United States Naval Observatory

The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States, with a primary mission[1] to produce Positioning, Navigation and Timing (PNT)[2] for the United States Navy and the United States Department of Defense. Located in Northwest Washington, D.C. at the Northwestern end of Embassy Row, it is one of the pre-1900 astronomical observatories located in an urban area; at the time of its construction, it was far from the light pollution thrown off by the (then-smaller) city center. Former USNO director Gernot M. R. Winkler initiated the "Master Clock" service that the USNO still operates,[3] and which provides precise time to the GPS satellite constellation run by the United States Air Force. The USNO performs radio VLBI-based positions of quasars with numerous global collaborators, in order to produce Earth Orientation parameters.

Aside from its scientific mission, a house located within the Naval Observatory complex serves as the official residence of the Vice President of the United States.

U.S. Naval Observatory-seal
The Seal of the USNO with a quote from the Astronomicon, 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"


United States Naval Observatory.aerial view
Aerial view of the U.S. Naval Observatory

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.[4] The names "National Observatory" and "Naval Observatory" were both used for 10 years, until a ruling was passed to officially use the latter.[5] Adams had made protracted efforts to bring astronomy to a national level at that time.[6][7] He spent many nights at the observatory, watching and charting the stars, which had always been one of Adams' avocations.

Established by the order of the United States Secretary of the Navy John Branch on 6 December 1830 as the Depot of Charts and Instruments,[8] 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. It was made into a national observatory in 1842 via a federal law and a Congressional appropriation of $25,000. Lieutenant James Melville Gilliss was put in charge of "obtaining the instruments needed and books."[9] Lt. Gilliss visited the principal observatories of Europe with the mission to purchase telescopes and scientific devices and books.[10]

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. 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 in 1893 to its present location[11] on a 2000-foot circle of land atop Observatory Hill overlooking Massachusetts Avenue. These facilities were listed on the National Register of Historic Places in 2017.[12]

The first superintendent was Navy Commander Matthew Fontaine Maury. Maury had the world's first vulcanized time ball, created to his specifications by Charles Goodyear for the U.S. Observatory. It was the first time ball in the United States, being placed into service in 1845, 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, enabling all ships and civilians to know 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, and by the early 1870s the Observatory's daily noon-time signal was being distributed 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 the 20th century, the Arlington Time Signal broadcast this service to wireless receivers.

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, colocating with the U. S. Naval Observatory in 1893. On September 20, 1894, the NAO became a "branch" of USNO, however it remained autonomous for several years after this.[13]

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, 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 AU. Relying heavily 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 the solar parallax, after adjustments, of 8.809", with a probable error of 0.0059", yielding a U.S. defined Earth-Sun distance of 92,797,000 miles (149,342,000 km), with a probable error of 59,700 miles (96,100 km). This calculated distance was a significant improvement over several previous estimates.[14]

The telescope used for the discovery of the Moons of Mars was the 26-inch (66 cm) refractor (a telescope with a lens), then located at Foggy Bottom.[15] In 1893 it was moved to the present location.[16]

In November 1913 the Paris Observatory, using the Eiffel Tower as an antenna, exchanged sustained wireless (radio) signals with the United States Naval Observatory, using an antenna in Arlington, Virginia to determine the exact difference of longitude between the two institutions.[17]

NOFS panorama sm
Naval Observatory Flagstaff Station in Operation

In 1934, the last (then) large telescope to be installed at USNO saw "first light". This 40-inch aperture instrument[18] 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 the spaceborne Hubble Space Telescope. Unfortunately, light pollution forced USNO to think of other more viable locations to continue work, and so began a search. The final dark sky site chosen was Flagstaff, Arizona, and so the 40-inch telescope was moved to that location, beginning operations at the new Navy command, now called the Naval Observatory Flagstaff Station (NOFS). Those operations commenced in 1955,[19] and within a decade, the Navy's largest telescope, the 61-inch "Kaj Strand Astrometric Reflector" was built, seeing light at NOFS in 1964.[20]

The United States Naval Observatory 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, 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)[21] in the Astronomical Almanac, The Nautical Almanac, and on-line.[22]

Perhaps it is best known to the general public for its highly accurate ensemble of atomic clocks and its year 2000 time ball replacement.[23] The site also houses the largest astronomy library in the United States (and the largest astrophysical periodicals collection in the world).[24] The library includes a large collection of rare, often famous, physics and astronomy books from across the past millennium.

USNO continues to maintain its dark-sky observatory, NOFS, near Flagstaff, Arizona, which also now oversees the Navy Precision Optical Interferometer.[25] The Alternate Master Clock, mentioned above, also continues to operate at Schriever Air Force Base in Colorado.


In 1990, the Orbital Mechanics Department and Astronomical Applications Department were established, and Nautical Almanac Office became a division of the Astronomical Applications Department.[13][26] The Orbital Mechanics Department operated under P. K. Seidelmann until 1994 when the department was abolished, and its functions were moved to a group within the Astronomical Applications Department.[13] In 2010, USNO's astronomical 'department' known as the Naval Observatory Flagstaff Station (NOFS) was officially made autonomous as an Echelon Five command separate from USNO, but reporting to it. 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.

Official residence of the Vice President of the United States

Number One Observatory Circle, official home of the Vice President of the United States

Since 1974, a house situated in the grounds of the observatory, at Number One Observatory Circle, has been the official residence of the Vice President of the United States. The house is separated from the Naval Observatory, and was formerly the residence of its superintendent, and later the home of the Chief of Naval Operations.[27] The Observatory is therefore subject to tight security control enforced by the Secret Service.

According to a 15 May 2009 blog posting by Newsweek's Eleanor Clift,[28] Vice President Joe Biden revealed the existence of what Clift described as a bunker-like room in the residence. The bunker is the secure, undisclosed location where former Vice President Dick Cheney remained under protection in secret after the September 11 attacks: according to Clift's report, titled "Shining Light on Cheney's Hideaway":

Biden said a young naval officer giving him a tour of the residence showed him the hideaway, which is behind a massive steel door secured by an elaborate lock with a narrow connecting hallway lined with shelves filled with communications equipment.

Biden's press office subsequently issued a statement denying the bunker report, suggesting that Biden had instead been describing "an upstairs workspace".[29]

Time service

Atomic clock ensemble at the U.S. Naval Observatory

The U.S. Naval Observatory operates two Master Clock facilities. The primary facility, in Washington, D.C. maintains 57 HP/Agilent/Symmetricom 5071A-001 high performance cesium atomic clocks and 24 hydrogen masers. The alternate master clock, at Schriever Air Force Base, maintains 12 cesium clocks and 3 masers.[30] The observatory also operates four[31] rubidium atomic fountain clocks, which have a stability reaching 7×1016.[32] The observatory intends to build several more of this type for use at its two facilities.[30] The clocks used for the USNO timescale are kept in 19 environmental chambers, whose temperatures are kept constant to within 0.1 degree C and whose relative humidities (for all masers and most cesiums) are kept constant to within 1%. The timescale is based only upon the Washington DC clocks. On June 7, 2007, 70 standards were weighted in the timescale computations.[30]

The U.S. Naval Observatory provides public time service via 26[30] NTP servers on the public Internet,[33] and via telephone voice announcements:[34]

  • +1 202 762-1401 (Washington, D.C.)
  • +1 202 762-1069
  • +1 719 567-6742 (Colorado Springs)

The voice of actor Fred Covington (1928–1993) has been announcing the USNO time since 1978.[35]

The voice announcements follow the same pattern at both sites. They 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 five seconds after the local time.[36] 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,[37] and provides time to the Global Positioning System.

Instrument shop

The United States Naval Observatory Instrument shop has been manufacturing precise instrumentation since the early 1900s.[38]


  • 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 (USNOM) (v. 1–22: 1862–1880)
  • Observations made at the U.S. Naval Observatory (USNOO) (v. 1–7: 1887–1893)
  • Publications of the U.S. Naval Observatory, Second Series (PUSNO) (v. 1–16: 1900–1949)
  • U.S. Naval Observatory Circulars[39]
  • The Astronomical Almanac
  • The Nautical Almanac
  • The Air Almanac
  • Astronomical Phenomena

See also


  1. ^ Naval Meteorology and Oceanography Command. "The USNO's Mission — Naval Oceanography Portal". Usno.navy.mil. Retrieved 2011-07-27.
  2. ^ "National Executive Committee for Space-Based Positioning, Navigation, and Timing". Pnt.gov. 2011-06-17. Retrieved 2011-07-27.
  3. ^ "USNO Master Clock — Naval Oceanography Portal". Usno.navy.mil. Retrieved 2011-07-27.
  4. ^ Dick, S. J.; Dick, Steven J. (2003). Sky and Ocean Joined: The U. S. Naval Observatory 1830-2000 – Steven J. Dick – Google Books. ISBN 9780521815994. Retrieved 2013-08-04.
  5. ^ Frances Leigh Williams (1963). "VIII. Scientific Opportunity at Last". Matthew Fontaine Maury: Scientist of the Sea. Rutgers University Press, New Brunswick. p. 164. These different names for the Observatory and the term 'Hydrographic Office' were used interchangeably until December, 1854, when the Secretary of the Navy officially ruled that the proper designation was 'The United States Naval Observatory and Hydrographical office.'
  6. ^ Dick, S. J. (1991). "1991JHA 22...31D". Journal for the History of Astronomy. 22: 45–53. Bibcode:1991JHA....22...31D. doi:10.1177/002182869102200106. Retrieved 2013-08-04.
  7. ^ Portolano, M (2013-03-25). "John Quincy Adams's rhetorical crusade for astronomy" (PDF). Isis. 91 (3): 480–503. doi:10.1086/384852. PMID 11143785.
  8. ^ Matchette, R. B.; et al. (1995). Guide to Federal Records in the National Archives of the United States. Washington, DC: National Archives and Records Administration.
  9. ^ "The James Melville Gilliss Library".
  10. ^ "The Naval Observatory". The Baltimore Sun. December 14, 1842. p. 1.
  11. ^ "The new U.S. Naval Observatory, Washington". Monthly Notices of the Royal Astronomical Society. 54 (4): 261. 1894. Bibcode:1894MNRAS..54..261.. doi:10.1093/mnras/54.4.240.
  12. ^ "Weekly list of actions, 12/20/2016 through 1/13/2017". National Park Service. Retrieved 2017-01-26.
  13. ^ a b c Steven J. Dick (2003). Sky and ocean joined: the U.S. Naval Observatory, 1830–2000. Cambridge University Press. pp. 547–8, 574. ISBN 978-0-521-81599-4.
  14. ^ Dick, Steven J. (2004) The American Transit of Venus Expeditions of 1874 and 1882, Proceedings of the International Astronomical Union, International Astronomical Union, 2004, pp. 100–110, doi:10.1017/S1743921305001304. Published online May 23, 2005, retrieved February 2, 2012.
  15. ^ "Telescope: Naval Observatory 26-inch Refractor".
  16. ^ "The 26-inch "Great Equatorial" Refractor".
  17. ^ "Paris Time By Wireless," New York Times, November 22, 1913, pg 1.
  18. ^ "U.S. Naval Observatory Flagstaff – 1.0-m Ritchey-Chretien Reflector". Nofs.navy.mil. 1998-01-25. Retrieved 2011-07-27.
  19. ^ "USNO Flagstaff Station – History". Nofs.navy.mil. Retrieved 2011-07-27.
  20. ^ "U.S. Naval Observatory Flagstaff – 1.55-m Astrometric Reflector". Nofs.navy.mil. 2001-05-24. Retrieved 2011-07-27.
  21. ^ Naval Meteorology and Oceanography Command. "Catalog Information — Naval Oceanography Portal". Usno.navy.mil. Retrieved 2011-07-27.
  22. ^ Naval Meteorology and Oceanography Command. "Interactive Catalog and Image Search — Naval Oceanography Portal". Usno.navy.mil. Retrieved 2011-07-27.
  23. ^ Nemiroff, R.; Bonnell, J., eds. (1999-10-29). "The USNO Millennium Time Ball". Astronomy Picture of the Day. NASA. Retrieved 2015-12-27.
  24. ^ Naval Meteorology and Oceanography Command. "The James Melville Gilliss Library — Naval Oceanography Portal". Usno.navy.mil. Retrieved 2011-07-27.
  25. ^ "NPOI". Lowell Observatory.
  26. ^ Seidelmann, P. K. (1997). "Nautical Almanac Office 1975–1996". American Astronomical Society Meeting Abstracts. 191: 01.05. Bibcode:1997AAS...191.0105S. Retrieved 2011-07-27.
  27. ^ The Vice-President's Residence and Office Archived 2011-07-09 at the Wayback Machine accessdate=2013-02-27
  28. ^ Daniel Stone (2009-05-16). "Shining Light On Cheney's Hideaway". Blog.newsweek.com. Archived from the original on 2010-01-06. Retrieved 2011-07-27.
  29. ^ "Biden Reveals Location of Secret VP Bunker". FOX News. 2009-05-17. Archived from the original on 2009-05-19. Retrieved 2009-05-17.
  30. ^ a b c d Matsakis, Demetrios (2010-09-20), "Report from the U.S. Naval Observatory" (PDF), Civil GPS Service Interface Committee, retrieved 2010-10-31
  31. ^ http://www.usno.navy.mil/USNO/tours-events/u.s.-naval-observatory-declares-full-operational-capability-for-rubidium-fountain-clocks
  32. ^ "Initial Evaluation of the USNO Rubidium Fountain (PDF)" (PDF). Archived from the original (PDF) on 2011-06-15. Retrieved 2010-11-17.
  33. ^ "Usno Network Time Servers". Tycho.usno.navy.mil. Retrieved 2011-07-27.
  34. ^ "Telephone Time — Naval Oceanography Portal". Usno.navy.mil. Retrieved 2011-07-27.
  35. ^ "Keeping Time By Rubidium At The Naval Observatory". NPR. Retrieved 2015-03-11.
  36. ^ Telephone Time
  37. ^ "USNO Master Clock via Modem". Tycho.usno.navy.mil. Retrieved 2011-07-27.
  38. ^ Fey, Alan L. "The USNO Instrument Shop". ad.usno.navy.mil. Retrieved 2018-11-08.
  39. ^ Naval Meteorology and Oceanography Command. "U.S. Naval Observatory Special Publications — Naval Oceanography Portal". Usno.navy.mil. Retrieved 2011-07-27.

Further reading

  • Sky and Ocean Joined — The U.S. Naval Observatory 1830–2000 by Steven J. Dick (2003) ISBN 0-521-81599-1
  • Alden, Henry Mills; Wells, Thomas Bucklin; Hartman, Lee Foster; Allen, Frederick Lewis (1874). "The United States Naval Observatory". Harper's Magazine. 48: 531–539.

External links

Coordinates: 38°55′17″N 77°04′01″W / 38.921473°N 77.066946°W

Alvan Clark

Alvan Clark (March 8, 1804 – August 19, 1887), born in Ashfield, Massachusetts, the descendant of a Cape Cod whaling family of English ancestry, was an American astronomer and telescope maker. He was a portrait painter and engraver (c.1830s-1850s), and at the age of 40 became involved in telescope making. Using glass blanks made by Chance Brothers of Birmingham and Feil-Mantois of Paris, his firm Alvan Clark & Sons ground lenses for refracting telescopes, including the largest in the world at the time: the 18.5-inch (47 cm) at Dearborn Observatory at the Old University of Chicago (the lens was originally intended for Ole Miss), the two 26-inch (66 cm) telescopes at the United States Naval Observatory and McCormick Observatory, the 30-inch (76 cm) at Pulkovo Observatory (destroyed in the Siege of Leningrad; only the lens survives), the 36-inch (91 cm) telescope at Lick Observatory (still third-largest) and later the 40-inch (100 cm) at Yerkes Observatory, which remains the largest successful refracting telescope in the world. One of Clark's sons, Alvan Graham Clark, discovered the dim companion of Sirius. His other son was George Bassett Clark; both sons were partners in the firm.

Two craters bear his name. The crater Clark on the Moon is jointly named for him and his son, Alvan Graham Clark, and one on Mars is named in his honor.Clark was also competitive in target shooting and received a patent for his device to allow bullets to be seated into a muzzle loading rifle without damage to either the bullet or the rifle's muzzle. Exclusive license to this patent (1,565 of April 24, 1840) was made to Edwin Wesson, brother of Daniel B. Wesson.

American Ephemeris and Nautical Almanac

The American Ephemeris and Nautical Almanac was published for the years 1855 to 1980, containing information necessary for astronomers, surveyors, and navigators. It was based on the original British publication, The Nautical Almanac and Astronomical Ephemeris, with which it merged to form The Astronomical Almanac, published from the year 1981 to the present.

Astronomical Almanac

The Astronomical Almanac is an almanac published by the United States Naval Observatory (USNO) and Her Majesty's Nautical Almanac Office (HMNAO); it also includes data supplied by many scientists from around the world. It is considered a worldwide resource for fundamental astronomical data, often being the first publication to incorporate new International Astronomical Union resolutions. The almanac largely contains solar system ephemeris and catalogs of selected stellar and extragalactic objects. The material appears in sections, each section addressing a specific astronomical category. The book also includes references to the material, explanations, and examples. It is available one year in advance of its date.

The Astronomical Almanac Online is a companion to the printed volume. It is designed to broaden the scope of the publication, not duplicate the data. In addition to ancillary information, the Astronomical Almanac Online extends the printed version by providing data best presented in machine-readable form.

The Explanatory Supplement to the Astronomical Almanac, currently in its third edition (2013), provides detailed discussion of usage and data reduction methods used by the Almanac. It covers its history, significance, sources, methods of computation, and use of the data. Because the Astronomical Almanac prints primarily positional data, this book goes into great detail on techniques to get astronomical positions. Earlier editions of the supplement were published in 1961 and in 1992.

Charon (moon)

Charon, also known as (134340) Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It has a mean radius of 606 km. It was discovered in 1978 at the United States Naval Observatory in Washington, D.C., using photographic plates taken at the United States Naval Observatory Flagstaff Station (NOFS).

With half the diameter and one eighth the mass of Pluto, Charon is a very large moon in comparison to its parent body. Its gravitational influence is such that the barycenter of the Plutonian system lies outside Pluto.

The reddish-brown cap of the north pole of Charon is composed of tholins; organic macromolecules that may be essential ingredients of life. These tholins were produced from methane, nitrogen and related gases released from the atmosphere of Pluto and transferred over 19,000 km (12,000 mi) to the orbiting moon.The New Horizons spacecraft is the only probe that has visited the Pluto system. It approached Charon to within 27,000 km (17,000 mi) in 2015.

Civil time

In modern usage, civil time refers to statutory time scales designated by civilian authorities, or to local time indicated by clocks. Modern civil time is generally standard time in a time zone at a fixed offset from Coordinated Universal Time (UTC) or from Greenwich Mean Time (GMT), possibly adjusted by daylight saving time during part of the year. UTC is calculated by reference to atomic clocks, and was adopted in 1972. Older systems use telescope observations.

In traditional astronomical usage, civil time was mean solar time reckoned from midnight. Before 1925, the astronomical time 00:00:00 meant noon, twelve hours after the civil time 00:00:00 which meant midnight. HM Nautical Almanac Office in the United Kingdom used Greenwich Mean Time (GMT) for both conventions, leading to ambiguity, whereas the Nautical Almanac Office at the United States Naval Observatory used GMT for the pre-1925 convention and Greenwich Civil Time (GCT) for the post-1924 convention until 1952. In 1928, the International Astronomical Union introduced the term Universal Time for GMT beginning at midnight, but the two Nautical Almanac Offices did not accept it until 1952.

Dennis McCarthy (scientist)

Dennis D. McCarthy is a former Director of Time at the United States Naval Observatory. McCarthy also works for the International Earth Rotation and Reference Systems Service.

Edwin Taylor Pollock

Edwin Taylor Pollock (October 25, 1870 – June 4, 1943) was a career officer in the United States Navy, serving in the Spanish–American War and in World War I. He was later promoted to the rank of captain. Like many naval officers, his name was often abbreviated using initials: E. T. Pollock.

As a young ensign, Pollock served aboard USS New York during the Spanish–American War. After the war, he rose through the ranks, served on several ships, and did important research into wireless communication. In 1917, less than a week before the United States entered World War I, he won a race against a fellow officer to receive the U.S. Virgin Islands from Denmark, and served as the territory's first acting governor. During the war, he was promoted to captain and a vessel under his command transported 60,000 American soldiers to France, for which he was awarded a Navy Cross. Afterward, he was made the eighth Naval Governor of American Samoa and then the superintendent of the United States Naval Observatory, before retiring in 1927.

Embassy of Iraq in Washington, D.C.

The Embassy of Iraq in Washington, D.C. is the diplomatic mission of the Republic of Iraq to the United States. The embassy is located at 3421 Massachusetts Avenue, Northwest, in the Embassy Row neighborhood, near the United States Naval Observatory.

The consular section of the embassy is located in the former chancery at 1801 P Street, N.W., near Dupont Circle. The embassy also operates a commercial attaché at 1155 15th Street, NW, a cultural attaché at 1638 R Street, NW, and a military attaché at 2600 Virginia Avenue, NW.

Full-sky Astrometric Mapping Explorer

Full-sky Astrometric Mapping Explorer (or FAME) was a proposed astrometric satellite designed to determine with unprecedented accuracy the positions, distances, and motions of 40 million stars within our galactic neighborhood (distances by stellar parallax possible). This database was to allow astronomers to accurately determine the distance to all of the stars on this side of the Milky Way galaxy, detect large planets and planetary systems around stars within 1,000 light years of the Sun, and measure the amount of dark matter in the galaxy from its influence on stellar motions. It was to be a collaborative effort between the United States Naval Observatory (USNO) and several other institutions. FAME would have measured stellar positions to less than 50 microarcseconds. The NASA MIDEX mission was scheduled for launch in 2004. In January 2002, however, NASA abruptly cancelled this mission, mainly due to concerns about its price tag which grew from $160 million to $220 million.

This would have been an improvement over the High Precision Parallax Collecting Satellite (Hipparcos) which operated 1989-1993 and produced various star catalogs. Astrometric parallax measurements form part of the cosmic distance ladder, and can also be measured by other Space telescopes such as Hubble (HST) or ground-based telescopes to varying degrees of precision.

Compared to the FAME accuracy of 50 microarcseconds, the Gaia mission is planning 10 microarcseconds accuracy, for mapping stellar parallax up to a distance of tens of thousands of light-years from Earth.

Glover Park

Glover Park is a neighborhood in northwest Washington, D.C., about a half mile north of Georgetown and just west of the United States Naval Observatory and Number One Observatory Circle (the Vice President's mansion). Every morning and evening, Glover Park residents can hear the Naval Observatory play the sounding of colors synchronized to the nation's Master Clock. It is named after Charles Carroll Glover.

Index Catalogue of Visual Double Stars

The Index Catalogue of Visual Double Stars, or IDS, is a catalog of double stars. It was published by Lick Observatory in 1963 and contains measurements for 64,250 objects, covering the entire sky. The database used to construct this catalog was later transferred from Lick Observatory to the United States Naval Observatory, where it became the basis for the Washington Double Star Catalog.

Naval Observatory Vector Astrometry Subroutines

The Naval Observatory Vector Astrometry Software (NOVAS) is a software library for astrometry-related numerical computations. It is developed by the Astronomical Applications Department, United States Naval Observatory. Currently, NOVAS has three different editions for C, Fortran, and Python, respectively.

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) and Lowell Observatory. The NPOI primarily produces space imagery and astrometry, the latter a major component required for the safe position and navigation of all manner of vehicles for the DoD. The facility is located at Lowell's Anderson Mesa Station on Anderson Mesa about 25 kilometers (16 mi) southeast of Flagstaff, Arizona (US). Until November 2011, the facility was known as the Navy Prototype Optical Interferometer (NPOI). Subsequently, the instrument was temporarily renamed the Navy Optical Interferometer, and now permanently, the Kenneth J. Johnston Navy Precision Optical Interferometer (NPOI) – reflecting both the operational maturity of the facility, and paying tribute to its principal driver and retired founder, Kenneth J. Johnston.The NPOI project was initiated by the United States Naval Observatory (USNO) in 1987. Lowell joined the project the following year when the USNO decided to build the NPOI at Anderson Mesa. The first phase of construction was completed in 1994, which allowed the interferometer to see its first fringes, or light combined from multiple sources, that year. The Navy began regular science operations in 1997. The NPOI has been continuously upgraded and expanded since then, and has been operational for a decade. The workings of NPOI as a classic interferometer, are described at Scholarpedia, and at the NPOI site.

Richard E. Keating

Richard E. Keating (29 May 1941 – 5 Oct 2006) is an astronomer best known for the Hafele–Keating experiment, a test of Einstein's theory of relativity performed while he was working at the United States Naval Observatory.

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 almanac to contain data dedicated to the convenient determination of longitude at sea. It was originally published from the Royal Greenwich Observatory in England. A detailed account of how the publication was produced in its earliest years has been published by the National Maritime Museum.Since 1958 (with the issue for the year 1960), Her Majesty's Nautical Almanac Office and the US Naval Observatory have jointly published a unified Nautical Almanac, for use by the navies of both countries.

United States Naval Observatory Flagstaff Station

The United States Naval Observatory Flagstaff Station (NOFS), is an astronomical observatory near Flagstaff, Arizona, USA. It is the national dark-sky observing facility under the United States Naval Observatory (USNO). NOFS and USNO combine as the Celestial Reference Frame manager for the U.S. Secretary of Defense.

Washington Double Star Catalog

The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for (as of June 2017) 141,743 pairs of double stars. The catalog also includes multiple stars. In general, a multiple star with n components will be represented by entries in the catalog for n-1 pairs of stars.

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