Taylor Swift flies to Las Vegas from Japan and beneficial properties a number of hours. Hong Kong’s inventory market closes as London’s opens. A clock on a distant Pacific island strikes midnight 24 hours early on a politician’s order.
None of these occasions are empirical scientific info. People have simply agreed to watch time zones, an idea promoted by railroad corporations within the nineteenth century.
However time zones have bodily dimensions. So the place precisely on earth do days start and finish? The quick reply is that Mondays develop into Tuesdays on the worldwide date line, a boundary that runs by way of the Pacific Ocean.
The longer reply is that no worldwide guidelines govern the placement of the date line, and its precise coordinates depend upon the shifting whims of governments. Maps that try to depict it are by no means fairly proper, and the road itself technically doesn’t exist.
Confused? Right here’s a primer.
Folks have been speaking about this for hundreds of years.
The concept of building a line the place days start and finish has been round since a minimum of the 1300s. However whereas the Equator is a logical divider of the northern and southern hemispheres, there isn’t any apparent place to divide the jap and western ones.
Mapmakers lengthy selected their very own east-west dividing traces, that are referred to as meridians, a phrase derived from the Latin for “noon.” Within the absence of a global normal for when days started or ended, navigators on lengthy crusing voyages needed to resolve for themselves the best way to account for the time they had been dropping or gaining.
A Sixteenth-century account of a voyage by the English explorer and pirate Francis Drake described a ship arriving on a Sunday. However in “the extraordinary reckoning of those who had stayed at residence in a single place or countrie,” it was already Monday.
The date line’s location was by no means settled.
In 1884, 25 nations handed a decision calling for a “prime” meridian that set zero levels longitude at Greenwich — a city on London’s outskirts that had a royal observatory — so as to set up a global reference level for mapmakers, timekeepers and prepare schedulers. Additionally they resolved to ascertain a “common day.”
However it took many years for a lot of international locations to simply accept the prime meridian and to formalize Greenwich-linked time zones, based on the 2007 e book “One Time Suits All” by Ian R. Bartky. And the bodily location of that common day — the worldwide date line — was by no means formally settled.
In 1921, the British Admiralty, which managed the UK’s naval affairs, stated that no date line had “ever been positively laid down, both by anybody energy or by worldwide settlement.” That’s nonetheless true greater than a century later.
“Whereas the Prime Meridian feels sacrosanct, the worldwide date line isn’t a meridian; it’s fairly arbitrary,” Tim Montenyohl, a cartographer who has mapped the date line, wrote in 2018.
Some international locations have moved the date line.
Because the idea of the worldwide date line just isn’t enforced by a global treaty, international locations and territories within the Pacific are basically free to resolve which aspect of it to position themselves on. Some have switched sides for political or business causes.
Spain initially put the Philippines, its colony from the Sixteenth century, on the jap aspect of the time change. That basically pressured the date line to dogleg west from the one hundred and eightieth meridian. However in 1844, the Philippines moved the road again by declaring that the day Dec. 31 that 12 months would “be dropped, as if it had actually handed.”
Some Pacific island nations have unilaterally moved the date line so as to simplify native time-keeping or to spice up buying and selling relationships inside the Asia-Pacific area.
Within the Nineteen Nineties, Kiribati moved the road east throughout the 180-degree meridian to incorporate its easternmost islands. In 2011, Samoa — which, on the urging of American merchants, had hopped throughout the identical meridian in 1892 by observing the identical Monday twice — skipped again by slicing a Friday.
Emma Veve, an economist on the Asian Growth Financial institution who has labored within the Pacific islands, stated that Samoa’s change made business sense as a result of it put the nation in the identical enterprise day as New Zealand. Whereas the information media made a fuss, she stated, individuals went on with their lives.
The dateline nonetheless challenges map makers.
For map makers — and reporters — the worldwide date line may be arduous to pin down.
Cartographers sometimes map it by consulting different maps, together with a time zone one printed by the Central Intelligence Company. However making a extra granular model is sophisticated, Mr. Montenyohl stated. That’s partly as a result of international locations change time zones; digital maps are likely to mirror flaws of the predigital ones they had been based mostly upon; and a rustic’s territory extends 200 nautical miles from its land boundaries.
“It in a short time type of, like, breaks your mind should you get too deep into the weeds,” he stated.
Right here’s a enjoyable instance.
In 2020, the journalist Johnny Harris observed a discrepancy between two renderings of the date line round a number of the Cook dinner Islands, within the South Pacific.
“Google says that these islands are on the Tuesday aspect, the one-day-ahead aspect, whereas PacIOOS says that these are on the Monday aspect, which means the one-day-behind aspect,” Mr. Harris stated in a YouTube video, referring to the Pacific Islands Ocean Observing System, a nonprofit based mostly in Hawaii.
So which model is true? It’s nonetheless not fully clear.
A spokeswoman for the Cook dinner Islands authorities didn’t reply the query. A spokesman for Google stated solely that the corporate’s maps of the date line had been up to date since 2020. And an information techniques engineer at PacIOOS stated that the group’s model was not a gold normal.
“We’re actually no consultants or authority on the dateline,” stated the engineer, John Maurer. He added that PacIOOS has used the identical model as Wikipedia.
Wikipedia’s model consists of the disclaimer that it “wants extra citations for verification.”
