Photo 1: Flamsteed House, the original Royal Astronomer's home office! The red ball drops each day at exactly 1:00 PM
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Photo 2: Schoolkids straddling the Greenwich Meridian (00º 00" 00') |
Photo 1: Flamsteed House, the original Royal Astronomer's home office! The red ball drops each day at exactly 1:00 PM |
On Saturday morning we took the bus
out to Greenwich to visit the Old Royal Observatory. The Royal Observatory has been moved
away from London and this original site has been turned into a fascinating museum. Also on
the same grounds (at the bottom of the hill) is the Royal Naval Museum.
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 Photo 3 The Old Royal Observatory. My red line marks the Greenwich Meridian. |
This is the site of the Longitude
Zero (Greenwich Meridian) line from which the rest of our planet is measured. They have
the Greenwich Meridian line marked with a recessed light strip in the pavement for the
benefit of us tourists so we can have our souvenir photos straddling this reference
East/West line. See Photo 2 for an example! I have marked the Meridian on photo 3 (at
left).
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 Photo 4: The Transit Room. Until 1850, the Greenwich Meridian was defined as centerline of the telescope at right . |
The Greenwich Meridian was set to
coincide with the centerline of the longitude mounted telescope which was used by the
Royal Astronomer to map the star locations for the navigation tables. While the Europeans
were debating whether Greenwich or Paris should have the honor of Longitude Zero, the US
Congress effectively made it a global standard by choosing to establish the four American
continental time zones based on the Greenwich Meridian. I found the museum fascinating, with original (or reproduction) astronomical instruments, and an exhibit of time pieces from hourglasses through to the Hewlett Packard Rubidium standard and Global Positioning Receivers. The featured exhibits are the four Harrison clocks, H1 through H4, the timepieces built to win the "Longitude Prize" offered by the British Government. This was to be awarded to the person who could come up with a way to determine the longitude position on the open seas. H3 and H4 are shown below in Photos 6 and 7. |
 Photo 5: The Harrison Gallery. H1 through H4 are on display along with other important chronometers and timekeeping artifacts. |
Of course the latitude could be easily measured by observing the North Star (or the Southern Cross), but since the earth rotates, there was no way to reliably determine longitude. The obvious solution was to develop a reliable clock which could be used on a pitching ship. By knowing the time of day (or night!) and with the star tables produced by the Royal Astronomer at Greenwich, you could calculate your latitude and avoid sailing into the shore (or the rocks!) |
 Photo 6: Harrison's H3 timepiece |
 Photo 7: Harrison's final, H4, pocket watch. It was made to check H3, but turned out to be more accurate! |