London: Royal Observatory, Greenwich

From the Earl’s Court Underground Tube station, I took the District line to Westminster, then the Jubilee line to London Bridge. From there, I switched to the Southeastern Rail Line and arrived at the Greenwich Rail Station about 45 minutes after I had left my hotel.


Earl’s Court Underground Tube Station, London.

A twenty-minute walk to the top of a large grassy hill brought me to the Royal Observatory, Greenwich, which overlooks London and the River Thames and is a famed location in the history of astronomy and navigation. It is a spring day in London, and today the green park expanse below the observatory is filled with both tourists and locals enjoying the sunshine.


The view from near the observatory.

On this day, streamers of white cloud dance across blue skies where years ago on countless nights noted astronomers had made their celestial observations.

The Royal Observatory was commissioned by King Charles II in 1675 and built shortly thereafter. John Flamsteed was appointed the first Astronomer Royal, and the building that occupies the site is often called Flamsteed House after its first occupant. The old observatory and buildings are no longer used for scientific research, but rather have been turned into a historical museum.


Royal Observatory, Greenwich.

But during its day, along with providing an elevated spot for celestial observations, the Royal Observatory, Greenwich also served as a reference site for both time and location, both of which are still used today.

The Prime Meridian, the arbitrary starting point for all lines of longitude that circle the earth, was designated to be located here in Greenwich.


From this starting point, lines of longitude are termed to extend 180 degrees around the earth both toward the east and toward the west. In the courtyard of the Flamsteed House, a stainless steel strip marks the Prime Meridian line. Gaggles of tourists straddle the line and take photos.


The Prime Meridian – it all starts from here.

But, actually,  because of changes in the way the Prime Meridian is measured (modern geodetic reference systems), the true Prime Meridian is actually located about 100 meters distant from the line in the courtyard. Here is a photo of my handheld GPS receiver at the true Prime Meridian showing a longitude of 00 degrees 00.000′.

00 00.000

Second number on my GPS receiver’s screen shows that I am at longitude 000 degrees 00.000′!

The Royal Observatory, Greenwich also served as a reference center for time. Originally termed Greenwich Mean Time (GMT), the time as initially determined by celestial observations here at the observatory, and kept on the most accurate clocks of the day, served as the reference time for time all around the world. Any given location on the earth could be said to be so-many hours, minutes, and seconds earlier or later than the time in Greenwich, England. This reference time is still used, although it is currently termed Universal Time (UT).

These two factors, longitude and time, intersected in perhaps what was the heyday of the Royal Observatory. As England expanded its empire over the seas, countless ships were lost due to the inability to accurately measure longitude, that is, to accurately determine on which vertical line that circles the earth a ship was at a given time. Nightly celestial observations and recordings for years by such notable Royal Astronomers as John Flamsteed, Edmond Halley (of Halley’s Comet fame), Nevil Maskelyne, and others attempted to find patterns in the stars, the moon, the planets and planets’ moons to solve this problem and to enable ships to accurately and consistently determine their position at sea. The problem was in great part solved by John Harrison, who over a number of years created timekeepers (clocks) that could accurately preserve the time at Greenwich while carried at sea over long distances and long periods of time.

By knowing the time in Greenwich, England and comparing it to the time at your present location using the sun, one can determine one’s longitude anywhere on the earth’s surface (see my previous blog post on the Harrison clocks).

Harrison’s clocks—there are four of them—are on display in the Flamsteed House. All are intricately designed and still operating. The first three are quite large. The final Harrison clock, termed H4, looks like a very large watch about six-inches in diameter, and for this, Harrison was awarded the Board of Latitude award, a monetary prize for the individual who solved the vexing problem of determining longitude.

After spending a long period of time in the museum, and—yes—after having my picture taken straddling the Prime Meridian line with all the other tourists, and after sitting on the hilltop in the sunshine overlooking London, I made my way back toward my hotel, pleased that I had visited the Royal Observatory, Greenwich, truly a fascinating place where history and science intersect in a beautiful location.



All photos by the author.



2 thoughts on “London: Royal Observatory, Greenwich

  1. I’m not up on exact time, nor exact location, but … of my favorite puzzlements ( which I actually came across in the Bible ) concerns longitude and latitude…..namely, how, when going north or south, at some point you stop going south and start going north ( and visa verse ) …..BUT when going east, you just keep going east and when going west you just keep going west without end ….. that utterly fascinates me….I know it’s got something to do wth the magnetic pole but I don’t REALLY get it .

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