This was followed in 1598 by a similar challenge from Philip III, to whom Galileo wrote, telling him that eclipses of Jupiter’s moons would reveal the secret. In 1567, Philip II of Spain offered a prize to any person who could provide a solution to the problem. Unfortunately, sufficiently accurate clocks weren’t going to be available for another 230 years or so, but when they were, the method Frisius used was shown to work.Ĭracking longitude was not only important for the safety of navigators, but vital for the development of sea-borne trade. The clock would be set on departure and kept at absolute time, which could be compared with the local time on arrival. In 1530, Gemma Frisius proposed a new method of calculating longitude using a clock.

However, his method required an accurate clock, something yet to be invented. He further suggested that absolute time be determined by observing lunar eclipses, measuring the time when a lunar eclipse started and finished, and finding the difference between this absolute time and local time. He proposed a zero meridian passing through Rhodes. Hipparchus, a Greek astronomer (190–120 BC), was the first to specify location using latitude and longitude as co-ordinates. Great minds had tried for centuries to develop a method of determining longitude. To determine your exact location you also need to measure your line of longitude. The first instruments used at sea to measure latitude were the quadrant and the astrolabe, both of which had been used for years by astronomers to measure the inclination of stars.īut knowing your latitude wasn’t enough. Over the centuries, increasingly sophisticated devices, like the gnomon and the Arabian Kamel were designed, to measure the height of the sun and stars above the horizon and thereby measure latitude.

Latitudeīoth the Phoenicians (600 BC) and the Polynesians (400 AD) used the heavens to calculate latitude. Travellers now required a frame of reference, or co-ordinates, to fix their position. This worked well locally, but different methods were needed for travelling further afield across featureless terrain such as sea or desert. In ancient times, people positioned themselves using landmarks and rudimentary maps.

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World map with latitude and longitude