Chronology • 1675 – 22 June, The Royal Observatory founded by
Charles II. • 1675 – 10 August, construction began. • 1714 - The
Longitude Act established the
Board of Longitude and
Longitude rewards. 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 began publication of
The Nautical Almanac, based on observations made at the Observatory. • 1818 - Oversight of the Royal Observatory was transferred from the
Board of Ordnance to the
Board of Admiralty; at that time the observatory was charged with maintaining the Royal Navy's
marine chronometers. • 1833 - Daily time signals began, marked by dropping a
time ball. • 1838 -
Sheepshanks equatorial, a aperture
refracting telescope installed. • 1852 - Time signals were distributed through telegraph lines. • 1899 - The New Physical Observatory (now known as the South Building) was completed. • 1924 – Hourly time signals (
Greenwich Time Signal) from the Royal Observatory were first broadcast on 5 February, originally generated from a
Dent astronomical regulator (Dent no. 2016). • 1931 -
Yapp telescope ordered. • 1948 - Office of the Astronomer Royal was moved to
Herstmonceux in
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. • 1984 - The
IERS Reference Meridian replaces the Greenwich Meridian as the Prime Meridian for the world. Its location is closely related to its predecessor, but runs approximately 102 metres east of it. • 1990 - RGO moved to
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. • 2011 - The Greenwich museums, including the ROG, became collectively the
Royal Museums Greenwich.
Site 's map of the
southern celestial hemisphere, There had been significant buildings on this land since the reign of William I.
Greenwich Palace, on the site of the present-day
National Maritime Museum, was the birthplace of both
Henry VIII and his daughters
Mary I and
Elizabeth I;
the Tudors 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 who, in his role as
Surveyor-General of the Ordnance, 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, probably assisted by
Robert Hooke, 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, 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 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 and
Board of Longitude) 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, 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 Transit Circle at the Royal Observatory, Greenwich, used for over a century (1851–1953) as the reference point when charting the heavens and determining times, thus earning for it the epithet "the centre of time and space" When the observatory was founded in 1675, one of the best star catalogues was
Tycho Brahe's 1000-star catalogue from 1598. However, this catalogue was not accurate enough to determine longitudes. In the early 19th century, the main positional devices were the Troughton Transit instrument and a
mural circle, but after
George Biddell Airy took over as Astronomer Royal in 1835, he embarked on a plan to have better instruments at Greenwich observatory.
Positional astronomy was one of the primary functions of Greenwich for the
Admiralty. 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. Sources of error include the precision of the instrumentation, and then there has to be accounting for
precession,
nutation, and
aberration. Sources of error in the instrument have to be tracked down and accounted for to produce more accurate results. By observing the transit in combination with timing it and taking measures, a diameter for the planet was taken. The basis of
longitude, the meridian that passes through the
Airy transit circle, first used in 1851, was adopted as the world's
Prime Meridian at the
International Meridian Conference at
Washington, DC, 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) 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 shining north across the London night sky. Since the
first triangulation of Great Britain in the period 1783–1853,
Ordnance Survey maps have been based on an earlier version of the Greenwich meridian, defined by the transit instrument of
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 2.3 m). 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 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 and the
International Terrestrial Reference Frame, 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 is the
IERS Reference Meridian, in full the International Earth Rotation and Reference Systems Service Reference Meridian (in short called the IRM), which is 102.5 metres east of the Airy Greenwich astronomical meridian represented by the stainless steel strip, which is now 5.31
arcseconds 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 was based on
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 at the gates of the Royal Greenwich Observatory. This clock shows
Greenwich Mean Time all year round, ie. it is not set to
British Summer Time in the summer. A key instrument for determining time was the Airy Transit Circle (ATC), which was used primarily from 1851 to 1938. It was agreed that the (Prime) "meridian line marked by the cross-hairs in the Airy Transit Circle eyepiece would indicate 0° longitude and the start of the Universal Day". (Note, however, that this Prime Meridian is obsolete; the
ITRF Zero Meridian, which is more than 100 metres east, is the modern standard defining longitude.) The time was determined by marking the time a star of known location would pass through the aimpoint of the telescope. In 1929, UT was redefined as a statistical combination of multiple observatories. In 1948, the Office of the Astronomer Royal was moved to
Herstmonceux in East Sussex and in 1957, the observatory closed, ceasing time measurement operations. The term "GMT" continues to be promoted by the Observatory and the UK in general, despite no longer being measured in any way.
Coordinated Universal Time (UTC) forms the basis of modern civil time, and is based on the best attributes of UT1 (the modern form of UT, now measured from extra-galactic radio sources) and
International Atomic Time (TAI, time kept by hyper-accurate clocks).
Greenwich Time Ball is the red ball on a post – when it drops a certain time is signalled. The red
time ball of Greenwich was established in 1833, and is noted as a public time signal. 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. 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 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 new dome was made by
T. Cooke and Sons. It was donated to the observatory in the 1880s, but was taken down in the 1890s. 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 Martial Bourdin in
Greenwich Park, 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 used the incident in his 1907 novel
The Secret Agent.
Early 20th century For major parts of the twentieth century, the Royal Greenwich Observatory was not at Greenwich, because it moved to
Herstmonceux in East 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 and
Meteorological Departments, and the Magnetic Observatory moved to
Abinger 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 in 1939, many departments were temporarily evacuated out of range of German bombers, to Abinger,
Bradford on Avon,
Bristol, and
Bath, and activities in Greenwich were reduced to the bare minimum. On 15 October 1940, during
the Blitz, 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 , East Sussex After the Second World War, in 1947, the decision was made to move the Royal Observatory to
Herstmonceux Castle and 320 adjacent acres (1.3 km2), 70 km south-southeast of Greenwich near
Hailsham in East Sussex, due to
light pollution in London. The Observatory was officially known as the
Royal Greenwich Observatory, Herstmonceux. Although the
Astronomer Royal Harold Spencer Jones 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. There it was reconstructed in Dome B of the facility. The tricentennial of 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 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 in Spain's
Canary Islands in 1979. In 1990 the RGO moved to
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. It was getting 60,000 visitors per year in the early 21st century. After abandoning a plan to privatise the RGO and the
Royal Observatory Edinburgh, the
Particle Physics and Astronomy Research Council (PPARC) as the RGO's funding body made the decision to close the institution and the Cambridge site by 1998.
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 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 ==