Royal Observatory greenwich magnetic clock

Last Updated on August 16, 2019 by Michael

For geography geeks a visit to the Royal Observatory in Greenwich is a must. Located just down the Thames from central London, it’s the home of both the Prime Meridian (zero degrees longitude) and Greenwich Mean Time; the time upon which all others are based. A popular activity for visitors is standing with one foot on either side of the Prime Meridian so they are in both the Western and Eastern Hemispheres.  But there’s more: London’s only planetarium, a free astronomy museum and the adjacent National Maritime Museum that’s also free.

Royal Observatory Astronomy centre

At the Astronomy Centre you can touch a prehistoric meteorite from Namibia.

With a web site named “Changes In Longitude” naturally we had to visit the Prime Meridian. While some of the sites at the Royal Observatory are free, entrance to the Prime Meridian costs 7 pounds ($11). For this fee the visitor can also enter Flamsteed House to see where the Astronomers Royal lived and worked along with the Octagon Room, a wonderfully decorated observatory where some of the telescopes can still be used.

Royal Observatory Octagon room

The Octagon Room is a one of the few surviving interiors designed by Sir Christopher Wren.

The room, designed by Sir Christopher Wren, was supposed to be used to calculate the earth’s position but since none of the windows lined up with a meridian, ironic given its location, measurements had to be taken from a small shed on the grounds. No one dared bring this little problem up with King Charles II who funded the Observatory.

One of the most popular exhibits is the bronze line embedded in the courtyard that signifies the Prime Meridian of the world: Longitude 0˚ 0’ 0’’. Visitors line up to have their picture taken as they straddle the line and proclaim themselves “king of the world.” Names of major cities around the globe are carved in stone to show their relative longitudes.

Royal Observatory Greenwich Prime Meridian Line Visit

Straddling the world at longitude zero.

The museum’s exhibits highlight the discovery of longitude by a self-taught inventor named John Harrison in the 18th century. Before he came along, ships could view the stars to calculate their latitude, but had no reliable means of gauging their longitude. This lack of knowledge about their relative position led to ships crashing onto the rocks of western England as they returned home.

Harrison’s invention was an ingenious clock that could accurately keep time at sea, a requirement for calculating longitude. His actual clocks are on display in the museum and highlight the thought process leading up to the breakthrough H4, a timepiece that was every bit as revolutionary in its day as an iPad is today.

Royal Observatory Greenwich Harrison H4 timepiece

This unassuming device solved the problem of longitude and saved thousands of lives.

For even more about the discovery of longitude, read the captivating book: Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time by Dava Sobel.

A visit to Royal Observatory Greenwich is a highlight for travelers interested in many subjects from geography to seafaring to outer space. But just wait until the Olympics are over, it’s closed until August 4th because equestrian events are taking place on the grounds.

Visitor’s Information

For visitor’s information click the Royal Observatory web site.

Click the link to Amazon to learn more about the book Longitude.

Prime Meridian line Greenwich

Even Little Rocky couldn't resist hamming it up at the Prime Meridian.