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.

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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.

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Longitude, Harrison Clocks, Lunars and Captain Cook (Part 2)

(Continued from Part 1)

Lunars

During these same years, another competing method had been developed for finding longitude using the moon and stars themselves as a clock to determine the time back in Greenwich, England. This was the method of lunar distances or lunars. The moon moves the distance of its own diameter in about one hour, a distance called a ‘lunar’.

In a sense, the moon’s movement is similar to that of a clock handle amidst the stars, and calculations based on the moon’s movements across the background of the stars at any location in the world (providing conditions were right to view the moon) could be used to determine the time back in good old Greenwich, England.

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