A brief introduction to

Saving Lives with Clocks and Telescopes

Louise Devoy, Curator, tells us why Royal Museums Greenwich have nominated the Royal Observatory as one of 100 buildings and places that tell England's Story.

From the physics lab in Manchester where the atom was first split, to the hut in Gloucestershire where Edward Jenner developed the first vaccine. England’s historic places are a hotbed of innovation. 

Royal Museums Greenwich has nominated the Royal Observatory, Greenwich as one of the 100 Places that tell England’s story. Louise Devoy, Curator of the Royal Observatory, tells us about the stratospheric impact of this place.

Today we rely on our mobile phones to tell us where we are and what time it is but it’s easy to forget the complex scientific and technological principles that underpin these numbers.

As Britain’s first state-funded scientific institution, the Royal Observatory played a vital role in both timekeeping and navigation for nearly three centuries. It’s an essential and irreplaceable part of our history with a variety of interesting characters and innovative technology, all set within a beautiful English park near the River Thames in Greenwich.

Royal Observatory Greenwich from Crooms Hill, English School BHC1812
A view of the newly-constructed Royal Observatory, about 1696. National Maritime Museum | BHC1812

It all started with a rumour that began to circulate around the English court during late 1674 when sources claimed that French astronomers had improved a means of navigating by the Moon and stars. With new trade routes opening up towards Asia, Africa and the Americas, European governments were keen to improve navigation at sea that could save lives and enhance profits on increasingly lucrative commodities such as coffee, tea, spices, textiles and timber.

Oval miniature of Charles II by Samuel Cooper, around 1660-65.  National Maritime Museum | C9422

As a consequence of these rumours, King Charles II was persuaded to set up an observatory and the first Astronomer Royal, John Flamsteed (1646–1719), started work in Christopher Wren’s elegantly-designed new observatory in 1676. For the next forty years, Flamsteed diligently observed the stars, plotting their position according to the time at which they crossed a meridian (north-south) line. He also devised Greenwich Mean Time (GMT): Flamsteed realised that the Sun did not cross the meridian line at exactly the same time each day when compared against the steady beat of a pendulum clock. To compensate for this, he created an average (mean) time that evened out the difference between solar time and clock time, as measured by an observer at Greenwich.

Astronomers at work in the Octagon Room, around 1712. National Maritime Museum | L8089

Sadly, Flamsteed died before his work was published but the quest to improve navigation at sea continued to occupy successive generations of Astronomers Royal. In particular, the fifth Astronomer Royal, Nevil Maskelyne (1732–1811), created the annual publication of astronomical data known as the Nautical Almanac, an essential guide for every navigator at sea that continues to be published today by the UK Hydrographic Office. Maskelyne and his assistants carefully observed and measured the stars each clear night, sending out parcels of data to a network of mathematicians across the country who number-crunched the observations into a useable format.

Meanwhile, the Longitude Act of 1714 inspired a range of scholars and inventors to try and devise a means of determining longitude (your east-west position) at sea, enticed by the chance to win a reward of £20,000 (equivalent to several million pounds today). After many designs and trials, the carpenter and clockmaker John Harrison eventually received the reward by the early 1770s for his innovative marine timekeeper, known as H4. By comparing their local time (measured by the Sun) to the time back home (maintained by the marine timekeeper), mariners could convert their time difference into a measure of longitude. Given that the Earth rotates once on its axis (360°) each day (24 hours), one hour’s time-difference is equivalent to a longitude difference of 15 degrees (360°/24). Simple in theory but highly difficult to measure in practice!

John Harrison’s successful design, known as H4. National Maritime Museum | F7024-001

Over the next few decades, craftsmen adapted Harrison’s design to create the marine chronometer which became an essential piece of kit for every navigator. By observing the dropping of the Observatory’s roof-top time ball at 1pm each day, navigators on the River Thames could check their chronometers before heading out to sea. In addition, chronometers issued to Royal Navy ships were sent to the Royal Observatory between voyages to be tested and reassessed.

The time ball, first installed on the roof of Flamsteed House in 183
The time ball, first installed on the roof of Flamsteed House in 1833. National Maritime Museum | F6073-027

Meanwhile, the rapid expansion of the railway network across Britain during the 1840s meant that Observatory time was important for more than just navigators at sea. For centuries, people had relied on sundials and clocks set to local time to help structure their day. This was impossible to use for long distance rail journeys when the time difference between cities could vary by 30 minutes or more. The railway companies all agreed to coordinate and use Greenwich Mean Time, relying on a series of electric signals distributed from the Observatory via the telegraph network.

The galvanic master clock with slave dials, made by Charles Shepherd in 1852
The galvanic master clock with slave dials, made by Charles Shepherd in 1852. National Maritime Museum | D9280

Finally, in October 1884, delegates at an international conference in Washington DC decided to recommend that all governments should adopt the meridian defined by the Observatory’s Airy Transit Circle instrument as the prime meridian (zero degrees longitude), from which all locations on Earth could be defined. Discussions at this conference also sparked the creation of the international system of time zones which we continue to use today.

The instrument used to define the historic prime meridian of the world, the Airy Transit Circle
The instrument used to define the historic prime meridian of the world, the Airy Transit Circle. National Maritime Museum | L2156-003

So, after our whirlwind tour across three centuries of hard work and innovation, we can clearly see that the Royal Observatory is not just an irreplaceable part of British history but an essential part of our interconnected global history that we still rely on today!


Find out more about visiting Royal Museums Greenwich, including the Royal Observatory here.


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There’s a tree by a house in Lincolnshire where Isaac Newton once stood, and an apple fell and lit up the future.

There’s a house in Stratford where the greatest playwright that ever lived was born. There’s a bridge in Bristol where the world’s first bungee jump took place

England’s historic places bring our extraordinary history to life. We need you to nominate the historic site you think is most important to our national story, and help to tell a history of England in 100 places.


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Irreplaceable: A History of England in 100 Places is sponsored by specialist insurer, Ecclesiastical.

Header Image: Postcard Image of the Royal Observatory, Greenwich. © Historic England Archive PC09838 

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