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The Royal Observatory, Greenwich (ROG; known as the Old Royal Observatory from 1957 to 1998, when the working Royal Greenwich Observatory, RGO, temporarily moved south from Greenwich to
Herstmonceux Herstmonceux ( , ) is a village and civil parish In England, a civil parish is a type of administrative parish used for local government. It is a territorial designation which is the lowest tier of local government below districts and c ...
) is an
observatory An observatory is a location used for observing terrestrial, marine, or celestial events. Astronomy, climatology/meteorology, geophysics, geophysical, oceanography and volcanology are examples of disciplines for which observatories have been cons ...

observatory
situated on a hill in
Greenwich Park Greenwich Park is a former hunting Hunting is the practice of seeking, pursuing and capturing or killing wildlife or feral animals. The most common reasons for humans to hunt are to harvest useful animal products (meat, fur/hide (skin), hide, ...
in south east London, overlooking the
River Thames The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, se ...
to the north. It played a major role in the history of
astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses mathematics, phys ...
and
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, ...

navigation
, and because the
Prime Meridian #REDIRECT Prime meridian#REDIRECT Prime meridian A prime meridian is the meridian (geography), meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meri ...
passes through it, it gave its name to
Greenwich Mean Time Greenwich Mean Time (GMT) is the Local mean time, mean solar time at the Royal Observatory, Greenwich, Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, i ...
, the precursor to today's
Coordinated Universal Time Coordinated Universal Time or UTC is the primary time standard A time standard is a specification for measuring time: either the rate at which time passes; or points in time; or both. In modern times, several time specifications have been o ...
(UTC). The ROG has the
IAU The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a Non-governmental organization, nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting ...

IAU
observatory code of 000, the first in the list. ROG, the
National Maritime Museum The National Maritime Museum (NMM) is a maritime museum in Greenwich, London. It is part of Royal Museums Greenwich, a network of museums in the Maritime Greenwich World Heritage Site. Like other publicly funded national museums in the United ...

National Maritime Museum
, the
Queen's House Queen's House is a former royal residence built between 1616 and 1635 in Greenwich Greenwich ( , , , or ) is a town in South London, south-east London, England, centred east-southeast of Charing Cross and located in the Historic county of ...
and the
clipper ship A clipper was a type of mid-19th-century Merchant ship, merchant Sailing ship, sailing vessel, designed for speed. Clippers were generally narrow for their length, small by later 19th century standards, could carry limited bulk freight, and had ...
''
Cutty Sark ''Cutty Sark'' is a British clipper A clipper was a type of mid-19th-century merchant sailing vessel, designed for speed. Clippers were generally narrow for their length, small by later 19th century standards, could carry limited bulk fre ...

Cutty Sark
'' are collectively designated
Royal Museums Greenwich Royal Museums Greenwich is an organisation comprising four museums in Greenwich Greenwich ( , , , or ) is a town in South London, south-east London, England, centred east-southeast of Charing Cross and located in the Historic county of Engla ...
. The observatory was commissioned in 1675 by , with the
foundation stone The cornerstone (or foundation stone or setting stone) is the first stone set in the construction of a masonry Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''mason ...

foundation stone
being laid on 10 August. The site was chosen by
Sir Christopher Wren Sir Christopher Wren President of the Royal Society, PRS Fellow of the Royal Society, FRS (; – ) was one of the most highly acclaimed English architects in history, as well as an anatomist, astronomer, geometer, and mathematician-physicist. H ...
, a former
Savilian Professor of Astronomy The position of Savilian Professor of Astronomy was established at the University of Oxford in 1619. It was founded (at the same time as the Savilian Professor of Geometry, Savilian Professorship of Geometry) by Henry Savile (Bible translator), Sir ...
; as
Greenwich Park Greenwich Park is a former hunting Hunting is the practice of seeking, pursuing and capturing or killing wildlife or feral animals. The most common reasons for humans to hunt are to harvest useful animal products (meat, fur/hide (skin), hide, ...
was a royal estate, no new land needed to be bought. At that time the king also created the position of
Astronomer Royal Astronomer Royal is a senior post in the Royal Households of the United Kingdom. There are two officers, the senior being the Astronomer Royal dating from 22 June 1675; the second is the Astronomer Royal for Scotland dating from 1834. The post ...
, to serve as the director of the observatory and to "apply himself with the most exact care and diligence to the rectifying of the tables of the motions of the heavens, and the places of the fixed stars, so as to find out the so much desired longitude of places for the perfecting of the art of navigation." He appointed
John Flamsteed John Flamsteed FRS (19 August 1646 – 31 December 1719) was an English astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astr ...

John Flamsteed
as the first Astronomer Royal. The building was completed in the summer of 1676. The building was often called "Flamsteed House", in reference to its first occupant. The scientific work of the observatory was relocated elsewhere in stages in the first half of the 20th century, and the Greenwich site is now maintained almost exclusively as a museum, although the AMAT telescope became operational for astronomical research in 2018.


History


Chronology

*1675 – 22 June, Royal Observatory founded by . *1675 – 10 August, construction began. *1714
Longitude Act The Longitude Act 1714 was an Act of Parliament Acts of parliament, sometimes referred to as primary legislation, are texts of law passed by the Legislature, legislative body of a jurisdiction (often a parliament or council). In most countries, act ...

Longitude Act
established the
Board of Longitude The Commissioners for the Discovery of the Longitude at Sea, or more popularly Board of Longitude, was a British government body formed in 1714 to administer a scheme of prizes intended to encourage innovators to solve the problem of finding longit ...
and
Longitude rewards The longitude rewards were the system of inducement prizes offered by the British government for a simple and practical method for the precise determination of a ship's longitude Longitude (, ), is a geographic coordinate that specifies th ...
. The Astronomer Royal was, until the Board was dissolved in 1828, always an ex officio Commissioner of Longitude. *1767 The fifth Astronomer Royal
Nevil Maskelyne The Rev Dr Nevil Maskelyne DD FRS FRSE (; 6 October 1732 – 9 February 1811) was the fifth British Astronomer Royal. He held the office from 1765 to 1811. He was the first person to scientifically measure the mass of the planet Earth. Bio ...

Nevil Maskelyne
began publication of ''
The Nautical Almanac ''The Nautical Almanac'' has been the familiar name for a series of official British almanacs An almanac (also spelled ''almanack'' and ''almanach'') is an annual publicationAnnual publications, more often simply called annuals, are periodical p ...
'', based on observations made at the Observatory. *1818 Oversight of the Royal Observatory was transferred from the
Board of Ordnance The Board of Ordnance was a British government The Government of the United Kingdom, domestically referred to as Her Majesty's Government, is the central government of the United Kingdom of Great Britain and Northern Ireland.marine chronometer Marine is an adjective meaning of or pertaining to the sea or ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
s. *1833 Daily time signals began, marked by dropping a
time ball A time ball or timeball is an obsolete 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 mari ...
. *1838 – Sheepshanks equatorial, a 6.7 inch (170 mm) aperture
refracting telescope 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 de ...
installed. *1893 – The 28-inch Great refractor installed. *1899 The New Physical Observatory (now known as the South Building) was completed. *1924 Hourly time signals (
Greenwich Time Signal The Greenwich Time Signal (GTS), popularly known as the pips, is a series of six short tones broadcast at one-second intervals by many BBC Radio stations. The pips were introduced in 1924 and have been generated by the BBC since 1990 to mark the ...
) from the Royal Observatory were first broadcast on 5 February. *1931
Yapp telescope The Yapp telescope is a 36-inch (3 foot / ~91.44 cm) reflecting telescope of the United Kingdom, now located at the Observatory Science Centre at Herstmonceux Herstmonceux ( , ) is a village and civil parish In England, a civil parish is ...
ordered. *1948 Office of the Astronomer Royal was moved to
Herstmonceux Herstmonceux ( , ) is a village and civil parish In England, a civil parish is a type of administrative parish used for local government. It is a territorial designation which is the lowest tier of local government below districts and c ...
in
East Sussex East Sussex is a county A county is a geographical region of a country used for administrative or other purposesChambers Dictionary The ''Chambers Dictionary'' (''TCD'') was first published by William Chambers (publisher), William and R ...

East Sussex
. *1957 Royal Observatory completed its move to Herstmonceux, becoming the Royal Greenwich Observatory (RGO). The Greenwich site was renamed the Old Royal Observatory. *1990 RGO moved to
Cambridge Cambridge ( ) is a university city and the county town In the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' ...

Cambridge
. *1998 RGO closed. Greenwich site was returned to its original name, the Royal Observatory, Greenwich, and was made part of the
National Maritime Museum The National Maritime Museum (NMM) is a maritime museum in Greenwich, London. It is part of Royal Museums Greenwich, a network of museums in the Maritime Greenwich World Heritage Site. Like other publicly funded national museums in the United ...

National Maritime Museum
. *2011 The Greenwich museums, including the ROG, became collectively the Royal Museums Greenwich.


Site

There had been significant buildings on this land since the reign of William I.
Greenwich Palace Greenwich ( , , , or ) is a town in South London, south-east London, England, centred east-southeast of Charing Cross and located in the Historic county of England, historic county of Kent. For administrative purposes it formed part of the M ...
, on the site of the present-day Maritime Museum, was the birthplace of both
Henry VIII Henry VIII (28 June 149128 January 1547) was King of England This list of kings and queens of the Kingdom of England The Kingdom of England was a sovereign state on the island of Great Britain from 12 July 927, when it emerged fro ...

Henry VIII
and his daughters
Mary I Mary I (18 February 1516 – 17 November 1558), also known as Mary Tudor, and as "Bloody Mary" by her Protestant Protestantism is a form of that originated with the 16th-century , a movement against what its followers perceived to ...

Mary I
and
Elizabeth I Elizabeth I (7 September 153324 March 1603) was Queen of England and Ireland Ireland ( ; ga, Éire ; Ulster-Scots: ) is an island upright=1.15, Great_Britain.html"_;"title="Ireland_(left)_and_Great_Britain">Ireland_(left)_an ...

Elizabeth I
;
the Tudors ''The Tudors'' is a historical fiction television series set primarily in 16th-century England, created and written by Michael Hirst and produced for the American premium cable television channel Showtime Showtime or Show Time may refer to: ...
used Greenwich Castle, which stood on the hilltop that the Observatory presently occupies, as a hunting lodge. Greenwich Castle was reportedly a favourite place for Henry VIII to house his mistresses, so that he could easily travel from the Palace to see them. In 1676 the main building of the observatory, now known as Flamsteed House, was completed on Greenwich hill.


Establishment

The establishment of a Royal Observatory was proposed in 1674 by Sir
Jonas Moore Sir Jonas Moore, Fellow of the Royal Society, FRS (1617–1679) was an English mathematician, Cadastral, surveyor, ordnance officer, and patron of astronomy. He took part in two of the most ambitious English civil engineering projects of the 17th ...
who, in his role as
Surveyor-General of the Ordnance The Surveyor-General of the Ordnance was a subordinate of the Master-General of the Ordnance and a member of the Board of Ordnance, a British government body, from its constitution in 1597. Appointments to the post were made by the crown under Lett ...
, persuaded King Charles II to create the observatory, with John Flamsteed installed as its director. The Ordnance Office was given responsibility for building the Observatory, with Moore providing the key instruments and equipment for the observatory at his own personal cost. Flamsteed House, the original part of the Observatory, was designed by Sir
Christopher Wren Sir Christopher Wren PRS FRS FRS may also refer to: Government and politics * Facility Registry System, a centrally managed Environmental Protection Agency database that identifies places of environmental interest in the United States * Fa ...

Christopher Wren
, probably assisted by
Robert Hooke Robert Hooke FRS FRS may also refer to: Government and politics * Facility Registry System, a centrally managed Environmental Protection Agency database that identifies places of environmental interest in the United States * Family Resources ...
, and was the first purpose-built scientific research facility in Britain. It was built for a cost of £520 (£20 over budget; ) out of largely recycled materials on the foundations of Duke Humphrey's Tower, the forerunner of Greenwich Castle, which resulted in the alignment being 13 degrees away from true North, somewhat to Flamsteed's chagrin. Moore donated two clocks, built by
Thomas Tompion Thomas Tompion (1639–1713) was an English clockmaker, watchmaker and mechanician who is still regarded to this day as the "Father of English Clockmaking". Tompion's work includes some of the most historic and important clocks and watches in t ...
, which were installed in the 20 foot high Octagon Room, the principal room of the building. They were of unusual design, each with a pendulum 13 feet (3.96 metres) in length mounted above the clock face, giving a period of four seconds and an accuracy, then unparalleled, of seven seconds per day. The original observatory housed the astronomer royal, his assistant and his family as well as the scientific instruments to be used by Flamsteed in his work on stellar tables. Over time the institution became a more established institution, thanks to its links to long-lasting government boards (the
Board of Ordnance The Board of Ordnance was a British government The Government of the United Kingdom, domestically referred to as Her Majesty's Government, is the central government of the United Kingdom of Great Britain and Northern Ireland.Board of Longitude The Commissioners for the Discovery of the Longitude at Sea, or more popularly Board of Longitude, was a British government body formed in 1714 to administer a scheme of prizes intended to encourage innovators to solve the problem of finding longit ...
) and oversight by a Board of Visitors, founded in 1710 and made up of the President and Members of the council of the Royal Society. By the later 18th century it incorporated additional responsibilities such as publishing 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 each ...
'', advising government on technical matters, disseminating time, making meteorological and magnetic observations and undertaking astrophotography and spectroscopy. The physical site and the numbers of staff increased over time as a result.


Positional astronomy and star charts

When the observatory was founded in 1675, one of the best star catalogues was
Tycho Brahe Tycho Brahe ( ; born Tyge Ottesen Brahe; 14 December 154624 October 1601) was a Danish astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. T ...

Tycho Brahe
's 1000-star catalogue from 1598. However, this catalogue was not accurate enough to determine longitudes. One of Flamsteed's first orders of business was creating more accurate charts suitable for this purpose. One of the noted charts made at Greenwich was by the Astronomer Royal
James Bradley James Bradley (1692–1762) was an English astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as star ...

James Bradley
, who between 1750 and 1762 charted sixty thousand stars, so accurately his catalogues were used even in the 1940s. Bradley was the third
Astronomer Royal Astronomer Royal is a senior post in the Royal Households of the United Kingdom. There are two officers, the senior being the Astronomer Royal dating from 22 June 1675; the second is the Astronomer Royal for Scotland dating from 1834. The post ...
, and his tenure started in 1742. In the early 19th century, the main positional devices were the Troughton Transit instrument and a mural circle, but after
George Biddell Airy Sir George Biddell Airy (; 27 July 18012 January 1892) was an English mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics a ...

George Biddell Airy
took over as Astronomer Royal in 1835, he embarked on a plan to have better instruments at Greenwich observatory.
Positional astronomy Spherical astronomy, or positional astronomy, is a branch of observational astronomy Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also ...

Positional astronomy
was one of the primary functions of Greenwich for the Admiralty. The Astronomer Royal Airy was an advocate of this and the transit circle instrument he had installed in 1851 was used for a century for positional astronomy. One of the difficulties with positional astronomy, is accounting for the . Sources of error include the precision of the instrumentation, and then there has to be accounting for
precession Precession is a change in the orientation Orientation may refer to: Positioning in physical space * Map orientation, the relationship between directions on a map and compass directions * Orientation (housing), the position of a building with re ...

precession
,
nutation Nutation (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman ...
, and aberration. Sources of error in the instrument have to be tracked down and accounted for to produced more accurate results. The transit circle makes two measurements; along with a clock, the time a star passed a certain point in the sky as the Earth rotates, and the vertical angle of the location of the star. The instrument can be used to plot the locations of stars, or alternately, with an accurate star chart, the time at the location of the instrument.


1832 Transit of Mercury

The
Shuckburgh telescope The Shuckburgh telescope or Shuckburgh equatorial refracting telescope was a diameter aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system ...
of the Royal Observatory in London was used for the 1832
transit of Mercury A transit of Mercury across the Sun takes place when the planet Mercury (planet), Mercury passes directly (Transit (astronomy), transits) between the Sun and a superior planet, becoming visible against (and hence obscuring a small portion of) t ...
. It was equipped with a
filar micrometer A filar micrometer is a specialized eyepiece used in astronomical telescopes for astrometry in the optical wavelength range to determine precise positions of stars. ''Courtesy NASA/JPL-Caltech'' Astrometry is the branch of astronomy Astro ...
by
Peter Dollond Peter Dollond (24 February 1731 – 2 July 1820) was an English maker of optical instruments, the son of John Dollond. He is known for his successful optics business, and for the invention of the apochromat. Biography Dollond was born in Kensingt ...

Peter Dollond
and was used to provide a report of the events as seen through the small refractor. By observing the transit in combination with timing it and taking measures, a diameter for the planet was taken. They also reported the peculiar effects that they compared to pressing a coin into the Sun. The observer remarked:


Greenwich Meridian

British astronomers have long used the Royal Observatory as a basis for measurement. Four separate meridians have passed through the buildings, defined by successive instruments. The basis of
longitude Longitude (, ) is a geographic coordinate A geographic coordinate system (GCS) is a coordinate system associated with position (geometry), positions on Earth (geographic position). A GCS can give positions: *as Geodetic coordinates, ...

longitude
, the meridian that passes through the
transit circle The meridian circle is an instrument for timing of the passage of stars across the local meridian (astronomy), meridian, an event known as a culmination, while at the same time measuring their angular distance from the nadir. These are special purp ...
, first used in 1851, was adopted as the world's
Prime Meridian #REDIRECT Prime meridian#REDIRECT Prime meridian A prime meridian is the meridian (geography), meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meri ...

Prime Meridian
at the
International Meridian Conference The International Meridian Conference was a conference held in October 1884 in Washington, D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Mem ...
at
Washington, D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument The Washington Monument is an obelisk within the National Mall The National Mall is a Landscape architecture, landscaped ...
on 22 October 1884 (voting took place on 13 October). Subsequently, nations across the world used it as their standard for mapping and timekeeping. The Prime Meridian was marked by a brass (later replaced by
stainless steel Stainless steel is a group of ferrous alloys that contain a minimum of approximately 11% chromium Chromium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistr ...
) strip in the Observatory's courtyard once the buildings became a museum in 1960, and, since 16 December 1999, has been marked by a powerful green
laser A laser is a device that emits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as h ...

laser
shining north across the London night sky. Since the first triangulation of Great Britain in the period 1783–1853,
Ordnance Survey , nativename_a = , nativename_r = , logo = Ordnance Survey 2015 Logo.svg , logo_width = 240px , logo_caption = , seal = , seal_width = , seal_caption = , picture = , picture_width = , picture_caption = , formed = , preceding1 = , di ...
maps have been based on an earlier version of the Greenwich meridian, defined by the transit instrument of
James Bradley James Bradley (1692–1762) was an English astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as star ...

James Bradley
. When the Airy circle (5.79 m to the east) became the reference for the meridian, the difference resulting from the change was considered small enough to be neglected. When a new triangulation was done between 1936 and 1962, scientists determined that in the Ordnance Survey system the longitude of the international Greenwich meridian was not 0° but 0°00'00.417" (about 8 m) East. Besides the change of the reference line, imperfections of the surveying system added another discrepancy to the definition of the origin, so that the Bradley line itself is now 0°00'00.12" East of the Ordnance Survey Zero Meridian (about 2.3m). This old astronomical prime meridian has been replaced by a more precise prime meridian. When Greenwich was an active observatory, geographical coordinates were referred to a local
oblate spheroid A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric In mathematics, a quadric or quadric surface (quadric hypersurface in higher dimension thumb , 236px , The first four spatial dimensions, repres ...
called a datum known as a geoid, whose surface closely matched local mean sea level. Several datums were in use around the world, all using different spheroids, because mean sea level undulates by as much as 100 metres worldwide. Modern geodetic reference systems, such as the
World Geodetic System The World Geodetic System (WGS) is a standard for use in cartography Cartography (; from χάρτης ''chartēs'', "papyrus, sheet of paper, map"; and γράφειν ''graphein'', "write") is the study and practice of making and using ...
and the
International Terrestrial Reference Frame The International Terrestrial Reference System (ITRS) describes procedures for creating reference frame In physics, a frame of reference (or reference frame) consists of an abstract coordinate system In geometry Geometry (from the grc ...
, use a single oblate spheroid, fixed to the Earth's gravitational centre. The shift from several local spheroids to one worldwide spheroid caused all geographical coordinates to shift by many metres, sometimes as much as several hundred metres. The Prime Meridian of these modern reference systems, called IERS (International Earth Rotation and Reference Systems Service) Reference Meridian (shortly called IRM), is 102.5 metres east of the Greenwich astronomical meridian represented by the stainless steel strip, which is now 5.31 
arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of Angular unit, angular measurement equal to of one Degree (angle), degree. Since one degree is of a turn (geometry), turn (or complete rotati ...
s West. The modern location of the Airy Transit is as the IRM is at 0 degree in longitude nowadays. International time from the end of the 19th century until
UT1 Universal Time (UT) is a time standard based on Earth's rotation. There are several versions of Universal Time, which differ by up to a few seconds. The most commonly used are Coordinated Universal Time Coordinated Universal Time or UTC is t ...
was based on
Simon Newcomb Simon Newcomb (March 12, 1835 – July 11, 1909) was a Canadians, Canadian–Americans, American astronomer, applied mathematician, and autodidactic polymath. He served as Professor of Mathematics in the United States Navy and at Johns Hopkins Un ...

Simon Newcomb
's equations, giving a mean sun about 0.18 seconds behind UT1 (the equivalent of 2.7 arcseconds) as of 2013; it coincided in 2013 with a meridian halfway between Airy's circle and the IERS origin: .


Greenwich Mean Time

Greenwich Mean Time (GMT) was until 1954 based on celestial observations made at Greenwich, and later on observations made at other observatories. GMT was formally renamed as
Universal Time#REDIRECT Universal Time Universal Time (UT) is a time standard based on Earth's rotation. There are several versions of Universal Time, which differ by up to a few seconds. The most commonly used are Coordinated Universal Time (UTC) and UT1 (see ...

Universal Time
in 1935, but is still commonly referred to as GMT, though they are not identical. It is now calculated from observations of extra-galactic radio sources. The observatory is noted as the home of the prime meridian and Greenwich mean time. A key instrument for determining time was the Airy Transit Circle, which was used primarily from 1851 to 1938. It was agreed in 1884 that the "meridian line marked by the cross-hairs in the Airy Transit Circle eyepiece would indicate 0° longitude and the start of the Universal Day" according to RMG. The time is determined by marking the time a star of known location would pass through the aimpoint of the telescope. In a reverse case, this type of instrument was also used for making star charts. The stars whose position was known precisely enough for being used for time determination, were called "clock stars."


Greenwich Time Ball

The red
time ball A time ball or timeball is an obsolete 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 mari ...
of Greenwich was established in 1833, and is noted as a public time signal.
/ref> The time ball in modern times is normally in a lowered position, then starting at 12:55pm, the ball begins to rise, then at 12:58 it reaches the top; at 1pm the ball drops. To help mariners at the port and others in line of sight of the observatory to synchronise their clocks to GMT, Astronomer Royal
John Pond John Pond FRS (1767 – 7 September 1836) was a renowned English astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomica ...

John Pond
installed a very visible time ball that drops precisely at 1pm (13:00) every day atop the observatory in 1833. Initially it was dropped by an operator; from 1852 it was released automatically via an electric impulse from the Shepherd Master Clock. The ball is still dropped daily at 13:00 (GMT in winter, BST in summer). The original time ball system was built by Messrs Maudslay and Field, and cost £180. The five-foot diameter ball was made of wood and leather. In the original ball system, it was hoisted by a rope up from the Octagon room, and there was catch at the top to hold it. This could then be triggered by hand, while observing the time on an astronomical month clock, that was regulated to the
mean solar time planet like the Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consisting of continent A continent is one of several large landmasses. ...
. By dropping the ball, the public, mariners, and clock makers could then get a time signal by viewing it from afar. The ball drop would be repeated at 2pm also if possible. The reason why 12 noon was not chosen was because astronomers at the observatory would record when the Sun crossed the meridian at that time on that day. In rare occasions where the ball could get stuck due to icing or snow, and if the wind was too high it would not be dropped. In 1852, it was established to distribute a time signal by the telegraph wires also. The time ball was extremely popular with the public, chronometers, railways, mariners, and there was a petition to have another time ball established in
Southampton Southampton () is a port A port is a maritime law, maritime facility comprising one or more Wharf, wharves or loading areas, where ships load and discharge Affreightment, cargo and passengers. Although usually situated on a sea ...
also.


1890s

The 1890s marked the addition of a new larger refractor, the 28-inch Grubb in the Great Equatorial Dome. Because the new telescope was longer than the old Great refractor, the new dome had to be bigger; thus the famous "onion dome" that expands beyond the diameter of the turret was established. For the tricentennial, it was revitalized with a fibre-glass dome; the old one made of
papier-mâché papier-mâché masks, Haiti Papier-mâché (, ; , literally "paper-mash") is a composite material consisting of paper pieces or pulp, sometimes reinforced with textiles, bound with an adhesive, such as glue, starch, or wallpaper adhesive, wallp ...
and iron had been taken down. The telescope was installed by 1893, with 28-inch diameter glass doublet lens made by Grubb from Chance of Birmingham glass. The new dome was made by T. Cooke and Sons. This replaced a smaller drum-shaped dome. The two-foot reflector was a famous metal-mirror telescope that had been used to discover the Moons
Triton Triton commonly refers to: * Triton (mythology), a Greek god * Triton (moon), a satellite of Neptune Triton may also refer to: Biology * Triton cockatoo, a parrot * Triton (gastropod), a group of sea snails * ''Triton'', a synonym of ''Triturus'', ...

Triton
and Hyperion. It was donated to the observatory in the 1880s, but was taken down in the 1890s. The 1890s also saw the construction of the Altazimuth Pavilion, completed in 1896 and designed by William Crisp. In 1898 the Christie Enclosure was established to house sensitive magnetic instruments that had been disrupted by the use of iron at the main facility. The Observatory underwent an attempted bombing on 15 February 1894. This was possibly the first "international terrorist" incident in Britain. The bomb was accidentally detonated while being held by 26-year-old French
anarchist Anarchism is a political philosophy and Political movement, movement that is sceptical of authority and rejects all involuntary, coercive forms of hierarchy. Anarchism calls for the abolition of the State (polity), state, which it holds to ...

anarchist
Martial Bourdin Martial Bourdin (1868 – 15 February 1894) was a French people, French anarchist, who died on 15 February 1894 when chemical explosives that he was carrying prematurely detonated outside the Greenwich Observatory, Royal Observatory in Greenwich Pa ...
in
Greenwich Park Greenwich Park is a former hunting Hunting is the practice of seeking, pursuing and capturing or killing wildlife or feral animals. The most common reasons for humans to hunt are to harvest useful animal products (meat, fur/hide (skin), hide, ...
, near the Observatory building. Bourdin died about 30 minutes later. It is not known why he chose the observatory, or whether the detonation was intended to occur elsewhere. The novelist
Joseph Conrad Joseph Conrad (born Józef Teodor Konrad Korzeniowski, ; 3 December 1857 – 3 August 1924) was a Polish-British writer regarded as one of the greatest novelists to write in the English language. Though he did not speak English fluently u ...

Joseph Conrad
used the incident in his novel ''
The Secret Agent ''The Secret Agent: A Simple Tale'' is a novel by Joseph Conrad Joseph Conrad (born Józef Teodor Konrad Korzeniowski, ; 3 December 1857 – 3 August 1924) was a Polish-British writer regarded as one of the greatest novelists to write ...
''.


Early 20th century

For major parts of the twentieth century, the Royal Greenwich Observatory was not at Greenwich, because it moved to
Herstmonceux Herstmonceux ( , ) is a village and civil parish In England, a civil parish is a type of administrative parish used for local government. It is a territorial designation which is the lowest tier of local government below districts and c ...
in Sussex in 1957. The last time that all departments were in Greenwich was 1924: in that year electrification of the railways affected the readings of the
Magnetic Magnetism is a class of physical attributes that are mediated by s. s and the s of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Magnetism is one aspect of the combined phenomenon of . The ...

Magnetic
and
Meteorological Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting Weather forecasting is the application of science and technology to predict the ...
Departments, and the Magnetic Observatory moved to
Abinger Abinger is a large, well-wooded and mostly rural civil parish that lies between the settlements of Dorking, Shere and Ewhurst in the district of Mole Valley Mole Valley is a non-metropolitan district, local government district in Surre ...
in Surrey. Prior to this, the observatory had had to insist that the electric trams in the vicinity could not use an earth return for the traction current. After the onset of
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a global war A world war is "a war War is an intense armed conflict between states State may refer to: Arts, entertainment, and media Literatur ...
in 1939, many departments were temporarily evacuated out of range of German bombers, to Abinger,
Bradford on Avon Bradford-on-Avon (sometimes Bradford on Avon or Bradford upon Avon) is a town and civil parish In England, a civil parish is a type of administrative parish used for local government Local government is a generic term for the lowest t ...
,
Bristol Bristol () is a city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routle ...

Bristol
, and
Bath Bath may refer to: * Bathing, immersion in a fluid ** Bathtub, a large open container for water, in which a person may wash their body ** Public bathing, a public place where people bathe * Thermae, ancient Roman public bathing facilities Plac ...
, and activities in Greenwich were reduced to the bare minimum. On 15 October 1940, during
the Blitz The Blitz was a German bombing campaign against the United Kingdom in 1940 and 1941, during the . The term was first used by the British press and originated from the term , the German word for 'lightning war'. The Germans conducted mass ai ...
, the Courtyard gates were destroyed by a direct bomb hit. The wall above the Gate Clock collapsed, and the clock's dial was damaged. The damage was repaired after the war.


The Royal Observatory at Herstmonceux

After the Second World War, in 1947, the decision was made to move the Royal Observatory to
Herstmonceux Castle Herstmonceux Castle is a brick-built castle in East Sussex East Sussex is a county A county is a geographical region of a country used for administrative or other purposesChambers Dictionary, L. Brookes (ed.), 2005, Chambers Harrap ...

Herstmonceux Castle
and 320 adjacent acres (1.3 km2), 70 km south-southeast of Greenwich near
Hailsham Hailsham is a civil parish In England, a civil parish is a type of administrative parish used for local government. It is a territorial designation which is the lowest tier of local government below districts and counties, or their com ...
in East Sussex, due to
light pollution Light pollution is the presence of unwanted, inappropriate, or excessive artificial lighting Lighting or illumination is the deliberate use of light Light or visible light is electromagnetic radiation within the portion of the elect ...

light pollution
in London. The Observatory was officially known as the ''Royal Greenwich Observatory, Herstmonceux''. Although the
Astronomer Royal Astronomer Royal is a senior post in the Royal Households of the United Kingdom. There are two officers, the senior being the Astronomer Royal dating from 22 June 1675; the second is the Astronomer Royal for Scotland dating from 1834. The post ...
Harold Spencer Jones Sir Harold Spencer Jones KBE FRS FRSE Fellowship of the Royal Society of Edinburgh (FRSE) is an award granted to individuals that the Royal Society of Edinburgh, Scotland's national academy of science and Literature, letters, judged to be " ...
moved to the castle in 1948, the scientific staff did not move until the observatory buildings were completed, in 1957. Shortly thereafter, other previously dispersed departments were reintegrated at Herstmonceux, such as the Nautical Almanac Office, Chronometer Department, the library, and observing equipment. The largest telescope at Greenwich at that time, the
Yapp telescope The Yapp telescope is a 36-inch (3 foot / ~91.44 cm) reflecting telescope of the United Kingdom, now located at the Observatory Science Centre at Herstmonceux Herstmonceux ( , ) is a village and civil parish In England, a civil parish is ...
36-inch reflector, was moved out to Herstmonceux in 1958.
/ref> There it was reconstructed in Dome B of the facility. There it was used for astronomy in the 1960s, 1970s, and 1980s. It was left behind at Herstmonceux in 1990 in its dome when the organization moved once again. The tricentennial of
Sir Isaac Newton Sir Isaac Newton (25 December 1642 – 20 March 1726/27) was an English mathematician A mathematician is someone who uses an extensive knowledge of mathematics Mathematics (from Greek: ) includes the study of such topics a ...

Sir Isaac Newton
had passed during the Second World War, delaying festivities. One of the ground-swells was to build a 'big better' telescope in honour of the celebrated inventor of the Newtonian reflecting telescope. Some two decades of development led to the commissioning of the Isaac Newton Telescope at Herstmonceux. It proved so successful that the cloudy weather was felt to be a bottleneck to its productivity, and plans were made to get it to a higher spot with better weather. On 1 December 1967, the
Isaac Newton Telescope The Isaac Newton Telescope or INT is a 2.54 m (100 in) optical telescope A telescope is an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objec ...
of the Royal Greenwich Observatory at Herstmonceux was inaugurated by Queen Elizabeth II. The telescope was the biggest telescope by aperture in the British Isles. It was moved to
Roque de los Muchachos Observatory Roque de los Muchachos Observatory ( es, Observatorio del Roque de los Muchachos, ORM) is an astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands. The observatory site is operated by the In ...

Roque de los Muchachos Observatory
in Spain's
Canary Islands The Canary Islands (; es, Islas Canarias, ), also known informally as ''the Canaries'', is a Spanish archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster or collection of island ...
in 1979. In 1990 the RGO moved to
Cambridge Cambridge ( ) is a university city and the county town In the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' ...

Cambridge
. At Herstmonceux, the castle grounds became the home of the International Study Centre of Queen's University, Kingston, Canada and The Observatory Science Centre, which is operated by an educational charity Science Project. The Observatory Science Centre opened in April 1995. Some of the remaining telescopes, which were left behind in the move, have public observation events as part of operations of the centre. The centre has established itself as a noted tourist and education attraction in its own right, featuring many old observatory items as exhibits. It was getting 60,000 visitors per year in the early 21st century.


The Royal Observatory at Cambridge

In 1990 the Royal Observatory moved from Herstmonceux to a new site at
Cambridge Cambridge ( ) is a university city and the county town In the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' ...

Cambridge
, adjacent to the
University A university () is an educational institution, institution of higher education, higher (or Tertiary education, tertiary) education and research which awards academic degrees in several Discipline (academia), academic disciplines. Universities typ ...
's Institute of Astronomy, where it occupied Greenwich House just to the north of the
Cambridge Observatory Cambridge Observatory is an astronomical observatory at the University of Cambridge in the East of England. It was established in 1823 and is now part of the site of the Institute of Astronomy, Cambridge, Institute of Astronomy. The old Observatory ...
. By now, the RGO's focus had moved from carrying out observations from the British Isles to providing technical support, acting as a conduit between scientists in British universities and the powerful British-owned telescopes (such as the
Isaac Newton Telescope The Isaac Newton Telescope or INT is a 2.54 m (100 in) optical telescope A telescope is an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objec ...
, the Anglo-Dutch
Jacobus Kapteyn Telescope The Jacobus Kapteyn Telescope or JKT is a 1-metre optical telescope named for the Dutch astronomer Jacobus Kapteyn (1851-1922) of the Isaac Newton Group of Telescopes at the Roque de los Muchachos Observatory on La Palma in the Canary Islands, Spai ...
, and the
William Herschel Telescope The William Herschel Telescope (WHT) is a optical Optics is the branch of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science ...

William Herschel Telescope
) on the
Canary Islands The Canary Islands (; es, Islas Canarias, ), also known informally as ''the Canaries'', is a Spanish archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster or collection of island ...
and
Hawaii Hawaii ( ; haw, Hawaii or ) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspape ...

Hawaii
.Charles Arthur, ''A closed subject?''
The Independent, 10 June 1997 (accessed 12 November 2019)
After abandoning a plan to privatise the RGO and the Royal Observatory Edinburgh, the
Particle Physics and Astronomy Research Council The Particle Physics and Astronomy Research Council (PPARC) was one of a number of research council Research funding is a term generally covering any funding for scientific research Research is "creativity, creative and systematic work un ...
(PPARC) as the RGO's funding body made the decision to close the institution and the Cambridge site by 1998. When the RGO was closed as an institution, the
HM Nautical Almanac Office Her Majesty's Nautical Almanac Office (HMNAO), now part of the United Kingdom Hydrographic Office, was established in 1832 on the site of the Royal Observatory, Greenwich The Royal Observatory, Greenwich (ROG; known as the Old Royal Obser ...
transferred to the
Rutherford Appleton Laboratory The Rutherford Appleton Laboratory (RAL) is one of the national scientific research laboratories in the UK operated by the Science and Technology Facilities Council (STFC). It began as the Rutherford High Energy Laboratory, merged with the Atla ...
(
Harwell Science and Innovation Campus The Harwell Science and Innovation Campus is a 700 acre science and technology campus in Oxfordshire, England. Over 6,000 people work there in over 240 public and private sector organisations, working across sectors including Space, Clean Energ ...
, Chilton,
Oxfordshire Oxfordshire is a landlocked county A county is a geographical region of a country used for administrative or other purposesChambers Dictionary The ''Chambers Dictionary'' (''TCD'') was first published by William Chambers (publisher), ...

Oxfordshire
), while other work went to the
UK Astronomy Technology Centre The UK Astronomy Technology Centre (UK ATC) is based at the Royal Observatory in Edinburgh Edinburgh (; sco, Edinburgh; gd, Dùn Èideann ) is the capital city of Scotland and one of its 32 Council areas of Scotland, council areas. Histor ...
in Edinburgh. The old observatory site at Greenwich returned to its original name – the Royal Observatory, Greenwich – and was made part of the
National Maritime Museum The National Maritime Museum (NMM) is a maritime museum in Greenwich, London. It is part of Royal Museums Greenwich, a network of museums in the Maritime Greenwich World Heritage Site. Like other publicly funded national museums in the United ...

National Maritime Museum
. In 2002 the UK joined the
European Southern Observatory The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 me ...
, building the VISTA infrared telescope at the
Paranal Observatory Paranal Observatory is an astronomical observatory operated by the European Southern Observatory (ESO). It is located in the Atacama Desert of northern Chile Chile (, ; ), officially the Republic of Chile (), is a country in western South ...
as an in-kind contribution. The Astronomer Royal
Martin Rees Martin John Rees, Baron Rees of Ludlow, One or more of the preceding sentences incorporates text from the royalsociety.org website where: (born 23 June 1942) is a British British may refer to: Peoples, culture, and language * British peo ...
called PPARC "irresponsible" for how it handled the RGO.


Greenwich site returns to active use

In 2018 the Annie Maunder Astrographic Telescope (AMAT) was installed at the ROG in Greenwich. AMAT is a cluster of four separate instruments, to be used for astronomical research; it had achieved first light (astronomy), first light by June 2018, and contains: * A 14-inch reflector that can take high-resolution images of the sun, moon and planets. * An instrument dedicated to observing the sun. * An instrument with interchangeable filters to view distant nebulae at different optical wavelengths. * A general-purpose telescope. The telescopes and the works at the site required to operate them cost about £150,000, from grants, museum members and patrons, and public donations. The telescope was installed in the Altazimuth Pavilion, from which the multi-purpose telescope is controlled by a computer system.


Magnetic observations

The first magnetic observation was taken in 1680 by the first Astronomer Royal, John Flamsteed, using a magnetic needle from the Royal Society. The second and third Astronomers Royal, Edmond Halley and then James Bradley, also took some magnetic measurements during their tenure. In the 19th century George Airy established the Magnetical and Meteorological Department. The first Magnetic House was built next to the observatory but by 1900 a second, about 300–400 metres from the main observatory, was built to reduce magnetic interference. Both houses were made of non-magnetic materials. The older building was called the Magnet House, but iron added to buildings in the 1890s at the observatory was throwing off measurements, so the instruments were moved to the Magnetic Pavilion. A new Magnetograph House was also completed by 1914. One of the special events that occurred in the study of magnetism was when François Arago and Alexander von Humboldt took magnetic observations at Greenwich in 1822. In 1825 Arago won the Copley Medal, Copley Gold Medal for this research (see also Arago's rotations).


Observatory museum

The observatory buildings at Greenwich became a museum of astronomical and navigational tools, which is part of the Royal Museums Greenwich. Notable exhibits include John Harrison's pioneering marine chronometer, chronometer, known as John Harrison#H4, H4, for which he received a large reward from the
Board of Longitude The Commissioners for the Discovery of the Longitude at Sea, or more popularly Board of Longitude, was a British government body formed in 1714 to administer a scheme of prizes intended to encourage innovators to solve the problem of finding longit ...
, and his three earlier marine timekeepers; all four are the property of the Ministry of Defence (United Kingdom), Ministry of Defence. Many additional horological artefacts are displayed, documenting the history of precision timekeeping for navigational and astronomical purposes, including the mid-20th-century Russian-made F.M. Fedchenko clock (the most accurate pendulum clock ever built in multiple copies). It also houses the astronomical instruments used to make meridian observations and the 28-inch equatorial Howard Grubb, Grubb
refracting telescope 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 de ...
of 1893, the largest of its kind in the UK. The Shepherd Gate Clock, Shepherd Clock outside the observatory gate is an early example of an Clock#Synchronized or slave clocks, electric slave clock. In 1997 the observatory site was getting 400,000 visitors per year. In February 2005 a £16 million redevelopment comprising a new planetarium and additional display galleries and educational facilities was started; the ROG reopened on 25 May 2007 with the new 120-seat Peter Harrison Planetarium. For a year between 2016 and 2017 the Museum reported 2.41 million visitors.


Site


See also

* List of astronomical observatories


References


Further reading

*''Greenwich Observatory: ... the Royal Observatory at Greenwich and Herstmonceux, 1675–1975''. London: Taylor & Francis, 1975 3v. (Vol. 1. ''Origins and early history (1675–1835)'', by Eric G. Forbes. ; Vol. 2. ''Recent history (1836–1975)'', by A.J. Meadows. ; Vol. 3. ''The buildings and instruments'' by Derek Howse. )


External links


Royal Museums Greenwich (RMG) Web site
– includes section on Royal Observatory Greenwich (ROG)
ROG on RMG Web siteOnline catalogue of the Royal Greenwich Observatory Archives (held at Cambridge University Library)"Where the Earth's surface begins—and ends"
''Popular Mechanics'', December 1930
HM Nautical Almanac OfficeAerial View of The Royal Observatory, Greenwich at Google Maps
* [http://www.royalobservatorygreenwich.org/devblog/wp-content/uploads/2015/05/RGO-Herstmonceux-site-plan-c.1967.jpg Map of the Royal Greenwich Observatory at Herstmonceux]
A Personal History of the Royal Greenwich Observatory at Herstmonceux Castle, 1948–1990 by George Wilkins, a former staff memberThe Observatory Science CentreIsaac Newton Group of TelescopesA pictorial catalogue of meridian markers
{{Authority control Royal Observatory, Greenwich, Buildings and structures completed in 1676 Christopher Wren buildings in London Astronomical observatories in England Cultural and educational buildings in London Buildings and structures in the Royal Borough of Greenwich Education in the Royal Borough of Greenwich History of the Royal Borough of Greenwich Grade I listed buildings in the Royal Borough of Greenwich Grade I listed museum buildings Tourist attractions in London Horological museums in the United Kingdom Museums in the Royal Borough of Greenwich Science and technology in London 1676 establishments in England Greenwich Park Buildings containing meridian lines Time balls