A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2011 Feb 11, 06:41 -0800
John H, you wrote:
"I'm not sure I'd call it a fiction - it's a political boundary and frequently shifts."
Maybe I can explain better. It is "largely" a cartographic fiction (with one exception --see below). It is not a political boundary, but when mapmakers draw it onto globes and maps, they frequently use certain certain traditional "pseudo-borders" in the Pacific as the basis for their sketches. As for shifting "frequently", well, that's all a matter of degree, but in fact even if you stretch the story, the IDL has changed only rarely. You probably know I make my living drawing historical political boundaries and in particular their changes over time (see www.HistoricalAtlas.com) and I can assure you that the changes in the International Date Line, as drawn on maps and globes, have been rare and determined largely by the whims of the map-making culture.
And you wrote:
"One of the more amusing shifts is being the "first" to usher in the New Year."
Not just any New Year, but New Year's 2000. Since that was such a big media event, the geographically large, but otherwise tiny, Pacific nation of Kiribati (pronounced like "keer-a-bus", derived from "Gilberts", for those following along who might not be familiar with it) legislated that it would keep the eastern hemisphere date in the late 1990s thus enabling it to lay claim to being the first nation on Earth to ring in the year 2000. In fact, if you read that post in the archives from 1999 which I included in my last message, you will find that this is exactly the issue that got Robert van Gent interested in compiling a history of the International Date Line.
"If I were approaching the island of Tonga and wanted to know how to set my watch, I'd like to know what time zone they've legislated themselves to be in. From that point of view I wouldn't call it a fiction."
Aha, but you see, by your very own setup here, you're demonstrating that the line itself, hundreds of miles out to sea as usually drawn, has no importance to you. What you want to know is how to set your clock and read your calendar AFTER you arrive (or perhaps a little earlier, when you begin chatting on the radio with local port authorities --if you're reserving a spot in a marina, you would want to get the days right). This is really no different from knowing the local currency exchange rate. We don't cross lines in mid-ocean where we change from one currency to another. And, with one exception, there's no cause to bother with the date line at sea. The exception is the mariners' traditional rule, supported by international regulations and rules, which says (last I checked) that vessels crossing the Pacific should change the date at 180 degrees longitude. This is the only date line that has any meaning as a line on a map. The various bumps and indentations that you'll find in the traditional IDL on modern maps and globes are not used by anyone, except maybe for amusement. A ship traversing the mid-Pacific passing through the archipelago of Kiribati would have no reason to adjust its date unless it is making a port call. The completely arbitrary boundaries for an imagined "new" IDL are based on various lines drawn around Kiribati by some mapmakers just so that they can have some convenient way of putting a perimeter around the islands that constitute Kiribati. These lines have no basis in international law. There IS NO well-defined International Date Line. It is indeed a cartographer's fiction.
The best historical example of this issue is the case of the Philippines. Until 1845, because it was ruled by Spain as part of the New World colonies, it kept the American (western hemisphere) date. Does this mean that there was some torturously drawn line that ran along 180 and then cut far to the west in order to keep the Philippines on one side of it? Of course not. The obsession with drawing a specific line did not begin until about 1900. There was no International Date Line in the mid-a9th century, nor did anyone need one. Vessels crossing the Pacific from east to west would decide on their own when to reset the calendar if they were making a circum-navigation or heading much further west. But if they were departing from New England (think whaleships) heading out to the West Pacific by way of Cape Horn and then returning to New England, then they would never have any cause to reset their calendars. Indeed the biggest change they had to worry about was the practice of keeping a "nautical day" in that era. The date was changed at NOON in a nautical day and when a ship entered port for any extended period, it was necessary to switch to a civil day. Thus you'll find references in old logbooks to "a day of twelve hours" or "a day of eighteen hours" when they would switch from one time-keeping system to the other.
There's a related modern issue: what time zone lines should we draw that cover the entire globe including the oceans? There is no right answer. The time zones recognized by mariners at sea (of limited value in any case) cannot be reconciled with the time zone borders on land. The Indian Ocean is probably the best case of this with various half-hour time zone differences and some islands on a time zone to the east, others on a zone to the west. Maybe a little more familiar, the dividing line between Zulu (Greenwich Time) and zone N or "November" (the first time zone to the west of Greenwich) runs along 7.5 degrees West longitude which passes right through the middle of Ireland. But all of Ireland keeps GMT (last I checked!). So what would you draw then? A border that runs along 7.5 west and then makes a nice box around Ireland? Or perhaps one that follows a sea line determined by the 30-mile limit away from all points of the Irish coast and islands or one that follows the 200-mile limit? The time zone lines used by cartographers, at a global level, are drawn merely to be helpful --so that a user can determine "at a glance" what time zone is used in a particular island group. They are not definitive or legal. They vary from one map publisher to another.
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