Traveling across the dateline

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LONDON, England (CNN) -- Los Angeles International airport is becoming ever more important as the new gateway into the United States for travelers from Asia. But even frequent flyers who cross the Pacific Ocean often have to ask themselves, "what day is it?" as passing over the international dateline adds to the confusion felt by jet-lagged travelers.

The Royal Observatory in Greenwich, London, is the self-styled home of time as it the site of zero degrees longitude. There was international agreement in 1884 that it would be the first point of measurement, but no one decided where each day stopped. As a result the mystery of the international dateline was born.

"If you look at the date line as it passes through the Pacific it is not a straight line because there are kinks to move it out of the way of the major land masses," David Rooney, curator of Greenwich Observatory told CNN's Richard Quest.

"And then as you go through the island groups of the Pacific you will see that it has changed over time, that individual groups can choose to move from one day to the next or backwards, usually not for any other reason other than they have got a new relationship with a different country, or with other islands in the Pacific," said Rooney.

There is no official treaty to fix the position of the dateline; politics as much as geography determines its position. Russia and the USA may only be a few miles apart but it was decided to keep them a whole day apart by skewing the path of the line. And the Philippines hopped from one side to the other once their trade routes started to favor the U.S. instead of Europe.

The dateline problem was first noticed in 16th century, when circumnavigators were flummoxed that their impeccably kept ships logs seemed to be a day off on arrival back in Europe.

The rules may be consistent - going east subtract a day, going west add a day. But the dateline is anything but firm. It has changed often, with countries and islands swapping sides. Most recently Kiribass decided to move itself onto one side of the dateline in 1995 and so - briefly - acquired fame as the first place on earth to see the new millennium.

"It's a strange experience but it's not a particularly difficult one.," Rooney told CNN.

"As the Earth rotates and as different times are held in different parts of the world, there is a point where the time is the same but you have to change the day. "

It does throw up some strange anomalies. Take a two hour flight from Tonga to Samoa and you end up arriving the day before you left.

For more about the international dateline watch this month's CNN Business Traveller.

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January 18: 14:30 GMT

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