Royal Observatory Greenwich, London

Aerial photography of the Royal Observatory, Greenwich

Aerial photography of the Royal Observatory, Greenwich. © National Maritime Museum.

The Royal Observatory Greenwich (ROG) is part of Royal Museums Greenwich, also comprising the National Maritime Museum (NMM), The Queen’s House and Cutty Sark. Each reveals the royal and maritime influences on Greenwich, and each has elements of interest to historians of science. The buildings, dating from the 17th to 19th centuries, with many more recent additions and alterations, border and are contained within a Royal Park and the Maritime Greenwich World Heritage Site.

The science associated with Greenwich was very largely done for maritime purposes. It was practical, utilitarian and concerned with precision, accuracy and standards rather than the production of new knowledge. Few scientific discoveries can be associated with the Observatory, but its importance to the history of astronomy, timekeeping, navigation and cartography is demonstrated by the fact that, ultimately, the world’s standard reference point for time and position – the Prime Meridian – came to be the meridian on which the ROG’s chief instrument was set.

The Royal Observatory was founded in 1675 with the remit of improving astronomical tables in order to aid maritime navigation, specifically to support the lunar distance method for finding longitude (east-west position). Predicting the motions of the moon turned out to be an even harder problem than anticipated, and it was not until the 1760s that the ROG fulfilled its remit, when observations began to feed into the Nautical Almanac.

A complementary method of finding longitude at sea, using a timekeeper that could keep time at a regular rate over the course of a long voyage, matured at the same time. Once sea watches, or chronometers, became sufficiently numerous and affordable, the Astronomer Royal was charged with testing, rating and distributing them for the Royal Navy. Thus both the astronomical and timekeeping methods of finding longitude were supported by the work of the Observatory.

The ROG was a leading institution in the development of precision, meridian astronomy. The Astronomers Royal commissioned London’s top instrument and clock makers, the Observatory’s equipment and routines were hugely influential and its output was generally accepted as the most thorough and reliable. The work of John Flamsteed, James Bradley and Nevil Maskelyne was seen as core to Britain’s reputation in practical astronomy.

In the 19th century work at the ROG began to diversify. Magnetic and meteorological observations were begun, the distribution of time for civilian purposes became increasingly important and new techniques, particularly photography and spectroscopy, were introduced. Despite some new research, Greenwich largely focused on providing services for navigation and astronomy and on long-term programmes of data collection.

The buildings of the ROG, much extended and altered over the years, reveal this history. The oldest is Flamsteed House, the first floor and basement of which was home to the Astronomers Royal and their families until the institution moved to Herstmonceux in Sussex after the Second World War. On the first floor is the Octagon Room, built to house and test the going of Thomas Tompion’s experimental clocks, but thereafter largely used for storage and as a meeting room.

The real observatory was the series of buildings that housed the meridian instruments. Flamsteed’s original meridian observatory, which housed his mural arc, was built over several times, so the series of buildings that exists today is that begun by Bradley in the 1740s to house the quadrants, transit telescope, clocks and assistant astronomer. These buildings were extended several times as new instruments and additional work space was required. Some additions were removed when the Observatory was transformed into a Museum in the 1960s.

Greenwich Observatory

Greenwich Observatory by heatheronhertravels. Image licensed under Creative Commons Attribution-NoDerivs 2.0 Generic license.

Many of the original instruments of the Observatory survive and have been set up largely in their original locations, providing a timeline toward the Airy Transit Circle (1851), which defined the international Prime Meridian.

Adjoining the meridian buildings is the Great Equatorial Building (1857), today housing the second of the two large equatorial telescopes that were mounted there in the 19th century. It marks a clear development of the Observatory’s work away from an exclusive focus on meridian astronomy. Below the telescope are rooms in which the Navy’s chronometers were tested and stored. Today they contain the office and workshop (visible through a glass wall) of the Museum’s horologists.

The Observatory’s site continues southwards from here, towards an area added in the 1830s. Until the end of the century, this contained the Magnetic Observatory, which was later moved out into an enclosure within Greenwich Park and, in the 1920s, to Abinger. The buildings that remain date from the 1890s: the Altazimuth Pavilion, originally containing an altazimuth telescope, and the South Building. Originally called the New Physical Observatory, this housed three large telescopes, darkrooms, record and instrument stores, workshop and the office space for a much enlarged staff.

Today, the displays at the ROG fall into three categories. Firstly, the Astronomer’s Apartments and the Octagon Room in Flamsteed House have been dressed to suggest their original 17th-century appearance, while the Meridian Building displays the remounted 18th- and 19th-century instruments. Secondly, there are galleries that focus on the history of timekeeping: the story of longitude, the Navy’s chronometers, the dissemination of Greenwich Mean Time, and personal timekeeping. Thirdly, the South Building houses galleries dedicated to interactive exhibits and modern astronomy and adjoins a purpose-built planetarium.

As well as many of the Observatory’s original instruments, the ROG’s displays benefit from astronomical, navigational and cartographic collections acquired by the NMM from the 1930s onward. Descriptions of all objects and artworks in the collections are available online. The archives of the ROG itself are now held at Cambridge (which is where the institution ended up before its closure in 1998) but the Museum’s Caird Library and Archive contain relevant books and manuscripts, including the Airy Collection of rare books formerly belonging to the Observatory.

Further reading

A brief introduction to the history of the ROG can be found on its website, but the most thorough history is the three volumes by Eric G. Forbes, A. J. Meadows and Derek Howse: Greenwich Observatory. Howse is also author of the very useful Greenwich Time and Longitude. For an illustrated snapshot of what the Observatory was like at the end of the 19th century see E. Walter Maunder’s The Royal Observatory, Greenwich: a Glance at its History and Work.

There are four important catalogues showcasing some of the most significant scientific instrument collections: Astrolabes, Sundials, Globes and Sextants. A fifth, dedicated to Chronometers, is in progress.

Paris Observatory, France

Paris Observatory

Paris Observatory by Joerg Weingrill. Image licensed under Creative Commons Attribution 2.0 Generic license.

The Paris observatory dates back to the ambitious days of Louis XIV and his chief minister Colbert. It was completed in 1672; its four walls are oriented precisely to the four points of the compass; the southern wall defines the nominal latitude of the city and a perpendicular line through the center of the building defines the “Paris meridian.” The actual numerical coordinates, relative to other places on earth, were established with the aid of the Danish astronomer Ole Remer, brought here by Colbert because he had inherited the mantle of Danish expertise that had been established a century earlier by Tycho Brahe. Remer remained in Paris for several years and it was here that he accomplished his main scientific achievement, the measurement of the speed of propagation of light, in 1676~ The event is marked by one of the official city plaques placed on the observatory wall. Christiaan Huygens from the Netherlands was here for several years in the same period and was the first to see the rings about the planet Saturn.

In front of the observatory entrance is a statue of the French astronomer LeVerrier, effectively the discoverer of Neptune, the eighth planet of the solar system. The seventh planet, Uranus, had first been sighted by William Herschel in England in 1781, but irregularities in its orbital motion suggested the existence of a more distant planet beyond. LeVerrier in 1846 predicted its orbit on the basis of mathematical calculations and the prediction, of course, included its “present” location. A German observer O. C. Galle) found it where predicted on the very next day-the instruments at the Paris observatory lacked the requisite precision. (This was probably the first discovery of an object in sky on the basis of calculation, which has now become commonplace.)

Tastrup, Denmark

Sunset in Taastrup

Sunset in Taastrup by Björn Söderqvist. Image licensed under Creative Commons Attribution-NoDerivs 2.0 Generic license.

Ole Remer was born in Arhus (in Jutland), where a street is named after him, but the most important memorial is a national one at Vridslesemagle, just north of the town of Tastrup, where the remains of Remer’s old observatory were uncovered in 1978. The site has been converted into a monument, with a fine statue of the astronomer, his eyes raised proudly to the skies. There is a museum about 1,000 feet (300 m) away. It is an impressive place despite operating on a shoestring budget, with good explanations of the instruments Remer devised and why some of them were better than Tycho Brahe’s a hundred years earlier and why they are not as good as instruments we have today. Some modem astronomical devices are shown as a basis for comparison. Star gazing evenings open to the public are held here once a week during the winter.

The most spectacular items in the museum are replicas of the “Planetarium” and the “Eclipsareon,” two instruments designed by Remer during his stay in Paris and constructed for him by the Paris clockmaker Isaac Thuret. The planetarium is the first device of its kind that was built according to the Copernican heliocentric system, with the earth as one of the planets circling the sun. The eclipsareon shows the motions of the moon, earth, and sun. Its unique feature is that it includes offset cams, by means of which the elliptical path of the moon and the varying speed of its motion can be represented. Both models are in perfect mechanical order and can be put in motion by the visitor, by turning a handle in one case and by means of an electric motor in the other.

The two machines were immensely popular in Remer’s lifetime and many copies were made. Jesuit missionaries took copies in the 1680s to the shah of Persia, the king of Siam and the emperor of China. They were especially appreciated in China, where lunar and solar eclipses were central to religious festivals and the ability of the eclipsareon to predict them accurately was thus a great boon. Remer’s original planetary engines fell into disuse after his death. Their mechanism rusted, their metal was vandalized, and they were moved to the Round Tower in Copenhagen, where they were destroyed by Copenhagen’s great fire of 1728, when one third of the city went up in flames.

The Vridslølsemagle site was picked out by Remer himself in 1704, and it is still obvious today why one would want to put an observatory here. The ground is slightly elevated (by Danish standards), with picturesque farmland on all sides. The sky in good weather is crisply clear, and in 1704 sky is all you would have seen at night for miles around. Today, of course, the lights of Copenhagen blot out the stars toward the east. (It should be noted that the observatory foundations were built below ground level for optimal stability and were lost for more than 200 years. It proved no easy task to locate the remains in 1978.)

Norman Lockyer Observatory, Devon, England


Norman Lockyer Observatory and James Lockyer Planetarium

Norman Lockyer Observatory and James Lockyer Planetarium, by Paul Lang. Image licensed under Creative Commons Attribution-ShareAlike 2.0 UK: England & Wales license.

The Norman Lockyer Observatory is situated on Salcombe Hill to the east of Sidmouth off the road from Sidmouth to Salcombe Regis. It is owned by the East Devon District Council but is operated on a voluntary basis by and for the members of the Norman Lockyer Observatory Society. Its principal facilities include three Victorian refracting telescopes and two modern reflectors, a planetarium, equipment for amateur radio reception and transmission, a meteorological station, an exhibition area, a library and a lecture theatre.

The Observatory is not constantly manned but is open to the public at listed times (mainly on Saturday evenings and Wednesday afternoons) and for prearranged visits by schools and other groups. There are guided tours of the telescopes, with observing when the conditions are suitable, and presentations of the planetarium. There are occasional special events and an annual Astronomy Fair, with trade stands and lectures by eminent astronomers as well as tours and planetarium presentations, in early August. There are charges for these visits and events.

A brief history of the period 1912 to 1989

Norman Lockyer was a Victorian amateur astronomer who became the director of the Solar Physics Observatory at South Kensington and the first professor of astronomical physics in the Normal School of Science (now the Royal College of Science) in 1887. He was knighted in 1897. His second marriage in 1903 was to a widow who had inherited land in Sidmouth where they built a retirement home in 1910. On the suggestion of Francis McClean, the son of the wealthy amateur astronomer Frank McClean, Lockyer obtained support in 1912 for the building of the Hill Observatory on the hill above the Lockyer house. McClean donated a telescope from his father’s observatory at Tunbridge Wells and Lockyer obtained a telescope that was no longer required by the Solar Physics Observatory, which was to be moved to Cambridge. They and others also donated money and other equipment. The Hill Observatory Corporation was established in 1916.

The activities largely ceased during the 1914-1918 war, but were resumed in 1919 when Lockyer’s son James was released from his duties in the Royal Air Force and Donald Edwards was appointed as an assistant. Sir Norman Lockyer died in 1920, the Observatory was renamed in his honour and James became the Director. The McClean Telescope has 10-inch visual and 12-inch photographic refractors and while the Kensington Telescope has 10-inch and 9-inch refractors; both were used largely for stellar spectroscopic observations. The Mond Dome and Telescope were funded by Sir Robert Mond, who was then the chairman of the Corporation, and were inaugurated in 1932. The telescope actually consisted of four separate cameras of different focal lengths that were used mainly for survey purposes.

James Lockyer died suddenly in 1936 and was succeeded by Edwards, who was then assisted by Donald Barber. Observations were interrupted by the 1939-1945 war. Lady Lockyer died in 1943 and bequeathed her house and land to the Corporation. Nevertheless the funds of the Corporation were very low, but the University College of the South West of England (now the University of Exeter) agreed to support the astronomical activities. Edwards died in 1956 and was succeeded by Barber who retired in 1961. Astronomical observations then ceased and the site was used by the Department of Physics at the University for geophysical observations until about 1980. The University, which controlled but did not own the Corporation, wished to sell the site for development, but this was thwarted when the domes were listed as of historic interest. The site was eventually bought by the East Devon District Council in 1986. It was able to sell the outbuildings for private use and some land was sold to the National Trust following a local Landscape Appeal. The Council was then able to refurbish the site and to extend the Mond Dome to provide facilities for use by the Sidmouth and District Astronomical Society and the Sidmouth Amateur Radio Society under the terms of a Trust Fund.

Developments after 1989

Norman Lockyer Observatory, Sidmouth

Norman Lockyer Observatory, Sidmouth, by David Stowell. Image licensed under Creative Commons Attribution-ShareAlike 2.0 license.

The Observatory was formally reopened by Patrick Moore on 28 October 1989. Unfortunately the Mond Telescope had been vandalised, but the Dome was used for public presentations by a GoTo planetarium that had been obtained from St Luke’s College in Exeter. Both societies flourished and the Astronomical Society had to hold its main monthly meeting at the Arts Centre in Sidmouth as the meeting room at the Observatory became too small. A grant was obtained for the purchase of a CCD-camera and computer system so that the McClean Telescope could be used show live images on a TV screen to visitors. Moreover the number of open periods for visits by the public and schools exceeded the expectations of the Council. It agreed to provide a large extension to the Mond building to include an entrance and exhibition area, a large dome for the James Lockyer Planetarium, an extra room for the Radio Society, as well as toilet facilities and a kitchen. This new facility was opened by Patrick Moore on 29 September 1995.

At this time the two societies merged to form the Norman Lockyer Observatory Society as a company limited by guarantee and with the status of an educational charity. The activities expanded to include meteorology and an observing station; local statistics and images from satellites are shown during open periods. The Mond Dome was used for the telescope that Lockyer had used as an amateur; it was re-inaugurated by Heather Couper, a national TV personality, in 1996. A 12-inch computer-controlled reflector was installed in the new Victoria Dome, which was opened by Craig Rich, a local TV meteorologist, in 1999. The Donald Barber lecture theatre was added to the main building and was formally opened in 2006. It is used for Society meetings, introductory talks to visitors and occasionally by other organisations. The GoTo planetarium projector was replaced by a Spitz projector from the Royal Observatory at Greenwich. A new dome is under construction for a 20-inch reflector that was given to the Observatory a few years ago.

Further information

Address: Norman Lockyer Observatory, Salcombe Hill Road, Sidmouth, Devon, EX10 0NY, England

Institute of Astronomy, University of Cambridge

Early Astronomy in Cambridge

A 19th century view of the Cambridge Observatory

A 19th century view of the Cambridge Observatory

Astronomers have made their home in Cambridge since medieval times. John Holbrook, Master of Peterhouse, Cambridge (1418-36) compiled the ‘Tabulae Cantabrigienses’ for 1430 and C. Kyngeston a Fellow of Peterhouse made observations on the eclipse of the sun in Cambridge on 24 May 1517.  Still perhaps the most famous scientist to study in Cambridge was Sir Isaac Newton, who as a Fellow of Trinity College compiled his famous work the ‘Principia Mathematica’ published in 1687.

In 1704 the Rev. Thomas Plume left money in his will for a chair of astronomy, which became known as the Plumian Professorship.  The Plumian professor had access to an observatory built on to the Gate House of Trinity College from 1739 to 1797, and another observatory existed from 1765 to 1859 at St. Johns College [1].  However, there was a need for a modern observatory on a good site away from the smoke of the town.

The Cambridge Observatory

The Cambridge Observatory was established on the western outskirts of Cambridge in 1823.  It was funded half by the University of Cambridge and half by public subscription.  Of the money raised, the largest sum was spent on the impressive neo-classical observatory building.  Money was then needed for instruments and for staff.

The Observatory was supervised by the Plumian Professor of Astronomy, who in turn reported to a University committee known as the Observatory Syndicate.  The Professor was provided with a house forming the east wing of the building.  The first Plumian Professor to take residence was Robert Woodhouse (1773-1827).  Woodhouse had published ‘An elementary treatise on astronomy’ in 1812, but by the time the Observatory had opened, he was already ill and died in December 1827.  The first effective Director of the Observatory was therefore G. B. Airy (1801-1892), who succeeded to the Plumian Chair.  Airy played a significant role in obtaining the Northumberland Telescope in 1838, a 12-inch refractor still present in a dome in the grounds [2].

The Neptune Affair

When Airy left Cambridge to take up his post as Astronomer Royal in 1835, his successor as Plumian Professor and Director of the Cambridge Observatory was James Challis (1803-1882).  Challis lived at the Observatory until 1861.  In 1846 Challis carried out with the Northumberland Telescope a systematic search for a new planet, on the basis of calculations provided by John Couch Adams.  On the continent, the planet later to be called Neptune, was predicted by Urbain Jean Joseph Le Verrier (1811-1877) and discovered by J. G. Galle (1812-1910) and Heinrich Louis d’Arrest (1822-1875) on the night of 23 September 1846 at the Berlin Observatory.  Key to the success of Galle and d’Arrest was the possession of the star chart (Hora XXI Aquarius) of the Berlin Academy Star Atlas of Carl Bremiker.  This chart of the atlas had been printed in 1845 but had not yet been distributed.  It allowed Galle and d’Arrest to find the planet rapidly, whilst Challis had to map every star in the area [3].

John Couch Adams (1819-1892)

The Northumberland Telescope dome when new

The Northumberland Telescope dome when new.

Adams, is of course best known for having predicted the position of the planet later called Neptune independently of Urbain Le Verrier in 1846.  In 1861 as Lowndean Professor, he also became Director of the Cambridge Observatory and took up residence in the East wing [4].  In 1884 he represented Britain at the international conference that decided on Greenwich as the Prime Meridian of the world.

Sir Robert Ball (1840-1913)

On the death of John Couch Adams in 1892, Robert Ball, famous as an author and popular speaker in astronomy, took over as Director of the Observatory with the position of Lowndean Professor.  Ball also moved into the house on the East wing of the Observatory which he extended.

Sir Arthur Eddington (1882-1944)

Eddington was Plumian Professor from 1913 to 1944 and lived in the Observatory until his death in 1944.  He is famous for having promoted relativity theory in the English-speaking world and proving it right with his 1919 eclipse expedition [5].  Indeed Einstein came to stay at the Observatory with Eddington in 1930.

The Solar Physics Observatory

The Solar Physics Observatory (SPO) was established in South Kensington in the 1870’s.  It had been shaped by Sir Norman Lockyer, who was very closely involved with it until 1913.  In 1913 the Solar Physics Observatory moved to Cambridge to a site adjacent to the Cambridge Observatory and in 1946 it was combined with the University Observatory to become the ‘University Observatories’.

The Institute of Theoretical Astronomy (IOTA)

The Institute of Theoretical Astronomy was the brainchild of Sir Fred Hoyle (1915-2001).  Fred Hoyle coined the term ‘Big Bang’ despite bitterly opposing the theory.  He pioneered the theory of the nucleosynthesis of elements in stars.  Hoyle was a controversial figure, with his theory of life in the universe and his science-fiction books.  The Institute was established in 1967 with a small group of Hoyle’s associates.  An article by John Walsh describes the political background to the founding of the Institute.  It was to concentrate on theory, with no teaching responsibilities and with access to a computer.  It had its own building with library set in the Cambridge Observatory grounds [6].

The Institute of Astronomy (IoA)

Statue of Fred Hoyle in IoA grounds

Statue of Fred Hoyle in IoA grounds

The Institute of Astronomy was created on 1st August 1972 by the amalgamation of the Cambridge Observatories and the Institute of Theoretical Astronomy. The IoA is one of the largest centres for astronomical research in the UK, with about 140 astronomers.  Active areas of research are cosmology, gravitational lensing, X-ray astronomy, galactic astronomy, clusters, stellar physics and instrumentation.  Most observations are made with mountain-top or space telescopes, but some observations are still made on-site.

Over the years, many famous astronomers, including Stephen Hawking, have worked at the Institute. The current Plumian Professor and Director of the IoA is Robert C. Kennicutt from Arizona whose interest is in extragalactic observational astronomy.  Lord Rees, the current President of the Royal Society also has an office at the Institute.

In November 2009 the Kavli Institute for Cosmology Cambridge opened on our site as a joint centre with other Cambridge departments with an interest in observational cosmology.


In 1990 the Royal Greenwich Observatory was moved from Herstmonceux Castle in Sussex to a new building directly behind the Cambridge Observatory.  A glass-walled corridor room provided a link between the two buildings.  The government closed the Royal Greenwich Observatory in 1998.

The Library

The library has existed as part of the Observatory since 1823, although it contains many books which are far older.  A separate history of the Cambridge Observatory Library containing much history of the Observatory has been published by the author [7].

Thorrowgood Telescope

This 8-inch refracting telescope made by Cooke & sons in 1864 went through a series of wealthy amateur owners before arriving in Cambridge in 1929.  It belongs to the Royal Astronomical Society, from whom it is nominally on loan to the University.


To arrange a group or individual visit please contact Mark Hurn, Departmental Librarian, Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA tel. 01223 337537 or email hurnm AT


  1. F. J. M. Stratton, The History of the Cambridge Observatories, Annals of the Solar Physics Observatory, Cambridge, 1, 1949.
  2. W. Airy (editor) Autobiography of Sir George Biddell Airy,  (Cambridge University Press), 1896.
  3. D. Jones, Highlights of Astronomy, 12, 367-370, 2002.
  4. H. M. Harrison, Voyager in space and time, (Book Guild, Sussex), 1994.
  5. D. S. Evans, The Eddington Enigma, (Princeton), 1998.
  6. J. Walsh, Science, 157, 1286-1288, 1967.
  7. M.D. Hurn, The Observatory, 124, 37-46, 2004. Issue 6(04/2010)

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