When the south Pacific nation of Samoa decided to shift the international dateline some distance to the east, in the process losing itself an entire day off the calendar, it was far from the first time the line has moved.

Here's a look at five facts about the line that marks the spot on the globe where the day changes.

It's imaginary.

The international date line is an imaginary north-south line drawn through the middle of the Pacific Ocean about half way around the world, close to the 180 degrees of longitude from the Prime Meridian, which cuts through Greenwich, England.

The date line shown on most maps is the one drawn by the British Admiralty in 1921, according to the U.S. Naval Observatory.

It has no force in international law.

The line is one of convenience — any given day has to start and end somewhere — and it is not recognized as a legal entity. It has no international status, and was not defined at the 1884 Prime Meridian conference in Washington, D.C., or by any other treaty, according to the website of the Royal Observatory in Greenwich.

It zigzags quite a bit.

Countries near the international date line have moved it over the years to take into account their needs or concerns. One of the biggest zigs occurs around Kiribati, an island nation of 32 atolls that straddles the equator. In 1995, Kiribati moved a chunk of the line to the east so that the entire country was on the same side.

For Samoa, the time jump means that its 186,000 citizens, as well as the 1,500 in the three-atoll UN dependency of Tokelau, will be on the same day of the week as most of their main trading partners.

Perhaps more importantly they will now be the first in the world to ring in the new year, rather than the last.

The mid-way point actually crosses very few bits of land.

Three islands that are part of Fiji — Vanua Levu, Rambi and Taveuni — are the only islands actually crossed by the 180-degree line, according to the Royal Observatory in Greenwich. That line also crosses Wrangel Island, part of the far northeast of Russia and Antarctica.

It addresses the phenomenon of gaining or losing a day noticed by circumnavigator Ferdinand Magellan and literary character Phileas Fogg in Jules Verne's Around the World in 80 Days.

When the Portuguese explorer Magellan and his crew returned from their 16th-century westward circumnavigation of the globe, they discovered that one day had somehow been lost. In Verne's 1873 saga, Fogg found that he gained a day in his eastward voyage.