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41-521: The observatory is located in Northwest Washington, D.C. at the northwestern end of Embassy Row . It is among the few pre-20th century astronomical observatories located in an urban area. In 1893, in an effort to escape light pollution , it was relocated from Foggy Bottom near the city's center, to its Northwest Washington, D.C. location. The USNO has conducted significant scientific studies throughout its history, including measuring

82-560: A 24-hour clock) or 1200 ( military time ). Solar noon is the time when the Sun appears to contact the local celestial meridian . This is when the Sun reaches its apparent highest point in the sky, at 12 noon apparent solar time and can be observed using a sundial . The local or clock time of solar noon depends on the date, longitude , and time zone , with Daylight Saving Time tending to place solar noon closer to 1:00pm. The word noon

123-438: A major authority in the areas of Precise Time and Time Interval , Earth orientation , astrometry , and celestial observation. In collaboration with many national and international scientific establishments, it determines the timing and astronomical data required for accurate navigation , astrometry , and fundamental astronomy , and calculation methods — and distributes this information (such as star catalogs ) on-line and in

164-450: A number of countries since 1639 resulted in a progressively more accurate definition of the AU . Relying strongly on photographic methods, the naval observers returned 350  photographic plates in 1874, and 1,380 measurable plates in 1882. The results of the surveys conducted simultaneously from several locations around the world (for each of the two transits) produced a final value of

205-560: A stability reaching 7 × 10. 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

246-483: Is "improper" based on the Latin meaning (a.m. stands for ante meridiem and p.m. for post meridiem , meaning "before midday" and "after midday" respectively), digital clocks are unable to display anything else, and an arbitrary decision must be made. An earlier standard of indicating noon as "12M" or "12m" (for "meridies"), which was specified in the U.S. GPO Government Style Manual , has fallen into relative obscurity;

287-950: Is 48.33% male, and 51.67% female. There are 146,397 households, with 57,445 being family households, and 88,951 being non-family households. Northwest Washington, D.C., includes the following 58 neighborhoods: Northwest contains many college campuses, including American University , George Washington University , Georgetown University , Howard University , and the University of the District of Columbia . Northwest also contains many primary and secondary schools, many of which are public schools administered by DCPS (District of Columbia Public Schools). There are 44 DCPS institutions in Northwest, as well as many private schools, including St. John's College High School , Sidwell Friends School , Gonzaga College High School , Duke Ellington School of

328-765: Is bounded by the Potomac River on the west, Western Avenue and Eastern Avenue to the north, North Capitol Street to the east, and the National Mall to the south. Other principal roads include Connecticut Avenue between Chevy Chase and the White House, Wisconsin Avenue between Friendship Heights and Georgetown, Pennsylvania Avenue between Georgetown and the Capitol , K Street , Massachusetts Avenue (home to Embassy Row), and 16th Street . Northwest

369-471: Is derived from Latin nona hora , the ninth canonical hour of the day, in reference to the Western Christian liturgical term Nones (liturgy) , (number nine), one of the seven fixed prayer times in traditional Christian denominations . The Roman and Western European medieval monastic day began at 6:00 a.m. (06:00) at the equinox by modern timekeeping, so the ninth hour started at what

410-426: Is now 3:00 p.m. (15:00) at the equinox. In English, the meaning of the word shifted to midday and the time gradually moved back to 12:00 local time – that is, not taking into account the modern invention of time zones. The change began in the 12th century and was fixed by the 14th century. Solar noon , also known as the local apparent solar noon and Sun transit time (informally high noon ),

451-620: Is served by all six lines of the Washington Metro : the Orange , Silver , Red , Blue , Yellow , and Green Lines . Many Metrobus lines run through the quadrant, as well as the DC Circulator . Noon Noon (or midday ) is 12 o'clock in the daytime . It is written as 12 noon , 12:00 m. (for meridiem , literally 12:00 midday), 12 p.m. (for post meridiem , literally "after midday"), 12 pm , or 12:00 (using

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492-539: Is the moment when the Sun contacts the observer's meridian ( culmination or meridian transit ), reaching its highest position above the horizon on that day and casting the shortest shadow. This is also the origin of the terms ante meridiem (a.m.) and post meridiem (p.m.), as noted below. The Sun is directly overhead at solar noon at the Equator on the equinoxes , at the Tropic of Cancer ( latitude 23°26′09.8″ N) on

533-591: Is the northwestern quadrant of Washington, D.C. , the capital of the United States, and is located north of the National Mall and west of North Capitol Street . It is the largest of the four quadrants of the city (NW, NE , SW and SE ), and it includes the central business district , the Federal Triangle , and the museums along the northern side of the National Mall, as well as many of

574-735: The June solstice and at the Tropic of Capricorn (23°26′09.8″ S) on the December solstice . In the Northern Hemisphere , north of the Tropic of Cancer, the Sun is due south of the observer at solar noon; in the Southern Hemisphere , south of the Tropic of Capricorn, it is due north. The elapsed time from the local solar noon of one day to the next is exactly 24 hours on only four instances in any given year. This occurs when

615-819: The Nautical Almanac Office a division in Astronomical Applications. The 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. 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

656-586: The Secret Service . The house is separated from the Naval Observatory. Before serving as the vice president's residence, it was that of the observatory's superintendent, and later the chief of naval operations . 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 observatory also operates four rubidium atomic fountain clocks, which have

697-576: The celestial reference system ( 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 . President John Quincy Adams , who in 1825 signed the bill for the creation of a national observatory just before leaving presidential office, had intended for it to be called the National Observatory. The names "National Observatory" and "Naval Observatory" were both used for 10 years, until

738-550: The solar parallax , after adjustments, of 8.809″, with a probable error of 0.0059″, yielding a U.S.-determined Earth-Sun distance of 92,797,000 mi (149,342,000 km), with a probable error of 59,700 mi (96,100 km). The calculated distance was a significant improvement over several previous estimates. The telescope used for the discovery of the Moons of Mars was the 26 inch (66 cm) refractor telescope, then located at Foggy Bottom , Washington, DC. In 1893 it

779-664: The 20th century, the service was broadcast by radio, with Arlington time signal available to those with wireless receivers. In November 1913 the Paris Observatory , using the Eiffel Tower as an antenna , exchanged sustained wireless (radio) signals with the U.S. Naval Observatory to determine the exact difference of longitude between the two institutions, via an antenna in Arlington, Virginia . The U.S. Naval Observatory in Washington continues to be

820-722: The Arts , and Georgetown Day School , among others. The Capital One Arena , home of the Washington Wizards , the Washington Capitals , and the Georgetown Hoyas as well as the venue for many concerts and other events, is located in the District's Chinatown in Northwest. The National Cathedral , the White House , Rock Creek Park , and Embassy Row are also located in this quadrant. Northwest

861-411: The District's historic neighborhoods. Politically, Northwest is made up of parts of Wards 1, 2, 3, 4, 5, and 6, with Wards 1 and 3 being the only wards located entirely within the quadrant. The Northwest is the wealthiest quadrant of the city, particularly west of 16th Street . The population of Northwest is 340,531, based on the data collected in the latest U.S. Census Bureau release. The population

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902-816: The Secretary of the Navy officially adopted the latter. Adams had made protracted efforts to bring astronomy to a national level. He spent many nights at the observatory, watching and charting the stars, which had always been one of his interests. Established by order of the United States Secretary of the Navy John Branch on 6 December 1830 as the Depot of Charts and Instruments, the Observatory rose from humble beginnings: Placed under

943-442: The USNO in Washington. In the alpine woodlands above 7,000 feet altitude outside Flagstaff, Arizona , NOFS performs its national, Celestial Reference Frame (CRF) mission under dark skies in that region. A house situated on the grounds of the observatory, at Number One Observatory Circle, has been the official residence of the vice president of the United States since 1974. It is protected by tight security control enforced by

984-402: 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 (UTC) is announced 5 seconds after the local time. Upon connecting, only the second-marking ticks are heard for

1025-697: The annual publications The Astronomical Almanac and The Nautical Almanac . Former USNO director Gernot M. R. Winkler initiated the " Master clock " service that the USNO still operates, and which provides precise time to the GPS satellite constellation run by the United States Space Force . The alternate Master Clock time service continues to operate at Schriever Space Force Base in Colorado . In 1990 two departments were established: Orbital Mechanics and Astronomical Applications, with

1066-489: 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 , and via telephone voice announcements: The voice of actor Fred Covington (1928–1993) has been announcing

1107-404: 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. 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

1148-465: The effects of Earth's obliquity of ecliptic and its orbital speed around the Sun offset each other. These four days for the current epoch are centered on 11 February, 13 May, 26 July, and 3 November. It occurs at only one particular line of longitude in each instance. This line varies year to year, since Earth's true year is not an integer number of days. This event time and location also varies due to Earth's orbit being gravitationally perturbed by

1189-603: The exact time. By the end of the American Civil War, the Observatory's clocks were linked via telegraph to ring the alarm bells in all of the Washington, D.C. firehouses three times a day. The USNO held a one-off time-ball re-enactment for the year-2000 celebration. In 1849, the Nautical Almanac Office (NAO) was established in Cambridge, Massachusetts as a separate organization. In 1866, it

1230-541: 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. The United States Naval Observatory Instrument shop has been designing and manufacturing precise instrumentation since the early 1900s. Astronomy and observatories Technology and technical resources USNO personnel Northwest (Washington, D.C.) Northwest ( NW or N.W. )

1271-519: The past millennium. An early scientific duty assigned to the Observatory was the U.S. contribution to the definition of the Astronomical Unit , or the AU , which defines a standard mean distance between the Sun and the Earth. This was conducted under the auspices of the congressionally-funded U.S. Transit of Venus Commission. The astronomical measurements taken of the transit of Venus by

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1312-705: The planets. These four 24-hour days occur in both hemispheres simultaneously. The precise UTC times for these four days also mark when the opposite line of longitude, 180° away, experiences precisely 24 hours from local midnight to local midnight the next day. Thus, four varying great circles of longitude define from year to year when a 24-hour day (noon to noon or midnight to midnight) occurs. The two longest time spans from noon to noon occur twice each year, around 20 June (24 hours plus 13 seconds) and 21 December (24 hours plus 30 seconds). The shortest time spans occur twice each year, around 25 March (24 hours minus 18 seconds) and 13 September (24 hours minus 22 seconds). For

1353-531: The principal observatories of Europe with the mission to purchase telescopes and other scientific devices, and books. The observatory's primary mission was to care for the United States Navy 's marine chronometers , charts, and other navigational equipment. It calibrated ships' chronometers by timing the transit of stars across the meridian . It opened in 1844 in Foggy Bottom , north of

1394-507: The same reasons, solar noon and "clock noon" are usually not the same. The equation of time shows that the reading of a clock at solar noon will be higher or lower than 12:00 by as much as 16 minutes. Additionally, due to the political nature of time zones, as well as the application of daylight saving time , it can be off by more than an hour. In the US, noon is commonly indicated by 12 p.m., and midnight by 12 a.m. While some argue that such usage

1435-617: The site of the Lincoln Memorial and west of the White House . In 1893, the observatory moved to its current location in Northwest Washington, D.C. located on a 2000 foot circle of land atop "Observatory Hill", overlooking Massachusetts Avenue . In 2017, the facilities were listed on the National Register of Historic Places . The first superintendent was Navy Commander M.F. Maury . Maury had

1476-535: The space-borne Hubble Space Telescope . Because of light pollution in the Washington metropolitan area , USNO relocated the 40 inch telescope to Flagstaff, Arizona . A new Navy command, now called the USNO Flagstaff Station (NOFS), was established there. Those operations began in 1955. Within a decade, the Navy's largest telescope, the 61 inch " Kaj Strand Astrometric Reflector"

1517-485: 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 . The Naval Observatory performs radio VLBI -based positions of quasars for astrometry and geodesy with numerous global collaborators ( IERS ), in order to produce Earth orientation parameters and to realize

1558-461: The world's first vulcanized time ball , created to his specifications by Charles Goodyear for the U.S. Observatory. Placed into service in 1845, it was the first time ball in the United States and the 12th in the world. Maury kept accurate time by the stars and planets. The time ball was dropped every day except Sunday, precisely at the astronomically defined moment of mean solar noon ; this enabled all ships and civilians within sight to know

1599-660: 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 . By the early 1870s the USNO daily noon-time signal was distributed electrically, nationwide, via the Western Union Telegraph Company. Time was also "sold" to the railroads and was used in conjunction with railroad chronometers to schedule American rail transport. Early in

1640-501: Was moved to Washington, D.C. , 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

1681-413: Was moved to its Northwest DC location. In 1934, the largest optical telescope installed at USNO saw "first light". This 40 inch aperture instrument was also the second (and final) telescope made by famed optician, George Willis Ritchey . The Ritchey–Chrétien telescope design has since become the de facto optical design for nearly all major telescopes, including the famed Keck telescopes and

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