Tales of London

Greenwich Park and its environs have long held an association with the stars, firstly metaphorical and latterly literal. Greenwich Palace, now the site of the National Maritime Museum, was the birthplace of Henry VIII and his daughters, Mary I and Elizabeth I. Greenwich Castle, atop a hill in the park, was founded as the fifteenth-century Duke Humphrey’s Tower; it was then used as a hunting lodge by the Tudors, where Henry would stow away his mistresses. On the site of the castle now stands a place which defines time itself: the Royal Observatory, Greenwich.

As international trade was developing across the Atlantic in the seventeenth century, the issue of longitudinal navigation was becoming increasingly important. Since classical times the position of the stars had been used to calculate a ship’s line of latitude north or south of the equator, but there was no reliable method for calculating how far east or west one had travelled. In 1674 Sir Jonas Moore, the Surveyor-General of the Ordnance, proposed to Charles II that an observatory be established, with an Astronomer Royal appointed 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.” 

Charles gave his consent the following year, with Sir Christopher Wren in charge of constructing the observatory, himself a former Savilian Professor of Astronomy at Oxford. Known as Flamsteed House after the first Astronomer Royal John Flamsteed, it was built on the foundations of Duke Humphrey’s Tower to save on costs – which annoyed Flamsteed no end, as the tower’s position was thirteen degrees off true north. The final cost was £520, just £20 over budget, working out at around £80,000 today. The observatory took just one year to complete, and was the very first purpose-built scientific research facility in Britain.

In 1720 Sir Edmond Halley – he of the comet fame – became the second Astronomer Royal at the observatory, following the retirement of John Flamsteed. Three decades later in the 1750s, Halley’s successor James Bradley charted sixty-thousand stars so accurately that his catalogues were still in use as late as the 1940s. The longitudinal problem was finally solved in 1773 by an obscure Yorkshire clockmaker named John Harrison; his first four marine chronometer prototypes, H1 to H4, are on display at the observatory’s museum.

In 1833 a five-foot diameter red time ball was installed on the roof of the observatory: at 12:55 the ball begins rising to the top of the pole, reaching the summit at 12:58; at 13:00 it then makes a sudden drop. Being atop a hill in Greenwich Park, the ball was in view of the Thames, and so allowed mariners, clock makers, and the general public to accurately record the time and set their watches accordingly.

Without a doubt though the main attraction at the observatory is the Prime Meridian: the metal strip that marks the dividing line between the eastern and western hemispheres; since 1999 a green laser has also shone from the observatory along the Meridian across the north London night sky. Running through the line of Airy’s Transit Circle, which was installed by Astronomer Royal Sir George Biddell Airy in 1850, the Greenwich Meridian was adopted as the world’s Prime Meridian at the 1884 International Meridian Conference in Washington, DC (and you thought your work conferences were dull) – although the French, being French, opted not to adopt the standard until 1911; even then they would not use the name "Greenwich Mean Time", instead calling it "Paris mean time, retarded by 9 minutes and 21 seconds". Today the more accurate UTC, or Co-ordinated Universal Time, is used instead, which differs from GMT by up to a second.

In the first half of the twentieth century London was becoming increasingly affected by light and smog pollution, and the electrification of the railways was having a detrimental effect on the accuracy of the observatory’s readings. In 1957 the Royal Observatory was relocated to Herstmonceux Castle, about forty miles south of Greenwich, near Hailsham in East Sussex; it was then relocated again in 1990 to Cambridge, adjacent to the university’s Institute of Astronomy, but was closed just eight years later. In 2018 however the Greenwich site once again became active, with the installation of the £150,000 Annie Maunder Astrographic Telescope (AMAT). Today part of the National Maritime Museum group, the Royal Observatory is a museum and planetarium attracting millions of visitors each year – although I’d suspect most only really want a photo with a foot in each hemisphere.

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