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The United States Naval Observatory (USNO) is a scientific and military facility that produces
geopositioning Geopositioning is the process of determining or estimating the geographic position of an object or a person. Geopositioning yields a set of geographic coordinates (such as latitude and longitude) in a given map datum. Geographic positions may a ...
,
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the motion, movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navig ...
and
timekeeping Time is the continuous progression of existence that occurs in an apparently irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequence events, to compa ...
data for the
United States Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...
and the
United States Department of Defense The United States Department of Defense (DoD, USDOD, or DOD) is an United States federal executive departments, executive department of the federal government of the United States, U.S. federal government charged with coordinating and superv ...
. Established in 1830 as the Depot of Charts and Instruments, it is one of the oldest
scientific Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. Modern science is typically divided into twoor threemajor branches: the natural sciences, which stu ...
agencies in the
United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
, and remains the country's leading facility for astronomical and timing data. 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— ...
Washington, D.C. Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city and federal district of the United States. The city is on the Potomac River, across from Virginia, and shares land borders with ...
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 ...
. 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, geophysics, oceanography and volcanology are examples of disciplines for which observatories have been constructed. Th ...
located in an urban area. In 1893, in an effort to escape
light pollution Light pollution is the presence of any unwanted, inappropriate, or excessive artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting sources, during the ...
, it was relocated from
Foggy Bottom Foggy Bottom is a neighborhood of Washington, D.C., United States, located in the city's northwest quadrant. It stretches west of the White House towards the Potomac River, north of the National Mall, east of Georgetown, south of the West ...
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. 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 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 wi ...
. 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 sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by accretion onto a supermassive black hole with a mass rangi ...
s for
astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other Astronomical object, celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, th ...
and
geodesy Geodesy or geodetics is the science of measuring and representing the Figure of the Earth, geometry, Gravity of Earth, gravity, and Earth's rotation, spatial orientation of the Earth in Relative change, temporally varying Three-dimensional spac ...
with numerous global collaborators (
IERS The International Earth Rotation and Reference Systems Service (IERS), formerly the International Earth Rotation Service, is the body responsible for maintaining global time and reference frame standards, notably through its Earth Orientation P ...
), in order to produce
Earth orientation parameters In geodesy and astrometry, earth orientation parameters (EOP) describe irregularities in the rotation of planet Earth. EOP provide the rotational transform from the International Terrestrial Reference System (ITRS) to the International Celestial ...
and to realize the
celestial reference system In astronomy, coordinate systems are used for specifying position (geometry), positions of astronomical object, celestial objects (natural satellite, satellites, planets, stars, galaxy, galaxies, etc.) relative to a given reference frame, based o ...
( ICRF). Aside from its scientific mission, since the 1970s 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 ranking office in the Executive branch of the United States government, executive branch of the U.S. federal government, after the president of the United States, and ranks f ...
.


History

President
John Quincy Adams John Quincy Adams (; July 11, 1767 – February 23, 1848) was the sixth president of the United States, serving from 1825 to 1829. He previously served as the eighth United States secretary of state from 1817 to 1825. During his long diploma ...
, 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 The Secretary of the Navy (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 within the United States Department of Defense. On Mar ...
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 governor of the Florida Territory. 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, 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 The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...
's
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), and the time at t ...
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'' (1980 film), a 1980 Israeli film * ''Transit'' (1986 film), a Canadian short film * ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countrie ...
of
star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s across the meridian. It opened in 1844 in
Foggy Bottom Foggy Bottom is a neighborhood of Washington, D.C., United States, located in the city's northwest quadrant. It stretches west of the White House towards the Potomac River, north of the National Mall, east of Georgetown, south of the West ...
, north of the site of the
Lincoln Memorial The Lincoln Memorial is a List of national memorials of the United States, U.S. national memorial honoring Abraham Lincoln, the List of presidents of the United States, 16th president of the United States, located on the western end of the Nati ...
and west of the
White House The White House is the official residence and workplace of the president of the United States. Located at 1600 Pennsylvania Avenue Northwest (Washington, D.C.), NW in Washington, D.C., it has served as the residence of every U.S. president ...
. 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 National Register of Historic Places (NRHP) is the Federal government of the United States, United States federal government's official United States National Register of Historic Places listings, list of sites, buildings, structures, Hist ...
.


The time ball

The first superintendent was Navy Commander M.F. Maury. Maury had the world's first vulcanized
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 ...
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 Cambridge ( ) is a city in Middlesex County, Massachusetts, United States. It is a suburb in the Greater Boston metropolitan area, located directly across the Charles River from Boston. The city's population as of the 2020 United States census, ...
as a separate organization. In 1866, it was moved to
Washington, D.C. Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city and federal district of the United States. The city is on the Potomac River, across from Virginia, and shares land borders with ...
, 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. 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 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 The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...
, 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 A transit of Venus takes place when Venus passes directly between the Sun and the Earth (or any other superior planet), becoming visible against (and hence obscuring a small portion of) the solar disk. During a transit, Venus is visible as ...
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 film as the primary medium for capturing images in photography. These plates, made of metal or glass and coated with a light-sensitive emulsion, were integral to early photographic processes such as heliography, d ...
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, 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 and 40 inch refractors

The telescope used for the discovery of the
Moons of Mars The two natural satellite, moons of Mars (planet), Mars are Phobos (moon), Phobos and Deimos (moon), Deimos. They are irregular in shape. Both were discovered by American astronomer Asaph Hall in August 1877 and are named after the Greek mytholo ...
was the 26 inch (66 cm)
refractor A refracting telescope (also called a refractor) is a type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope). The refracting telescope design was originally used in spyglasses and ...
telescope, then located at
Foggy Bottom Foggy Bottom is a neighborhood of Washington, D.C., United States, located in the city's northwest quadrant. It stretches west of the White House towards the Potomac River, north of the National Mall, east of Georgetown, south of the West ...
, 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 A Ritchey–Chrétien telescope (RCT or simply RC) is a specialized variant of the Cassegrain telescope that has a hyperboloid, hyperbolic primary mirror and a hyperbolic secondary mirror designed to eliminate off-axis optical errors (Coma (optic ...
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 ...
and the space-borne
Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...
. Because of
light pollution Light pollution is the presence of any unwanted, inappropriate, or excessive artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting sources, during the ...
in the
Washington metropolitan area The Washington metropolitan area, also referred to as the National Capital Region, Greater Washington, or locally as the DMV (short for Washington, D.C., District of Columbia, Maryland, and Virginia), is the metropolitan area comprising Washing ...
, USNO relocated the 40 inch telescope to
Flagstaff, Arizona Flagstaff ( ), known locally as Flag, is the county seat of Coconino County, Arizona, in the southwestern United States. As of the 2020 United States census, the city's population was 76,831. Flagstaff is the principal city of the Coconino Cou ...
. 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 The Navy Precision Optical Interferometer (NPOI) is an American astronomical interferometer, with the world's largest baselines, operated by the Naval Research Laboratory (NRL). Until the end of 2022, it was operated by a consortium that included ...
.


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 corporation headquartered in Denver, Denver, Colorado. Founded in 1851 as the New York and Mississippi Valley Printing Telegraph Company in Rochester, New York, the co ...
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 Wireless communication (or just wireless, when the context allows) is the transfer of information (''telecommunication'') between two or more points without the use of an electrical conductor, optical fiber or other continuous guided transm ...
receivers. In November 1913 the
Paris Observatory The Paris Observatory (, ), a research institution of the Paris Sciences et Lettres University, is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world. Its historic building is on the Left Ban ...
, using the
Eiffel Tower The Eiffel Tower ( ; ) 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 from 1887 to 1889. Locally nicknamed "''La dame de fe ...
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, or simply Arlington, is a County (United States), county in the U.S. state of Virginia. The county is located in Northern Virginia on the southwestern bank of the Potomac River directly across from Washington, D.C., the nati ...
. The U.S. Naval Observatory in Washington continues to be a major authority in the areas of
Precise Time and Time Interval Precise Time and Time Interval (PTTI) is a United States Department of Defense, Department of Defense United States Armed Forces, military and Global Positioning System Technical standard, standard which details a mechanism and waveform for distrib ...
, Earth orientation,
astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other Astronomical object, celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, th ...
, and celestial observation. In collaboration with many national and international scientific establishments, it determines the timing and astronomical data required for accurate
navigation Navigation is a field of study that focuses on the process of monitoring and controlling the motion, movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navig ...
,
astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other Astronomical object, celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, th ...
, and fundamental
astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...
, and calculation methods — and distributes this information (such as
star catalogs An astronomical catalogue is a list or tabulation of astronomical objects, typically grouped together because they share a common type, morphology, origin, means of detection, or method of discovery. Astronomical catalogs are usually the result of ...
) on-line and in the annual publications '' The Astronomical 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 ...
''. 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 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 by the United States Air Force on 22 February 1978. ...
constellation run by the
United States Space Force The United States Space Force (USSF) is the space force branch of the United States Department of Defense. It is one of the six United States Armed Forces, armed forces of the United States and one of the eight uniformed services of the Unite ...
. The alternate Master Clock time service continues to operate 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, Col ...
in
Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...
.


Departments

In 1990 two departments were established:
Orbital Mechanics Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to rockets, satellites, and other spacecraft. The motion of these objects is usually calculated from Newton's laws of motion and the law of universal ...
and Astronomical Applications, with the Nautical Almanac Office a division in Astronomical Applications. The
Orbital Mechanics Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to rockets, satellites, and other spacecraft. The motion of these objects is usually calculated from Newton's laws of motion and the law of universal ...
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. 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
Flagstaff, Arizona Flagstaff ( ), known locally as Flag, is the county seat of Coconino County, Arizona, in the southwestern United States. As of the 2020 United States census, the city's population was 76,831. Flagstaff is the principal city of the Coconino Cou ...
, NOFS 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
vice president of the United States The vice president of the United States (VPOTUS) is the second-highest ranking office in the Executive branch of the United States government, executive branch of the U.S. federal government, after the president of the United States, and ranks f ...
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 i ...
. 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 the
chief of naval operations The chief of naval operations (CNO) is the highest-ranking officer of the United States Navy. The position is a statutory office () held by an Admiral (United States), admiral who is a military adviser and deputy to the United States Secretary ...
.


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. * The primary facility, in Washington, D.C. maintains 57  HP/ Agilent/ Symmetricom 5071A-001 high performance
cesium Caesium (IUPAC spelling; also spelled cesium in American English) is a chemical element; it has 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 ...
atomic clocks and 24  hydrogen masers. * 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, Col ...
, maintains 12 cesium clocks and 3 masers. The observatory also operates four
rubidium Rubidium is a chemical element; it has Symbol (chemistry), 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 ...
atomic fountain An atomic fountain measures an atomic hyperfine transition by letting a cloud of laser-cooled atoms fall through an interaction region under the influence of gravity. The atomic cloud is cooled and pushed upwards by a counter-propagating lasers in ...
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 network, global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a internetworking, network of networks ...
, 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 (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communicat ...
(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 Astronomical Almanac'' * ''
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 Air Almanac'' * '' Astronomical Phenomena''


See also

Astronomy and observatories * dark-sky movement *
List of astronomical observatories This is a partial list of astronomical observatories ordered by name, along with initial dates of operation (where an accurate date is available) and location. The list also includes a final year of operation for many observatories that are no lon ...
* The Old Naval Observatory * USNO Flagstaff Station Technology and technical resources *
Coordinated Universal Time Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communicat ...
(UTC) * Naval Observatory Vector Astrometry Subroutines * railroad chronometer *
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 ...
*
Time signal A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks; however, au ...
* time service radio stations WWV, WWVH, & WWVB USNO personnel * Rear Admiral Samuel P. Carter * Lieutenant James Melville Gilliss * Lieutenant Louis M. Goldsborough * Commander
Matthew Fontaine Maury Matthew Fontaine Maury (January 14, 1806February 1, 1873) was an American oceanographer and naval officer, serving the United States and then joining the Confederacy during the American Civil War. He was nicknamed "Pathfinder of the Seas" and ...
* astronomer P. Kenneth Seidelmann * director Gernot M. R. Winkler


Notes


References


Further reading

* * (British edition).


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" Observatory

Old photographs at the Paris Observatory
{{Authority control Naval Observatory Naval Observatory Naval Observatory Naval Observatory Naval Observatory Time balls 1830 establishments in Washington, D.C. National Register of Historic Places in Washington, D.C. Astrometry Geodesy organizations