Spell It: Why the international date line swerves and zig-zags its way down the Earth

When thinking about how the Earth is divided by the international date line (IDL), you’d likely guess that it’s a straightforward line, right? Well, wrong.

Click start to play today’s Spell It, where we do a double-take at the ‘atlas’ of the world.

The IDL is the imaginary line that runs from the North Pole to the South Pole, and forms the line of demarcation between two consecutive calendar dates. When you cross it, you either gain or lose a day, depending on which way you’re heading.

The system of time zones was established to allow people from around the world to experience daylight hours in roughly the same amount. It was first proposed by Scottish engineer Sir Sandford Fleming in 1876, to help railway systems become more efficient. The idea of 24 standardised time zones was so practical, it caught on, and by 1900, most industrialised nations around the world had adopted the system.

All of the time zones are numbered eastward, starting from the prime meridian, a longitudinal line that runs directly through the British Royal Observatory in Greenwich, UK. As you keep going east, the time zone increases by an hour.

When the IDL was established in 1884, several resolutions were passed – for instance, countries adopted a universal solar day, counted on a 24-hour clock from midnight at Greenwich, and all nautical and astronomical days would begin at 12am. However, none of the resolutions were binding. It was left to each country to enforce the proposals. Even today, the IDL is not an international law – but it’s so valuable for global connectivity, communication and time measurement, it has become accepted by all nations.

Here's the strange bit, though. The IDL is a line of longitude, but it’s not straight by any means. It roughly follows a 180-degree meridian, halfway around the world. But as it runs down the Earth’s surface, it swerves, sometimes zig-zags, and makes seemingly arbitrary deviations. There’s even a section of it that looks like a hammer jutting out!

But there are practical reasons for why the IDL looks the way it does. For instance, the hammer-like deviation that reaches as far east as the 150-degree meridian, occurs around the Pacific Island nation of Kiribati. When Kiribati received its independence from the UK in 1979, it was a group of 33 islands and atolls spanning at least 5 million square kilometres. But when the IDL was first established, its straight line bisected the island nation, leaving its western side half a day ahead of its eastern side, according to the US-based Central Intelligence Agency’s (CIA) World Fact Book.

What happened next was considerable chaos – the nation tried to conduct normal business with half of its nation a day ahead and the other half a day behind. But by 1995, Kiribati had had enough. The nation’s leaders decided to extend the IDL eastward, creating a hammer-like deviation that finally brough all the country’s islands into one timezone.

So, the next time you take a look at the IDL on the atlas, you’ll know why it swerves and extends in some places.

Did you know about this aspect of the IDL? Play today’s Spell It and tell us at games@gulfnews.com.