States Coast Guard]] |url=http://www.navcen.uscg.gov/pdf/cgsicMeetings/50/%5B15%5DUSNOreport_matsakis_sep2010.pdf |archive-url=https://web.archive.org/web/20110614023137/http://www.navcen.uscg.gov/pdf/cgsicMeetings/50/%5B15%5DUSNOreport_matsakis_sep2010.pdf |archive-date=2011-06-14 |url-status=live |access-date=2010-10-31}}</ref>
 
The observatory also operates four<ref>{{cite press release |url=http://www.usno.navy.mil/USNO/tours-events/u.s.-naval-observatory-declares-full-operational-capability-for-rubidium-fountain-clocks |title=U.S. Naval Observatory declares full operational capability for rubidium fountain clocks |date= |access-date=2014-04-10 |archive-date=2015-09-22 |archive-url=https://web.archive.org/web/20150922043917/http://www.usno.navy.mil/USNO/tours-events/u.s.-naval-observatory-declares-full-operational-capability-for-rubidium-fountain-clocks |url-status=live }}</ref> [[rubidium]] [[atomic fountain]] clocks, which have a stability reaching 7{{e|-16}}.<ref>{{cite report |title=Initial Evaluation of the USNO Rubidium Fountain |date=2006-01-27 |publisher=[[United States Navy]] |department=U.S. Naval Observatory |url=http://ad.usno.navy.mil/edboard/060127.pdf |access-date=2010-11-17 |url-status=dead |archive-url=https://web.archive.org/web/20110615095955/http://ad.usno.navy.mil/edboard/060127.pdf |archive-date=2011-06-15}}</ref> The observatory plans to build several more of this type for use at its two facilities.<ref name="matsakis2010"/>
 
The clocks used for the USNO timescale are kept in 19&nbsp;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&nbsp;June 2007 weighted 70 of the clocks into the standard.<ref name="matsakis2010"/>
 
[[File:US Naval Observatory Master Clock.jpg|thumb|US Naval Observatory outside display of the [[master clock]] time]]
The U.S. Naval Observatory provides public time service via 26&nbsp;[[Network Time Protocol|NTP]]<ref name="matsakis2010"/> servers on the public [[Internet]],<ref>{{cite web |title=USNO Network Time Servers |website=tycho.usno.navy.mil |url=http://tycho.usno.navy.mil/ntp.html |access-date=2011-07-27}}</ref> and via telephone voice announcements:<ref>{{cite web |title=Telephone Time |series=Naval Oceanography Portal |website=usno.navy.mil |url=http://www.usno.navy.mil/USNO/time/telephone-time |access-date=2011-07-27}}</ref>
The U.S. Naval Observatory provides public time service via 26&nbsp;[[Network Time Protocol|NTP]]<ref name="matsakis2010"/> servers on the public [[Internet]],<ref>{{cite web |title=USNO Network Time Servers |website=tycho.usno.navy.mil |url=http://tycho.usno.navy.mil/ntp.html |access-date=2011-07-27 |archive-date=2006-01-16 |archive-url=https://web.archive.org/web/20060116054653/http://tycho.usno.navy.mil/ntp.html |url-status=dead }}</ref> and via telephone voice announcements:<ref>{{cite web |title=Telephone Time |url=https://www.cnmoc.usff.navy.mil/Our-Commands/United-States-Naval-Observatory/Precise-Time-Department/Telephone-Time/ |access-date=2023-07-01 |archive-date=2023-07-01 |archive-url=https://web.archive.org/web/20230701173820/https://www.cnmoc.usff.navy.mil/Our-Commands/United-States-Naval-Observatory/Precise-Time-Department/Telephone-Time/ |url-status=live }}</ref>
* +1 202 762-1401 (Washington, DC)
* +1 202 762-1069 (Washington, DC)
* +1 719 567-6742 (Colorado Springs, CO)
The voice of actor [[Fred Covington (actor)|Fred Covington]] (1928–1993)<ref>{{cite magazine |title=The timekeeper behind America's master clock |date=5 December 2012 |magazine=[[Washingtonian (magazine)|Washingtonian]] |url=https://www.washingtonian.com/2012/12/05/the-timekeeper-behind-americas-master-clock/ |access-date=7 April 2021 |archive-date=16 April 2021 |archive-url=https://web.archive.org/web/20210416123152/https://www.washingtonian.com/2012/12/05/the-timekeeper-behind-americas-master-clock/ |url-status=live }}</ref> has been announcing the USNO time since 1978.<ref>{{cite news |title=Keeping time by rubidium at the Naval Observatory |publisher=[[NPR]] |url=https://www.npr.org/2014/07/06/329154831/keeping-time-by-rubidium-at-the-naval-observatory |access-date=2015-03-11 |archive-date=2015-03-29 |archive-url=https://web.archive.org/web/20150329005351/http://www.npr.org/2014/07/06/329154831/keeping-time-by-rubidium-at-the-naval-observatory |url-status=live }}</ref>
 
The voice announcements always begin with the local time (daylight or standard), and include a background of 1&nbsp;second ticks. Local time announcements are made on the minute, and 15, 30, and 45&nbsp;seconds after the minute. [[Coordinated Universal Time]] (UTC) is announced 5&nbsp;seconds after the local time.<ref>{{cite web |title=Telephone Time |series=Naval Oceanography Portal |website=www.usno.navy.mil |url=https://www.usno.navy.mil/USNO/time/telephone-time |access-date=2021-01-17 |archive-date=2021-01-22 |archive-url=https://web.archive.org/web/20210122024611/https://www.usno.navy.mil/USNO/time/telephone-time |url-status=live }}</ref> 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,<ref>{{cite web |url=http://tycho.usno.navy.mil/modem_time.html |title=USNO Master Clock via Modem |publisher=Tycho.usno.navy.mil |access-date=2011-07-27 |archive-date=2017-12-27 |archive-url=https://web.archive.org/web/20171227233738/http://tycho.usno.navy.mil/modem_time.html |url-status=live }}</ref> and provides time to the Global Positioning System.
 
==Instrument shop==
The United States Naval Observatory Instrument shop has been designing and manufacturing precise instrumentation since the early 1900s.<ref>{{Cite web |url=http://ad.usno.navy.mil/instshp/ |title=The USNO Instrument Shop |last=Fey |first=Alan L. |website=ad.usno.navy.mil |access-date=2018-11-08 |archive-date=2018-11-08 |archive-url=https://web.archive.org/web/20181108065539/http://ad.usno.navy.mil/instshp/ |url-status=live }}</ref>
 
== Publications ==
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* ''Observations made at the U.S. Naval Observatory'' ([http://doc.adsabs.harvard.edu/bib_abs.html?USNOO USNOO]) (v. 1–7: 1887–1893)
* ''Publications of the U.S. Naval Observatory'', Second Series ([http://doc.adsabs.harvard.edu/bib_abs.html?PUSNO PUSNO]) (v. 1–16: 1900–1949)
* ''U.S. Naval Observatory Circulars''<ref>{{cite web |author=Naval Meteorology and Oceanography Command |url=http://www.usno.navy.mil/USNO/astronomical-applications/publications/usno-special-pubs |title=U.S. Naval Observatory Special Publications — Naval Oceanography Portal |publisher=Usno.navy.mil |access-date=2011-07-27 |archive-date=2011-07-26 |archive-url=https://web.archive.org/web/20110726022411/http://www.usno.navy.mil/USNO/astronomical-applications/publications/usno-special-pubs |url-status=live }}</ref>
* ''[[The Astronomical Almanac]]''
* ''[[The Nautical Almanac]]''
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* {{Official website|https://www.cnmoc.usff.navy.mil/usno/}}
* [https://web.archive.org/web/20060321125122/http://www.cstone.net/~wmm/mfm-1847/index.html Transcription: Lieut. Matthew Fontaine Maury’s 1847 Letter to President John Quincy Adams on the many details of the United States National Observatory that was later called the "Navy" Observatory]
* [https://bibnum.obspm.fr/ark:/11287/2vckk Old photographs at the Paris Observatory] {{Webarchive|url=https://web.archive.org/web/20180426011725/https://bibnum.obspm.fr/ark:/11287/2vckk |date=2018-04-26 }}
 
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