This article is part of FT Globetrotter’s guide to London
To a navigator, time and distance are tightly linked. Earth turns 360 degrees on its axis every 24 hours. This means that a person standing on the equator travels east one degree of longitude, approximately 111km, every four minutes. People have long realised that the passage of the sun, stars and other bodies across the sky caused by rotation represented — with careful observation and some neat calculations — a reliable method both for timekeeping and determining a location on Earth’s surface.
Encouraged by my father-in-law, who was an air force navigator, I learnt how to navigate in 1999 as part of a long-held dream to train for my private pilot’s licence. Ever since, I’ve been fascinated by the diverse mix of geography, astronomy, mechanics, maths and history at navigation’s heart.
Although today the Royal Observatory Greenwich, in south-east London, is an excellent museum, for almost 300 years the site was a centre for astronomical and navigational observations and research. Its handsome buildings, some of them Grades I- and II-listed and one, Flamsteed House, designed by Sir Christopher Wren, sit on top of a hill in Greenwich Park commanding beautiful unobstructed views of — as well as the night sky — the borough of Greenwich, the Thames, Canary Wharf and, nine kilometres to the west, central London. It owes its very existence to a pressing 17th-century need for research into navigation. King Charles II founded it in 1675 with a brief to find a practical method of fixing longitude for precise navigation, as maritime power was becoming crucial to national success. The walk outlined below gives insight into the history of navigation and timekeeping and the observatory’s pivotal role in it.
Meridian Observatory
A good place to begin is the Meridian Observatory, a collection of rooms built between the 17th and 19th centuries to house instruments, with large windows and opening roofs to observe the sky along meridians — imaginary lines on Earth’s surface linking the north and south poles.
Some of the beautiful instruments on display are aligned as they originally were with meridians bearing the names of the Astronomers Royal who established them: Flamsteed (1689), Halley (1725), Bradley (1750) and Airy (1851). They used telescopes to plot positions of celestial bodies in the sky in much the same way that towns are plotted on maps of Earth’s surface. The mural quadrant consisting of a telescope mounted on a metal quarter circle that gives the device its name and the telescope installed on Bradley’s meridian are delightful examples of 18th-century scientific instruments but the most impressive is the 1851 Airy Transit Circle, the device responsible for both the adoption of the Greenwich meridian becoming Earth’s prime meridian and Greenwich mean time as a global time standard
Its telescope’s observations were precisely observed by microscopes in the transit’s supporting blocks, plus they were timed by a reliable clock. Before the 1884 International Meridian Conference, there was no agreed world prime meridian — a reference line of zero degrees longitude — with many countries and organisations using a variety of meridians for the purpose. The conference resolved that the meridian running through the Airy Transit should become Earth’s prime meridian from then on. As the meridian was at Greenwich, GMT simultaneously became a world-standard time reference. However, in 1988, the IERS (International Earth Rotation Service) meridian, based on a new set of coordinates calculated from satellite data, came into operation. Differences in the methods for fixing satellites’ and the transit circle’s positions mean the IERS meridian is actually 102.5 metres east of Airy’s, although it is still based on his prime meridian. You can demonstrate this, and impress your friends, by placing a smartphone with a mapping app on the prime meridian and you’ll note that the longitude given is not exactly zero.
Flamsteed House
You then cross the observatory courtyard — pausing, as every visitor does, to stand on the prime meridian with a foot in the east and west hemispheres — and enter Flamsteed House, the museum’s oldest building. It’s an eminently practical design. The ground floor contains the former living quarters for the Astronomers Royal, 10 of whom lived there over almost 300 years until 1948. Its rooms give an insight into their lives, with objects such as an ostentatious inkstand presented to George Airy for advising the City of Chester on the heights of tides for navigation on the River Dee to delightful scientific teaching aids to inform the astronomers’ children.
Above the living quarters is the Octagon Room, a rare chance to see an original Christopher Wren-designed interior. Large windows designed to give unobstructed views of the sky and, unintentionally, the local area, make for a sublime, bright space, and tall ceilings permitted the fitting of the long pendulums necessary for the accuracy of the room’s clocks. Beautiful though it is, the room is flawed. As a cost-saving measure, it was built on the previous building’s foundations, meaning it was not aligned with a meridian, making it frustratingly impractical for observations.
Back on the ground floor, another gallery explains the observatory’s role in the longitude problem, finding a reliable and practical way of pinpointing an east-west location at sea to enable safe and efficient maritime travel. Two rival theories competed to solve it, one involving observation of celestial bodies and the other reliant on the accurate keeping of time at sea. Both had their proponents, advantages and drawbacks.
Personally, my highlight of this gallery, and indeed the museum, are the clocks of John Harrison (1693–1776), one of my heroes. Harrison was a skilled and extremely determined clockmaker who devoted years to solving longitude with his amazing timepieces in pursuit of the fortune offered by the British government’s Longitude Prize, which he eventually won. The four mechanisms on display are as ingenious as they are beautiful, compensating for all the bad things a dangerous 18th-century ocean voyage could throw at them.
Another floor down is the Time and Greenwich Gallery, where the exhibits illustrate modern timekeeping and the role the observatory has played in creating increasingly accurate timepieces. The pursuit of accuracy is key here, and the intriguing timepieces on show illustrate how the regular swing of pendulum clocks was superseded by electronic and other devices. One clock’s signals were transmitted by telegraph to provide GMT for Britain’s railways, creating standard time across the country and replacing the chaotic 19th-century system whereby every town set its clocks by the noonday sun – for example, pre-GMT, clocks in Bristol were 10 minutes behind those in London. Another clock on display was the source from 1924 to 1949 of time signals used by the BBC as the basis of its hourly “six pips” broadcasts.
Amazing clocks based on the frequencies of components of atoms (1949) and later on GPS signals from satellites in space (1993) brought further accuracy. Quantum clocks in development now will eventually gauge their accuracy in spans of billions of years.
Time & Society Gallery and the Great Equatorial Telescope
Heading back across the courtyard, above the Meridian Observatory is the Time and Society Gallery. Civilisation runs on accurate timekeeping, and exhibits here chronicle the inventions that achieved it: devices that took advantage of celestial movements such as exquisite sundials, astrolabes and quadrants; mechanical clocks with intricate escapements and pendulums; and modern electronic and GPS timekeepers. One is reminded how crucial timing is, whether it’s in a London Transport time recorder, a second world war “zigzag” clock used to make ships vary their course to evade enemy attacks or a Russian clock for timing moves in chess matches.
Progressing up a spiral staircase takes you to the 1893 Great Equatorial Telescope, housed in the onion dome that makes the observatory a distinctive landmark on Greenwich’s skyline. It’s the largest refracting telescope in the UK and still in use by the museum for public astronomy sessions. On initial viewing, it appears to be aligned at a puzzlingly odd angle but this alignment means the telescope moves parallel to the equator so that stars can be easily tracked across the sky as they slowly progress. The telescope’s mounting in a frame originally designed for a narrower instrument adds to its quirky appearance. Looks are deceptive, though, and the telescope’s precise observations were instrumental in calculating the masses of double stars that rotate around each other.
When time’s up, don’t forget to check your watch on the 1852 Shepherd Gate Clock as you leave. The first public clock to display Greenwich Mean Time (albeit with a 24-hour face), it is still highly accurate and a last reminder of the importance of Greenwich in helping us know our time and place.
Have you visited London’s Royal Observatory Greenwich? Tell us in the comments below. And follow FT Globetrotter on Instagram at @FTGlobetrotter
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