The Royal Observatory in Greenwich started life in 1675 as a scientific research institute dedicated to solving the problem of the measurement of longitude.
Britain was a seafaring nation and it was vitally important that ships navigating the ocean were able to calculate their position at sea. Accurate star charts and later, very accurate clocks that could stand up to the rigours of ship board life were a major part of the research carried out at the observatory.
Longitude is a measure of how far around the globe a place is located. In 1884, an international conference agreed to measure longitude from a fixed point, termed the Prime Meridian, located at Greenwich. This meridian is marked at Greenwich with a stainless steel strip.
Due to modern, scientific mapping techniques, there are a number of prime meridians in the area which differ from the original meridian by up to a few metres.
Longitude can be measured by taking the angle of the sun whilst knowing the time of day. Hence Greenwich was and still is the home of global timekeeping.
The observatory is located at the top of a hill in Greenwich Park above the National Maritime Museum. It offers stunning views down to the museum and across the river to Canary Wharf and Docklands.
The image above shows a laser beam marking the zero longitude or Prime Meridian.
Details: Visit Greenwich Observatory