How the Royal Observatory Greenwich Became the Center of Time

The Royal Observatory Greenwich was founded in 1675 by King Charles II and played a crucial role in the development of astronomy and navigation. King Charles II appointed John Flamsteed as the first official government astronomer, known as the “Astronomer Royal,” on March 4 of that year. His instructions were simple: The role of the Astronomer Royal was to study the stars and astronomical movements to calculate longitudes, making navigation safer. Knowing your longitude (an east-west position) and latitude (a north-south position) at sea allowed sailors to know their precise locations, avoid getting blown off course by winds and currents, and map safer routes for fewer shipwrecks.x

The observatory is most famous for defining the Prime Meridian, which divides the Earth into the Eastern and Western Hemispheres, and for establishing Greenwich Mean Time (GMT). As the hub of many scientific measurements and discoveries, Greenwich is one of the finest places in the world to appreciate the history behind navigation, time, and space.

The best way to get to Greenwich is via the Thames Clipper, a boat on the River Thames, where you’ll have some of the finest views of London. It’s a historic route taken by kings and queens, astronomers, and traders for centuries. (It’s also the route by which Henry VIII’s wife Anne Boleyn left Greenwich in 1536 on her way to be executed at the Tower of London.) Today, a section of this waterway and surrounding buildings are a UNESCO World Heritage Site known as Maritime Greenwich.

Maritime Greenwich has an incredible collection of historic sites, including the National Maritime Museum, the Old Royal Naval College, the Cutty Sark (a nearly 200-year old trading ship) moored in the harbor area, and the Royal Observatory. It’s centered in Greenwich Park, where a walkway winds through the trees up the hill to the Royal Observatory — and one of the finest views of downtown London in the area.

Tickets are 24 pounds ($29.50) for adults and 12 pounds ($14.75) for kids. It includes a self-guided audio tour, but extra activities (like planetarium shows) are extra. You can buy your tickets and choose your admission time in advance online.

Sites of the Royal Observatory Greenwich

Flamsteed House

Entering Flamsteed House in the Royal Observatory is like stepping back in time. It’s a unique building equipped with powerful telescopes on the upper levels. It’s where Flamsteed and future successors lived with their families (and was probably the ultimate in 17th-century work-from-home setups).

The Royal Astronomers viewed the stars from the “Octagonal Room” above the living quarters, timing and charting their movements, known as transits. From here, Flamsteed also mapped a “transit quadrant,” which became known as the “Greenwich Meridian.” Eventually this became the Prime Meridian (or Zero Degrees Longitude), and is the point from which all points east and west can be measured.

Over the years, as instruments became more sophisticated, successive Astronomers Royal were able to refine the measurements even more, slightly moving the lines. Then, in 1850, a new telescope known as the Airy Transit Circle (named after the seventh Astronomer Royal, George Biddell Airy) was designed for the Royal Observatory. The following year, this became the official instrument measuring time zones around the world.

Peter Harrison Planetarium

 

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A visit to the Royal Observatory wouldn’t be complete without a look at the stars in the adjacent Peter Harrison Planetarium. Led by expert astronomers, the shows provide excellent insights into planetary activities in one of the world’s most famous scientific centers. Multiple shows run every week on themes ranging from exploring the solar system to kids shows, Chinese Astronomy, astronomy and Islam, and special shows in foreign languages and for people with ASD and other sensitivities. Tickets are 12 pounds for adults and 6 pounds for children, or about $14 and $17, respectively.

The official Prime Meridian

Today, visitors to the Royal Observatory Greenwich can stand on the Prime Meridian, with one foot in the East and one in the West – literally. The Prime Meridian divides the Western and Eastern hemispheres and is the epicenter of the UTC (Coordinated Universal Time) time standard. It’s the single consistent reference point used for setting every other time zone (but is not a time zone in itself) and is used by global and international industries. The aviation sector relies on it for precise flight schedules and air traffic control, finance agencies use for global timestamps, and scientists working around the world use it to ensure observations and measurements are recorded with precise accuracy.

Nearby is the first-ever clock to show the official Greenwich mean time to the public, still standing at the Shepherd Gate entrance near the Prime Meridian line. The next time you have to set your watch for traveling, remember that the origins of why that is begin right here.

The Royal Observatory itself

 

 

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There’s more to see inside the Royal Observatory in Greenwich, including the Great Equatorial Telescope. It’s the world’s eight-largest telescope, still used for astrophotography and mapping double stars (stars that are so close together, they appear to be one). Housed in an onion-domed building, it’s a highlight of any visit to the Royal Observatory. The telescope is rotational and aligned to the earth’s axis, moving parallel to the equator.

Also within the Royal Observatory are fascinating displays of astronomical and navigational interest, including early chronometers used to measure longitude at sea during the 18th century. The famous clocks enabled sailors to both calculate longitude and know the time at sea, preventing marine marine accidents and making trade and commerce safer and more robust.

But it’s not the only innovation developed by Royal Astronomers. In 1767, Astronomer Royal Nevil Maskeline developed a Nautical Almanac. Using the Nautical Almanac involved some mathematical calculations, but was generally less complex than maintaining and operating a highly precise chronometer. Each year, this book of astronomical data was updated by astronomers across the globe, all sending information to Greenwich. It became a critically important tool for navigators around the world, and without it, we may not have the cultural exchanges, knowledge, and bonds the world has today.

There are also changing exhibitions, ranging from displays on pirates and astronauts to deep space phenomenon, night sky photography, naval fashion, and more.

The National Maritime Museum

The National Maritime Museum is also in Greenwich Park and has several highly professional and extremely fascinating displays relating to navigation and time. You’ll find exhibits on historical polar exploration, maritime instruments, and clever artifacts relating to astronomical photography. Displays reflect the genius and creativity of the astronomers who worked in Greenwich and across the globe to further science by observing the stars.

The Old Royal Naval College

The Old Royal Naval College dates from 1660 and is rich in history. It was originally planned as a palace for King Charles II, but instead became a hospital for mariners before becoming a Navy college. One of the highlights is the Painted Hall, completed in 1726 to commemorate the “Glorious Revolution:” the accession of King William III and Queen Mary in 1683. The entire ceiling celebrates Britain’s power as a maritime nation and is one of the most important pieces of art from the 18th century,  occasionally referred to as “Britain’s Sistine Chapel.”

If you visit, note one corner of the ceiling on which artist James Thornhill painted his friend John Flamsteed predicting a total solar eclipse that fell on April 22, 1715. In his lifetime, Flamsteed correctly mapped more than 3,000 stars, and an atlas he wrote was published posthumously by Thornhill. Also in the painting are references to Nicholas Copernicus and his contribution to science and astronomy.

The Greenwich Royal Observatory celebrates 350 years in 2025

The Royal Observatory will celebrate 350 years in 2025 and is holding several special events, including specialist talks and exhibitions. Organizers are planning special shows throughout the year depicting what the night sky looked like in 1675, as well as presentations on the history and founding of London’s only observatory.

Though the anniversary will be celebrated all year, there are three specific dates that are especially important: March 4, when Flamsteed became the first Astronomer Royal; June 22, when the observatory was formally created; and August 10, when the first stone of the observatory was put in place.

More details are available here and will be added throughout the year.