Royal Observatory, Greenwich

Engineering places: Royal Observatory, Greenwich

Image credit: Jessica Blanc | Dreamstime

In celebration of IET@150, we look at feats of engineering from around the world.

In the 17th century, it was not the ‘done’ thing to call yourself an engineer. The word had connotations of lowly craft, yet in the Age of Enlightenment there were engineers everywhere, simply known by other names, and not least on a small hill deep in the countryside to the east of London.

That hill was of interest to perhaps the period’s greatest engineer, Sir Christopher Wren. He was part of a commission tasked with creating a Royal Observatory. Wren had handily been Professor of Astronomy at Oxford, and his commission recommended the building of England’s first state-funded scientific institution in the clear country air of Greenwich. Charles II clearly liked the plan and called for immediate action, appointing the first ‘King’s Astronomical Observator’ (later Astronomer Royal) the same day.

John Flamsteed’s job was to use the stars to help navigate on Earth. What he needed now was a building and some serious engineering to measure the heavens. Fortunately, Wren also had something of a reputation as an architect and so was given the job of building Flamsteed House on the site, whose foundation stone was laid on 10 August 1675. Just a year later, Flamsteed was delighted to be at the helm of England’s greatest scientific institution. He was less delighted to discover that Wren had built his observatory on an extant foundation and his observatory was 13 degrees off true north.

Flamsteed and his successors had a lot on their plate. When he began, the best star catalogues charted a mere 100 stars. His job would be to fill in the gaps.

This should have taken on a greater urgency in July 1714 when, following the wreck of a British fleet off Scilly, the Longitude Act set up a Board of Commissioners, including the Astronomer Royal, to find a more reliable method of determining longitude than the then current soundings and dead reckoning. However, the Board did not meet until 1737 when the development of accurate small marine timepieces began to interest astronomers.

By this point, the observatory had greatly improved the charting of the night sky – the third Astronomer Royal’s 60,000-star catalogue proved so accurate it was still used in the Second World War. Yet this was not enough to measure longitude. What was needed was a way of calculating a reference time at a known point and then a method of recording that time and comparing it to local time.

By the 1760s, John Harrison’s brilliant marine chronometers were overcoming the problem of operating clocks on moving ships. This was no doubt a great relief to the Astronomer Royal who could now return to Greenwich from months at sea, judging the operation of the device. All that remained was to decide on a reference time zone. As the well-travelled Astronomer Royal was also the publisher of the Nautical Almanac, his home and the meridian line that ran through it became the de facto British zero meridian. Over the next century, at least for the British, time would begin here, marked from 1833 by another engineering marvel – the dropping ball, which told ships in the Pool of London that at Greenwich it was exactly noon.

Even then, Greenwich time was not universal, even across Britain, as local time worked perfectly well until the advent of railways, which made differences between towns problematic, particularly for those writing timetables. The answer came again at Greenwich, where clockmaker Charles Shepherd created an electrical clock whose time-pulse could be distributed, ensuring everywhere had the same time. With the advent of radio this electrical pulse system became famous as the ‘pips’.

International time would follow suit in 1884 when a conference in Washington DC agreed the Airy Transit telescope that had sat on the Greenwich meridian since 1851 would become the Prime Meridian for the world and mark the beginning of the Universal Day. The transit telescope itself was disarmingly simple, aligned permanently and exactly on the meridian, from where the crossing of certain ‘clock stars’ could be timed and their elevation measured using micrometre gauges. This beat out the pulse of Universal Time.

During the Second World War, the Observatory and most of its delicate engineering was moved out of London. Post-war, with growing urban light pollution, it was decided to relocate to Herstmonceux Castle in East Sussex. The Greenwich site was re-invented as a museum and the now famous brass meridian line was laid, on which generations of children have now happily planted one foot in the eastern hemisphere and one in the west.

Despite the return of the great 28-inch refractor to Greenwich to celebrate the site’s tricentennial in 1975, the observatory’s real work was moved to still clearer skies in the Canary Islands, and the organisation controlling it moved to Cambridge before being closed completely in 1998. Having conquered time, and in turn ceded the job of measuring time to the infinitesimal vibrations of atomic clocks, it was perhaps no longer seen as necessary.

Yet the Greenwich site lives on and not simply as a museum. Thanks to improvements in filtration, optics and computing, Greenwich Observatory installed its first new telescope in 2018. London’s lights no longer dazzle the observatory and time, in Greenwich, again marches on.

Timeline: The Royal Observatory

1674: King Charles II is persuaded to explore the creation of a royal observatory.

4 March 1675: A Royal Commission recommends the foundation of an observatory. John Flamsteed is named Astronomical Observator.

10 August 1675: The foundation stone for Flamsteed House, the first building on the site, is laid. It is designed by Wren and costs £520, being £20 over budget.

10 July 1676: Flamsteed moves into the observatory.

1680: Flamsteed takes the first magnetic observation.

July 1714: Longitude Act creates Board overseeing efforts to determine longitude reliably.

1750-1762: The third Astronomer Royal, James Bradley, charts 60,000 stars.

1767: Astronomer Royal Nevil Maskelyne begins publication of the Nautical Almanac.

1818: The Royal Observatory is put under Admiralty control and charged with maintaining the Navy’s marine chronometers.

1833: Daily time signals begin with the dropping of a red ball.

1847: Greenwich Mean Time is adopted across Great Britain by the Railway Clearing House.

1851: Airy Transit circle first used.

1884: Greenwich meridian adopted as primary worldwide.

1893: The 28-inch Great Refractor is installed.

1899: The New Physical Observatory is completed.

1924: Greenwich Time Signal first broadcast.

1939: Wartime evacuation; work in Greenwich minimised.

1947: The 28-inch telescope is moved to Herstmonceux.

1957: The scientific work of the observatory moves to Herstmonceux and is called the Royal Greenwich Observatory (RGO). The Greenwich site becomes a museum.

1960: A brass strip marks the prime meridian at Greenwich.

1967: Isaac Newton Telescope inaugurated at Herstmonceux.

1975: 28-inch refractor returns to Greenwich to mark tricentenary.

1979: Isaac Newton telescope moved to Canary Islands.

1990: RGO goes to Cambridge.

1998: The Royal Observatory, Greenwich, becomes part of the National Maritime Museum.

2018: The AMAT telescope is installed at Greenwich.

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