In 1519, the Portugese explorer, Ferdinand Magellan along with 241 men set out to travel around the Earth. These men kept very careful records as they travelled. Yet, when they returned back, they found that their calendars were off by one day compared with the calendars of everyone in their home countries (Spain and Portugal). What happened? How did these men loose an entire day?
The day was not lost all at once. It was lost little by little, as they traveled around the Earth. Here is the explanation.
If you travel around the world from East to West, you would have to change the time on your watch by one hour for every 15°of longitude crossed, a complete circuit would make you adjust your watch time by 24 hours. This would lead to a difference of one day between the date on your clock and the real calendar date back home.
To avoid this, countries are on either side of the International Date Line which runs down the middle of the Pacific Ocean. If you cross the date line moving east, you subtract a day; whereas if you are moving west you add a day.
The International Date Line
The International Date Line, established in 1884, is an imaginary line of longitude on the Earth’s surface located at about 180 degrees east or west of the Greenwich Meridian. It passes through the middle of the Pacific Ocean, and separates two consecutive calendar years (while the date on one side is January 1 2016, the other side is 31 December 2015).
It is not a perfectly straight line, and has been moved slightly over the years to accommodate the needs and requests of various countries in the Pacific Ocean. Immediately to the left of the International Date Line, the date is always one day ahead of the day immediately to the right of the International Date Line in the Western Hemisphere.
Travelling east across the International Date Line results in a day, or 24 hours, being subtracted. Travelling west across the International Date Line results in a day being added.Though, regions on either side are not exactly a day apart because of local time variations as the map above shows.
Despite its name, the International Date Line has no legal international status, and countries are free to choose the dates that they observe. While the date line generally runs from the North to South Pole, it zigzags around countries such as eastern Russia and Alaska’s Aleutian Islands.
Some Countries Along the IDL That Have Changed Their Dates
Samoa
The Samoan Islands, now divided into Samoa and American Samoa, were west of the IDL until 1892, when American traders persuaded their King Malietoa Laupepa to adopt the American date (3 hours behind California) in replacement of the Asian date (4 hours behind Japan). The change was made by repeating Monday, 4 July 1892.
But in 2011, more than 119 years later, Samoa shifted back west of the IDL by skipping Friday 30 December 2011. The IDL now passes between Samoa and American Samoa, with American Samoa remaining aligned with the American date.
Samoa made the change because Australia and New Zealand have become its biggest trading partners, and also have large communities of expatriates. Being 21 hours behind made business difficult between the two countries.
Tokelau
A territory of New Zealand, and north of Samoa also crossed the IDL at the same time in 2011 to follow Samoa which it is connected to by the only ferry service on that island.
Eastern Kiribati
The Republic of Kiribati, in the Central Pacific, introduced a change of date for its eastern half on 1 January 1995, because prior to this, the country was divided by the IDL.
Upon independence in 1979, it acquired from the United States, Phoenix and Line Islands, which were east of the IDL, while the country itself is just by the IDL. Government offices on opposite sides of the line could only conduct business on four days of the week which were weekdays on both sides. But after the change, the IDL in effect moved eastwards to go around this country.
As a consequence of the 1995 change, Kiribati’s easternmost territory, the Line Islands, including Christmas Island started the year 2000 before any other country.
Keep this in mind the next time you travel around the world!
See Also: Understanding Time Zones: Why is it 3pm in Lagos, but 6am in Los Angeles?
