Latitude and Longitude

The travellers of the ancient world positioned themselves using landmarks and simple maps. This worked well locally, but different methods were needed for travelling further afield across featureless terrain such as sea or desert. Travellers now required a frame of reference, or co-ordinates, to fix their position. In the 3rd century BCE, the Greeks, most notably, Eratosthenes of Cyrene, accurately calculated the Earth’s circumference based on shadow angles cast by the sun. This provided a foundation for understanding latitude. Longitude, the angular distance east or west of a prime meridian, was a more challenging problem due to the Earth’s rotation. Accurate measurement required precise timekeeping. The development of longitude is often associated with the quest for determining a ship’s position at sea to prevent navigational errors. In the 16th and 17th centuries, advancements were made by navigators and astronomers. The Dutch inventor Gemma Frisius proposed the idea of using a clock to determine longitude based on time differences between a ship’s location and a reference point. In 1714 the British parliament offered a £20,000 prize to any person who could determine longitude a sea. An amateur clockmaker from Yorkshire, England, named John Harrison, eventually solved the problem with his marine chronometer, (H4), which allowed mariners to accurately establish the time difference between their own location and the Greenwich meridian (0°), and thereby calculate their degree of longitude. Today it’s all done electronically with Global positioning Systems, GPS.