The United States Naval Observatory (USNO) is a scientific and military facility that produces

geopositioning Geopositioning, also known as geotracking, geolocalization, geolocating, geolocation, or geoposition fixing, is the process of determining or estimating the geographic position of an object. Geopositioning yields a set of geographic coordinates ...

navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...

and

timekeeping Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to co ...

data for the

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

and the

United States Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national secu ...

. Established in 1830 as the Depot of Charts and Instruments, it is one of the oldest

scientific Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence for ...

agencies in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

, and remains the country's leading authority for astronomical and timing data for all purposes. The observatory is located in

Northwest The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each sep ...

Washington, D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, ...

at the northwestern end of

Embassy Row Embassy Row is the informal name for a section of Northwest Washington, D.C. with a high concentration of embassies, diplomatic missions, and diplomatic residences. It spans Massachusetts Avenue N.W. between 18th and 35th street, bounded by ...

. It is among the few pre-20th century

astronomical observatories An observatory is a location used for observing terrestrial, marine, or celestial events. Astronomy, climatology/meteorology, geophysical, oceanography and volcanology are examples of disciplines for which observatories have been constructed. His ...

located in an urban area; initially located in

Foggy Bottom Foggy Bottom is one of the oldest late 18th- and 19th-century neighborhoods in Washington, D.C., located west of the White House and downtown Washington, in the Northwest quadrant. It is bounded roughly by 17th Street NW to the east, Rock C ...

near the city's center, it was relocated to its current location in 1893 to escape

light pollution Light pollution is the presence of unwanted, inappropriate, or excessive use of artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting, during the day ...

. 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. Its achievements including providing data for the first radio time signals, constructing some of the earliest and most accurate telescopes of their kind, and helping develop

universal time Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with ...

. The Naval Observatory performs radio

VLBI Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth or in space. T ...

-based positions of

quasar A quasar is an extremely Luminosity, luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a m ...

s for

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. His ...

and

geodesy Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivale ...

with numerous global collaborators ( IERS), in order to produce Earth orientation parameters and to realize the

celestial reference system Astronomical coordinate systems are organized arrangements for specifying positions of satellites, planets, stars, galaxies, and other celestial objects relative to physical reference points available to a situated observer (e.g. the true hor ...

( ICRF). Aside from its scientific mission, the Naval Observatory campus hosts the official residence of the

vice president of the United States The vice president of the United States (VPOTUS) is the second-highest officer in the executive branch of the U.S. federal government, after the president of the United States, and ranks first in the presidential line of succession. The vice ...

History

Early presidential astronomical interest

President

John Quincy Adams John Quincy Adams (; July 11, 1767 – February 23, 1848) was an American statesman, diplomat, lawyer, and diarist who served as the sixth president of the United States, from 1825 to 1829. He previously served as the eighth United States S ...

, 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 at that time. He spent many nights at the observatory, watching and charting the stars, which had always been one of Adams' interests.

Establishment as an optical equipment depot

Established by order of the

United States Secretary of the Navy The secretary of the Navy (or SECNAV) is a statutory officer () and the head (chief executive officer) of the United States Department of the Navy, Department of the Navy, a military department (component organization) within the United States D ...

John Branch John Branch Jr. (November 4, 1782January 4, 1863) was an American politician who served as U.S. Senator, Secretary of the Navy, the 19th Governor of the state of North Carolina, and was the sixth and last territorial governor of Florida. B ...

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 Louis Malesherbes Goldsborough (February 18, 1805 – February 20, 1877) was a rear admiral in the United States Navy during the American Civil War. He held several sea commands during the Civil War, including that of the North Atlantic Blockadi ...

, with an annual budget of $330; its primary function was the restoration, repair, and rating of navigational instruments.

Federal 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

marine chronometer A marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation. It is used to determine longitude by comparing Greenwich Mean Time (GMT), or in the modern ...

s, charts, and other navigational equipment. It

calibrated In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known ...

ships' chronometers by timing the

transit Transit may refer to: Arts and entertainment Film * ''Transit'' (1979 film), a 1979 Israeli film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the world * ''Transit'' (2006 film), a 2006 ...

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s across the

meridian Meridian or a meridian line (from Latin ''meridies'' via Old French ''meridiane'', meaning “midday”) may refer to Science * Meridian (astronomy), imaginary circle in a plane perpendicular to the planes of the celestial equator and horizon * ...

. It opened in 1844 in

, north of the present site of the

Lincoln Memorial The Lincoln Memorial is a U.S. national memorial built to honor the 16th president of the United States, Abraham Lincoln. It is on the western end of the National Mall in Washington, D.C., across from the Washington Monument, and is in the ...

and west of the

White House The White House is the official residence and workplace of the president of the United States. It is located at 1600 Pennsylvania Avenue NW in Washington, D.C., and has been the residence of every U.S. president since John Adams in 1800. ...

(see:

Old Naval Observatory The Old Naval Observatory is a historic site at 23rd and E Street in Northwest, Washington, D.C. It is where the United States Naval Observatory was located from 1844 to 1893, when it moved to its present grounds. The original observatory build ...

). The observatory moved to its present location in 1893 located on a 2000 foot circle of land atop "Observatory Hill", overlooking

Massachusetts Avenue Massachusetts Avenue may refer to: * Massachusetts Avenue (metropolitan Boston), Massachusetts ** Massachusetts Avenue (MBTA Orange Line station), a subway station on the MBTA Orange Line ** Massachusetts Avenue (MBTA Silver Line station), a stati ...

. The facilities were listed on the

National Register of Historic Places The National Register of Historic Places (NRHP) is the United States federal government's official list of districts, sites, buildings, structures and objects deemed worthy of preservation for their historical significance or "great artistic v ...

in 2017.

The iconic time-ball

The first superintendent was Navy Commander M.F. Maury. Maury had the world's first

vulcanized Vulcanization (British: Vulcanisation) is a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to inclu ...

time ball A time ball or timeball is a time-signalling device. It consists of a large, painted wooden or metal ball that is dropped at a predetermined time, principally to enable navigators aboard ships offshore to verify the setting of their marine chron ...

, created to his specifications by

Charles Goodyear Charles Goodyear (December 29, 1800 – July 1, 1860) was an American self-taught chemist and manufacturing engineer who developed vulcanized rubber, for which he received patent number 3633 from the United States Patent Office on June 15, 1844. ...

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 Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...

to ring the alarm bells in all of the Washington, D.C. firehouses three times a day.

The Nautical Almanac Office

In 1849 the Nautical Almanac Office (NAO) was established in

Cambridge, Massachusetts Cambridge ( ) is a city in Middlesex County, Massachusetts, United States. As part of the Boston metropolitan area, the cities population of the 2020 U.S. census was 118,403, making it the fourth most populous city in the state, behind Boston, ...

as a separate organization. It was moved to

in 1866, originally operating near Fort Myer. It relocated to the U.S. Naval Observatory grounds in 1893. On 20 September 1894, the NAO became a "branch" of USNO; however, it remained autonomous for several years afterward.

Measuring the astonomical unit

An early scientific duty assigned to the Observatory was the U.S. contribution to the definition of the

Astronomical Unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...

, 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 frameless, upright=0.5 A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and a superior planet, becoming visible against (and hence obscuring a small portion of) the solar disk. During a trans ...

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 plate Photographic plates preceded photographic film as a capture medium in photography, and were still used in some communities up until the late 20th century. The light-sensitive emulsion of silver salts was coated on a glass plate, typically thinn ...

s 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 Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

, 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 new 26 inch and 40 inch refractors

The telescope used for the discovery of the

Moons of Mars The two moons of Mars are Phobos and Deimos. They are irregular in shape. Both were discovered by American astronomer Asaph Hall in August 1877 and are named after the Greek mythological twin characters Phobos (fear and panic) and Deimos (te ...

was the 26 inch (66 cm)

refractor A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens (optics), lens as its objective (optics), objective to form an image (also referred to a dioptrics, dioptric telescope). The refracting telescope d ...

(a telescope containing only lenses), then located at

, Washington, DC. In 1893 it was moved to the present location. In 1934, the last (then) large telescope to be 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 A Ritchey–Chrétien telescope (RCT or simply RC) is a specialized variant of the Cassegrain telescope that has a hyperbolic primary mirror and a hyperbolic secondary mirror designed to eliminate off-axis optical errors (coma). The RCT has a wi ...

design has since become the ''de facto'' optical design for nearly all major telescopes, including the famed

Keck telescopes The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when co ...

and the space-borne

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

. Because of

in the

Washington metropolitan area The Washington metropolitan area, also commonly referred to as the National Capital Region, is the metropolitan area centered on Washington, D.C. The metropolitan area includes all of Washington, D.C. and parts of the states of Maryland, Virgin ...

, USNO relocated the 40 inch telescope to

Flagstaff, Arizona Flagstaff ( ) is a city in, and the county seat of, Coconino County, Arizona, Coconino County in northern Arizona, in the southwestern United States. In 2019, the city's estimated population was 75,038. Flagstaff's combined metropolitan area has ...

. 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 Kaj Aage Gunnar Strand (27 February 1907 – 31 October 2000) was a Danish astronomer who worked in Denmark and the United States. He was Scientific Director of the U.S. Naval Observatory from 1963 to 1977. He specialized in astrometry, espe ...

Astrometric Reflector" was built; it saw light at Flagstaff in 1964. USNO continues to maintain its dark-sky observatory,

NOFS The United States Naval Observatory Flagstaff Station (NOFS), is an astronomical observatory near Flagstaff, Arizona, US. It is the national dark-sky observing facility under the United States Naval Observatory (USNO). NOFS and USNO combine a ...

, near Flagstaff. This facility now oversees the

Navy Precision Optical Interferometer The Navy Precision Optical Interferometer (NPOI) is an American astronomical interferometer, with the world's largest baselines, operated by the Naval Observatory Flagstaff Station (NOFS) in collaboration with the Naval Research Laboratory (NRL) ...

. The alternate Master Clock, discussed below, continues to operate at

Schriever Air Force Base Schriever Space Force Base, previously Schriever Air Force Base, Falcon Air Force Base, and Falcon Air Force Station, is a base of the United States Space Force located approximately east of Peterson Space Force Base near Colorado Springs in ...

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...

History of the time service

By the early 1870s the USNO daily noon-time signal was distributed electrically, nationwide, via the

Western Union The Western Union Company is an American multinational financial services company, headquartered in Denver, Colorado. Founded in 1851 as the New York and Mississippi Valley Printing Telegraph Company in Rochester, New York, the company chang ...

Telegraph Company. Time was also “sold” to the railroads and was used in conjunction with

railroad chronometer A railroad chronometer or railroad standard watch is a specialized timepiece that once was crucial for safe and correct operation of trains in many countries. A system of timetable and train order, which relied on highly accurate timekeeping, was ...

s 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 Wireless communication (or just wireless, when the context allows) is the transfer of information between two or more points without the use of an electrical conductor, optical fiber or other continuous guided medium for the transfer. The most ...

receivers. In November 1913 the

Paris Observatory The Paris Observatory (french: Observatoire de Paris ), a research institution of the Paris Sciences et Lettres University, is the foremost astronomical observatory of France, and one of the largest astronomical centers in the world. Its histor ...

, using the

Eiffel Tower The Eiffel Tower ( ; french: links=yes, tour Eiffel ) is a wrought-iron lattice tower on the Champ de Mars in Paris, France. It is named after the engineer Gustave Eiffel, whose company designed and built the tower. Locally nicknamed "'' ...

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 Arlington County is a county in the Commonwealth of Virginia. The county is situated in Northern Virginia on the southwestern bank of the Potomac River directly across from the District of Columbia, of which it was once a part. The county is ...

. 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 Precise Time and Time Interval (PTTI) is a Department of Defense military and Global Positioning System standard which details a mechanism and waveform for distributing highly accurate timing information.Earth orientation,

, and celestial observation. In collaboration with many national and international scientific establishments, it determines the timing and astronomical data required for accurate

, and fundamental

astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...

, and calculation methods — and distributes this information (such as star catalogs) on-line and in the annual publications ''

The Astronomical Almanac ''The Astronomical Almanac''The ''Astronomical Almanac'' for the Year 2015, (United States Naval Observatory/Nautical Almanac Office, 2014) . is an almanac published by the United States Naval Observatory (USNO) and His Majesty's Nautical Almanac ...

'' and ''

The Nautical Almanac ''The Nautical Almanac'' has been the familiar name for a series of official British almanacs published under various titles since the first issue of ''The Nautical Almanac and Astronomical Ephemeris'', for 1767: this was the first nautical alm ...

''. The general public knows about the “Master Clock”, the observatory’s highly accurate ensemble of

atomic clock An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...

s, and its one-off time-ball re-enactment for the year-2000 celebration. The site houses the largest astronomy library in the United States (and the largest astrophysical periodicals collection in the world). 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 Gernot Maria Rudolph Winkler (October 17, 1922 – April 30, 2016) was responsible for the Time Service Department of the United States Naval Observatory (USNO) from 1966 to 1996. Winkler oversaw the introduction of caesium beam-based Coordinat ...

initiated the "Master Clock" service that the USNO still operates, and which provides precise time to the

GPS satellite GPS satellite blocks are the various production generations of the Global Positioning System (GPS) used for satellite navigation. The first satellite in the system, Navstar 1, was launched on 22 February 1978. The GPS satellite constellatio ...

constellation run by the

United States Space Force The United States Space Force (USSF) is the space service branch of the U.S. Armed Forces, one of the eight U.S. uniformed services, and the world's only independent space force. Along with its sister branch, the U.S. Air Force, the Space ...

Departments

In 1990 two departments were established:

Orbital Mechanics Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to the practical problems concerning the motion of rockets and other spacecraft. The motion of these objects is usually calculated from Newton's laws of ...

and Astronomical Applications, with the

Nautical Almanac A nautical almanac is a publication describing the positions of a selection of celestial bodies for the purpose of enabling navigators to use celestial navigation to determine the position of their ship while at sea. The Almanac specifies for ea ...

Office a division in Astronomical Applications. The

Department operated under

P. Kenneth Seidelmann P. is an abbreviation or acronym that may refer to: * Page (paper), where the abbreviation comes from Latin ''pagina'' * Paris Herbarium, at the ''Muséum national d'histoire naturelle'' * ''Pani'' (Polish), translating as Mrs. * The ''Pacific Repo ...

until 1994, when the department was abolished and its functions transferred to a group within the Astronomical Applications Department. In 2010, USNO's astronomical 'department' known as the Naval 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 outside

performs its national, Celestial Reference Frame (CRF) mission under dark skies in that region.

Official residence of the vice president of the United States

A house situated on the grounds of the observatory, at Number One Observatory Circle, has been the official residence of the

since 1974. It is protected by tight security control enforced by the

Secret Service A secret service is a government agency, intelligence agency, or the activities of a government agency, concerned with the gathering of intelligence data. The tasks and powers of a secret service can vary greatly from one country to another. For ...

. The house is separated from the Naval Observatory. It formerly served as the residence of the observatory's superintendent, and later was the residence of the

chief of naval operations The chief of naval operations (CNO) is the professional head of the United States Navy. The position is a statutory office () held by an admiral who is a military adviser and deputy to the secretary of the Navy. In a separate capacity as a memb ...

, and finally the

vice president A vice president, also director in British English, is an officer in government or business who is below the president (chief executive officer) in rank. It can also refer to executive vice presidents, signifying that the vice president is on t ...

Time service

The U.S. Naval Observatory operates two “Master Clock” facilities, one in Washington, DC, and the other at Schriever SFB near

Colorado Springs, CO Colorado Springs is a home rule municipality in, and the county seat of, El Paso County, Colorado, United States. It is the largest city in El Paso County, with a population of 478,961 at the 2020 United States Census, a 15.02% increase since ...

. * The primary facility, in Washington, D.C. maintains 57 HP/

Agilent Agilent Technologies, Inc. is an American life sciences company that provides instruments, software, services, and consumables for the entire laboratory workflow. Its global headquarters is located in Santa Clara, California. Agilent was establi ...

Symmetricom Symmetricom, Inc. (NASDAQ: SYMM) (acquired by Microsemi in 2013, then acquired by Microchip in 2018) develops, manufactures, and supplies timekeeping technology to customers in industry and government worldwide that require extremely precise synchro ...

5071A-001 high performance

cesium Caesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that ar ...

atomic clocks and 24

hydrogen maser A hydrogen maser, also known as hydrogen frequency standard, is a specific type of maser that uses the intrinsic properties of the hydrogen atom to serve as a precision frequency reference. Both the proton and electron of a hydrogen atom have sp ...

s. * The alternate facility, at

Schriever Space Force Base Schriever Space Force Base, previously Schriever Air Force Base, Falcon Air Force Base, and Falcon Air Force Station, is a base of the United States Space Force located approximately east of Peterson Space Force Base near Colorado Springs in ...

, maintains 12 cesium clocks and 3 masers. The observatory also operates four

rubidium Rubidium is the chemical element with the symbol Rb and atomic number 37. It is a very soft, whitish-grey solid in the alkali metal group, similar to potassium and caesium. Rubidium is the first alkali metal in the group to have a density higher ...

atomic fountain An atomic fountain is a cloud of atoms that is tossed upwards in the Earth's gravitational field by lasers. If it were visible, it would resemble the water in a fountain. While weightless in the toss, the atoms are measured to set the frequency o ...

clocks, which have a stability reaching 7. The observatory plans to build several more of this type for use at its two facilities. 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. The U.S. Naval Observatory provides public time service via 26 NTP servers on the public

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

, and via telephone voice announcements: * +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 (1928–1993) has been announcing the USNO time since 1978. 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 Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used ...

(UTC) is announced 5 seconds after the local time. 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, 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.

Publications

* ''Astronomical Observations made at the U.S. Naval Observatory''
USNOA
(v. 1–6: 1846–1867) * ''Astronomical and Meteorological Observations made at the U.S. Naval Observatory''

(v. 1–22: 1862–1880) * ''Observations made at the U.S. Naval Observatory''

(v. 1–7: 1887–1893) * ''Publications of the U.S. Naval Observatory'', Second Series

(v. 1–16: 1900–1949) * ''U.S. Naval Observatory Circulars'' * ''

'' * ''

'' * '' The Air Almanac'' * '' Astronomical Phenomena''

Notes

References

External links

*
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" ObservatoryOld photographs at the Paris Observatory
{{Authority control

Naval Observatory 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. Established in 1 ...

Time balls 1830 establishments in Washington, D.C. National Register of Historic Places in Washington, D.C. Astrometry Geodesy organizations