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The line in the middle of the ocean that separates time: how islands miles apart a whole day separates them

The day I decided to come to live in the opposite part of the world was also the day that I began to have to deal with time zones, imaginary lines, and “time travel.” For example, I look at the horizon from the beach and what I see is the past. Whereas for me it is Saturday morning, if I took a boat and went there, it would be Friday morning again. Are the peculiarities of the international date change line.

To have a standard with which to measure time at different points on the globe, what we have done is to divide it into smaller pieces. If it takes 24 hours for the Earth to make a full rotation and a full day, we have divided it into 24 smaller pieces following the meridians of the globe. With this we get it to be a certain time of day when the Sun is at a certain height in almost all parts of the world.

This, in general lines and without entering the exceptions or the summer and winter schedules, allows us to have different time zones. As we move east we add hours, as we move west we subtract hours. Hence, in the Canary Islands they have one hour less (because they are much further west) and eastern Europe generally one hour more (because they are further east). The problem however is in the other part of the world.


We have an obsession with classifying, separating and standardizing.

An imaginary line that goes from the North Pole to the South Pole and through the United Kingdom and Spain among other countries is the one that marks how the days should be measured. Its about Greenwich meridian and allows us to add or subtract hours depending on whether we go east or west. It is also the point where, when it is broad daylight at 12:00 PM, the rest of the world is on the same day. Of course, while moving from one side of Greenwich to the other implies jumping for an hour, on the opposite side of the globe we jump during the day.

Traveling the 180 ° meridian

The 180 ° meridian is the virtual line opposite Greenwich and starting point of the day. It is known as the international date change line and it is a line that not only separates time into hours but also into a full day. A person can pass from Monday to Tuesday crossing that line in a westerly direction, or from Tuesday to Monday if he crosses it in an easterly direction. Technically it is traveling to the future or the past and you just have to swim, take a boat or go by plane.

Like many other virtual lines and borders, the international date change line does not follow a perfect straight line through the Earth from pole to pole along the 180 ° meridian. The line begins straight across the North Pole until it reaches a small island in Russia, which is when it moves east to encompass all of Russia at the same time. After all, it would be strange if one town is Friday and the other is on the weekend.

The line therefore goes through the middle separating Russia from Alaska (United States), just between two islands separated by 3.8 km apart. These are the islands of Diomede (Russia) and Little Diomede (United States). If one goes from one island to the other, the day changes, and in fact the swimmer Lynne Cox did it in 1987 at 3 ° C in an event to symbolize the gesture of peace between both superpowers. It took two hours and five minutes, although technically it took an entire day.


Continuing with the peculiar imaginary line, it moves west again this time to collect the multiple islands that Alaska has in the Russian part at the same time. One thinks that these islands would be the farthest west that the United States has in the world, but in reality they are the farthest east, having passed the 180 ° meridian. The line, after this zig-zag, return to the 180 ° meridian and it goes down in a straight line until it reaches Polynesia.

In Polynesia things get complicated again. It is a gigantic area in the vast Pacific Ocean that encompasses hundreds of small islands and small countries. Many of these Polynesian countries have several islands scattered throughout the ocean, with the meridian passing right in the middle. For political, economic and social reasons, this is not convenient. That is, imagine working for a company that has offices in Madrid and Barcelona, ​​if the international date change line were in the middle, they would be working in Madrid on a Friday but in Barcelona it would be the weekend and impossible to communicate with them by labor issues. If there were already problems when they had two different hours, imagine with different days.

The theoretical 17th century train to travel from Spain to New Zealand in 42 minutes

It is not only a national issue, but also an international one. Many of these tiny nations have a strong dependence on New Zealand for economic issues. Therefore, lit is convenient to be on the same day as New Zealand. To avoid such problems, the line once again takes a gigantic detour to accommodate essentially all the islands of Kiribati. Then, so that other nations such as Fiji, Tuvalu, Tonga or Samoa do not encounter the same problem, the line goes down in a straight line but much more to the east of the 180 ° meridian. At the end, it goes back to 180 ° and goes down to Antarctica.


With the 180 ° meridian being an accurate standard, why does the international date line skip it so much? The reason is very simple: because it really doesn’t matter much. Unlike other borders, this line simply defines deciding to be on one day or another. As we have seen, it can have implications when you change from a working day to one that is not. But beyond that, it is not like a border that separates the natural resources available in one territory or another. Dawn is the same on one island and on the other, although for one it is Saturday and for the other Friday. And it is a very beautiful sunrise.

More information | Knowledge Stew, Mirror, NASA