In Greenwich we visited the Royal Observatory, home of Greenwich Mean Time (GMT). You can see the telescope dome to the left, and the red time ball that drops at 1:00 PM each day. Major studies by the astromomers and the development of accurate clocks enabled the establishment of the longitudinal navigational lines around earth. The lines start here, at the Prime Meridian, where Sallie is standing with one foot in each hemisphere. 
By an international agreement of 1864, this is the official starting point for every new day, month and year.
The Observatory was founded by King Charles II in 1675, and the building designed by Christopher Wren. The main purpose was to improve navigation. In 1714, the British Government offered a prize of 20,000 pounds (a fortune for those days) to anyone who could come up with a solution to provide longitude to ships at sea. Because there was no way for ships to figure out where they were at sea, the nation had experienced many shipwrecks with devastating losses.
The eventual winner of the prize was John Harrison, who designed a marine chronometer that worked. We visited the Time Galleries, which feature the winning one and other tries by him and others. There are other historic timepieces and interactive explorations of time in our lives.
This is part of the reconstruction of the home of the first Royal Astronomer, John Flamstead, which was a part of the Royal Observatory. Although made a member of "The Royal Household", Mr Flamstead received only 100 pounds a year for his work and that of his wife, who served as his assistant. When he died, his wife — not so surprisingly — sold most of his belongings.
Here is a good website for more information about the Observatory and its museums: http://www.rog.nmm.ac.uk
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