Royal Observatory, Greenwich - Wikipedia, the free encyclopedia
"RGO" redirects here. For other uses, see .
Royal Observatory, Greenwich. A
sits atop the Octagon Room.
Flamsteed House in 1824
Royal Observatory, Greenwich c. 1902 as depicted on a postcard
The Royal Observatory, Greenwich, (known as the Royal Greenwich Observatory or RGO when the working institution moved from Greenwich to
after World War II) played a major role in the history of
and , and is best known as the location of the . The observatory is situated on a hill in , overlooking the .
The observatory was commissioned in 1675 by , with the
being laid on 10 August. The site was chosen by . At that time the king also created the position of , 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
as the first AR. 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 as a museum.
1675 Royal Observatory founded.
established the
and . The Astronomer Royal was, until the Board was dissolved in 1828, always an ex officio Commissioner of Longitude.
1767 Astronomer Royal
began publication of the , based on observations made at the Observatory.
1818 Oversight of the Royal Observatory was transferred from the
to the B at that time the observatory was charged with maintaining the Royal Navy's .
1833 Daily time signals began, marked by dropping a .
1899 The New Physical Observatory (now known as the South Building) was completed.
1924 Hourly time signals () from the Royal Observatory were first broadcast on 5 February.
1948 Office of the Astronomer Royal was moved to Herstmonceux.
1957 Royal Observatory completed its move to Herstmonceux, becoming the Royal Greenwich Observatory (RGO). The Greenwich site is renamed the Old Royal Observatory.
1990 RGO moved to Cambridge.
1998 RGO closed. Greenwich site is returned to its original name, the Royal Observatory, Greenwich, is made part of the .
Former Royal Greenwich Observatory, , East Sussex
Greenwich Observatory (Latinized as "Observatorium Anglicanum Hoc Grenovici prope Londinum"), as illustrated in 's map of the , ca. 1730
There had been significant buildings on this land since the reign of William I. , near the site of the present-day Maritime Museum, was the birthplace of Henry VIII;
used , which stood on the land that the Observatory presently occupies. 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.
Laser projected from the observatory marking the
Laser at night
The establishment of a Royal Observatory was proposed in 1674 by Sir
who, in his role as Surveyor General at the Ordnance Office, 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 , probably assisted by , 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, which resulted in the alignment being 13 degrees away from true North, somewhat to Flamsteed's chagrin.
The original observatory at first housed the scientific instruments to be used by Flamsteed in his work on stellar tables, and over time also incorporated additional responsibilities such as marking the official time of day, and housing .
Moore donated two clocks, built by , 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.
Main article:
The 24-hour
Telescope and tree
Royal Observatory, Greenwich
One of the hyper-accurate timekeepers at the observatory
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 , the meridian that passes through the
, first used in 1851, was adopted as the world's
on 22 October 1884. Subsequently, nations across the world used it as their standard for mapping and timekeeping. The Prime Meridian was marked by a brass strip (presently upgraded to ) 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
shining north across the London night sky.
in the period ,
maps have been based on an earlier version of the Greenwich meridian, defined by the transit instrument of . 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
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 8m) 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
(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
called a , 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
and the , use a single oblate spheroid, fixed to the Earth's gravitational centre. The shift from several 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 102.5 metres east of the Greenwich astronomical meridian represented by the stainless steel strip. Thus the strip is now 5.31
West. The modern location of the Airy Transit is
International time since the end of the 19th century (before ) was based on 's equations, giving a mean sun about 0.18 seconds behind UT1 (the equivalent of 2.7 arcseconds) as of 2013; it coincides in 2013 with a meridian halfway between Airy's circle and the  : .
Main article:
(GMT) was until 1954 based on celestial observations made at Greenwich. Thereafter, GMT was calculated from observations made at other observatories. GMT is more properly called
at present, and is calculated from observations of extra-galactic radio sources, and then converted into several forms, including UT0 (UT at the remote observatory), UT1 (UT corrected for ), and
(UT in discrete
seconds within 0.9 s of UT1).
To help others synchronise their clocks to GMT, AR
installed atop the observatory in 1833. It still drops daily to mark the exact moment of 1 pm (13:00) year-round (GMT during winter and
during summer).
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
in , 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. Novelist
used the incident in his novel .
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Standard lengths on the wall of the Royal Observatory, Greenwich, London – 1 yard (3 feet), 2 feet, 1 foot, 6 inches (1/2 foot), and 3 inches. The separation of the inside faces of the marks is exact at an ambient temperature of 60 °F (16 °C) and a rod of the correct measure, resting on the pins, will fit snugly between them.
During most of the twentieth century, the Royal Greenwich Observatory was not at Greenwich. The last time that all departments were there was 1924: in that year electrification of the railways affected the readings of the
Department and forced its move to . Indeed, prior to this, the observatory had to insist that the electric trams in the vicinity could not use an earth return for the traction current. After the onset of
in 1939, many departments were evacuated, along with the rest of London, to the countryside (Abinger, , and ) and activities in Greenwich were reduced to the bare minimum.
After the War, in 1947, the decision was made to move to
and 320 adjacent acres (1.3 km?), 70 km south-southeast of Greenwich near
in East Sussex, due to
in London. Although the
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.
was built at Herstmonceux in 1967, but was moved to
in Spain's
in 1979. In 1990 the RGO moved again, to . Following a decision of the , it closed in 1998.
was transferred to the
after the closure. Other work went to the
in Edinburgh. The castle grounds became the home of the International Study Centre of
and The Observatory Science Centre, which is operated by an educational charity .
At present the observatory buildings at Greenwich include a museum of astronomical and navigational tools, which is part of the , notably including 's , , which received a large reward from the , and his three earlier marine timekeepers, although all four are the property of the . 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
of 1893, the largest of its kind in the UK. The
outside the observatory gate is an early example of an . In February 2005 construction began on a ?15 million redevelopment project to provide a new
and additional display galleries and educational facilities. The 120-seat
opened on 25 May 2007.
It currently possesses the
observatory code of 000.
Robert Chambers, Book of Days
John Timbs' Abbeys, Castles and Ancient Halls of England and Wales
Hart, Kelly (2010), The Mistresses of Henry VIII, The History Press, p. 73,  
Willmoth, Frances (2004). "Moore, Sir Jonas ()".
(online ed.). Oxford University Press. :. (Subscription or
required.)
Dolan, Graham. . The Greenwich Meridian 2015.
Howse, Derek (1997). Greenwich time and the longitude. London: Phillip Wilson. p. 12.  .
Howse, Derek (1980). . p. 171.
Adams, Brian (1994).
(PDF). pp. 14–15.
Malys, S Seago, John H.; Palvis, Nikolaos K.; Seidelmann, P. K Kaplan, George H. (1 August 2015). . Journal of Geodesy. :.
Seago, John H.; Seidelmann, P. Kenneth.
(PDF). Paper presented at the AAS/AIAA Spaceflight Mechanics Meeting, Kauai, HI, USA, March 2013. Reprinted from Advances in the Astronomical Sciences v. 148. pp. , 1805.
Bennett, Keith (2004), Bucher, Jay L., ed., The Metrology Handbook, Milwaukee, WI: American Society for Quality Measurement, p. 8,  .
Walford, Edward (1878),
. Minor Planet Center 2013.
Greenwich Observatory: ... the Royal Observatory at Greenwich and Herstmonceux, . London: Taylor & Francis, 1975 3v. (Vol. 1. Origins and early history (), by Eric G. Forbes. ; Vol. 2. Recent history (), by A.J. Meadows. ; Vol. 3. The buildings and instruments by Derek Howse. )
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