by Harry Lacey

Created on: March 07, 2009

The International Date Line (IDL) is an invisible marker that runs along the meridian of 180 degrees longitude and signals the point at which the date changes. If you are travelling east and cross the IDL, you will lose a day, and if you are travelling west you will gain a day.

The date line first began to find significance around the time that explorers first began to cross the oceans. Magellan, who travelled from east to west, first noticed the change when he and his crew made port at a Spanish enclave on the other side of the line. Upon conferring with those on shore, he discovered that they were certain that it was a different day than that which the ship's logs suggested.

It has been said that the date line received its first mention in a fourteenth-century Jewish Talmudic text, which spoke of differences in time in relation to the position of Jerusalem. To this day, the date line makes it difficult for followers of all religions to judge when they should be celebrating holy days or practising a day of rest if they are travelling over it.

But the International Date Line has always been open to a certain degree of alteration. Historically, it has been moved in order to make trade easier for countries with close ties. Samoa, for example, changed its position to being three hours behind California in 1892 in order to make for a better trading environment. As territories have changed hands, so the International Date Line has moved. When Alaska was purchased by the United States in 1867, the date line was moved to accommodate the territory's switch to American time and Alaska lost a day.These switches have been allowed to take place because the line has never been formalised in any kind of international agreement. It is a completely artificial construct that exists only on maps, and countries have the right to alter their standing in regards to the line's position.

The position of the International Date Line has long raised such interesting divisions. For example, flying between Fiji and Samoa, islands in the Pacific in relatively close proximity to each other, means travellers have to lose a day, and technically arrive the day before they left. Further north, the twin Diomede Islands in the Bering Strait are just 4km from each other, yet are separated temporally by 21 hours.Visitors to Little Diomede, which is American, have the bizarre experience of being able to gaze across the water at Russian Big Diomede and effectively 'look into the future'.

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