Global Coordinates

Ptolemeus was among the very first to introduce global coordinates, the so-called longitudes and latitudes. This system is still in use today.

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Click for maps showing the definition of longitudes [GIF, 7k] and latitudes [GIF. 6k]

During the last 1000 years, several sailing nations have contributed to the ever increasing knowledge of geography.

Portugal was among the very first countries in which mathematical navigation was taught. These techniques were later refined into extreme details, for instance by the British Navy and their astronomers.

As a result, in particular by the year-long mapping voyages by famous Captain James Cook (1728 - 1799), sailing nations all across the World in 1884 agreed to make Greenwich - the site of the main astronomical observatory in Britain, located near London - the international zero-point on all maps. Thus the longitude of the Greenwich Observatory is exactly 0°.

As a result of this definition, the students on this photo - outside the Greenwich Observatory - are located in two "different" parts of the world - in the Western and the Eastern Hemisphere, respectively.

Exercises:

1. Read about some of the great sailors who travelled to distant countries. Who were Vasco da Gama, Fernando Magellan and James Cook? Which countries did they visit? Which problems did they encounter en route?

2. In the novel "Captain Grant's Children" by Jules Verne, the famous 19th-century French science-fiction writer, a group of sailors catches a huge shark. In its stomach, they discover a message in a bottle.

The letter has been written by Captain Grant - stranded on an uninhabited island. The writing with the Longitude of this island is not readable, but the latitude is mentioned to be approx. 32° South.

Where might Captain Grant's island be located ? Take a globe and discuss the possibilities.