Talk:International Date Line

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[edit] Getting the Adjustment Right

I was in the midst of an edit to be summarized as

Copyedit the marvelous enhancement; move interlang link to top; add'l copyediting

and my edited text was to be

The international date line is an imaginary line that for the most part is at ±180° Longitude, but has an odd shape to pass around Russia and islands in the Pacific. It is on the side of the Earth that lies opposite the prime meridian. Its purpose is to offset the hours that are added as one travels east through each successive time zone.
The first phenomenon to occur in association with the date-line problem was part of Magellan's circumnavigation of the globe. The crew returned to a Spanish stopover on what had to be a Thursday, as attested by various carefully maintained sailing logs. Nevertheless, those on land insisted it was a Wednesday. Although readily understandable, this phenomenon caused great excitement at the time, to the extent that a special delegation was sent to the Pope to explain this oddity to him.
Warning: Wikipedia contains spoilers
The effect of ignoring the date line is also seen in Jules Verne's work of fiction Around the World in Eighty Days, in which the travellers return to London after a trip around the world, thinking that they have lost the bet that is the central premise of the story. Having circumnavigated in the direction opposite Magellan's, they believe the date there to be one day later than what it truly is.
Anyone travelling west and passing the line must add a day to what they would otherwise expect the date and time to be. Correspondingly, those going east must subtract a day. Magellan's crew and Verne's travellers each neglected those adjustments, respectively.

However, i realized at that point that the marvelous account just added by the previous editor (which i touched up as above but treated as essentially accurate) has Magellan's crew (who travelled west) believing in a date that was too advanced, and needing to subtract a day (Thursday minus a day is Wednesday) to get right. I.e., needing to make the same adjustment i asserted Verne's characters did, despite travelling the opposite direction i asserted they did.

[edit] Marshalling the Evidence of a Mistake

  • As you go west, you turn your clock back (make the time you believe in less) by an hour for every 15° of longitude, bcz the sun is not as far toward sunset as you would expect if you made no adjustment. Therefore you have turned back by 24 hours after 360° of westward travel, and to get even with people who didn't travel, you need to "turn your calender" forward (not back) by a day. If your count of days says it's Thursday, the lubbers will agree it's Friday, not Wednesday.
That going round the earth westward was winning one day: upon their return they observed a mismatch of one day between their calendars and those who did not travel, even though they faithfully maintained their ship's log.
"Winning a day" is ambiguous: is it analogous to your "gaining an hour's sleep" when you set the clock back in the fall, or to your clock's "gaining an hour" when you set it forward in the spring? Therefore not evidence either way. But possibly this source of confusion explains the contributor's making what i am calling an error: they misinterpreted "won a day", and assumed the wrong direction for the adjustment the article is describing.
  • I'm a tad embarrassed to admit what the gut-level clincher for me is: i read Verne's story before i was 12 years old, and distinctly remember them landing in San Francisco, continuing east, and finding things getting easier as they got to the more technologized portions of the US, just before their last sea-travel to London. Eastward travel. And the plot falls apart if their calendar needs to be turned forward a day: they think they are a half day late, losing the bet, and it is by turning their calendar back that they realize they've won by a half day margin.

My version:

  • traveling westbound, turn your clock backward when changing time zones, and your calendar forward when crossing the Line
  • traveling eastbound, turn your clock forward when changing time zones, and your calendar backward when crossing the Line

(Unless i'm the confused one, maybe those two formulas belong side by side in the article!)

[edit] What to Do

I'm leaving this apparently erroneous version here, if only bcz i don't know how to fix it: assuming i'm right about the direction of the error,should it be

  • "ship Wednesday, shore Thursday" (error was just reversing the days)
  • "ship Tuesday, shore Wednesday" (error was in deducing ship date from shore one)
  • "ship Thursday, shore Friday" (error was in deducing shore date from ship one)
  • something else (one of the days was chosen at random as a mere example, or both days of week came from mistake in the tricky calculation from Zeller's congruence, or (unlikely, since Spain and Portugal made Julian-to-Gregorian shift while Columbus was at see) using the wrong calendar system.

And avoiding specific days of the week, but referring to the date given in the Magellan article. (I like the reference to days of the week, but let's get agreed about the direction of the correction, then about the days of the week, before putting that back in.)

As to the direction of the correction, i'm leaving my version of Verne as is, and making it vague as to Magellan: better to leave a possible old error in a little longer than to risk going back and forth; the info i'm removing has not been here long enuf for anyone to get used to it. --204.60.201.122 Jerzy 07:02, 14 Jan 2004 (UTC)

[edit] A new day is born

I think the article could mention more clearly that each day springs into excistance at the IDL and then circles the globe westward, as the clock in each timezone reaches 00:00. Ie there are always two "date lines": the IDL and the 23:00/00:00 TZ line. A 3D animation of a globe with timezones changing colors to represent the span of a day would be really fancy.

[edit] Kiribati days

I updated the number of days that Kirbati's government offices could communicate from three to four per week, as this chart will show is correct:

Asian side/American side Sunday/Saturday Monday/Sunday Tuesday/Monday Wednesday/Tuesday Thursday/Wednesday Friday/Thursday Saturday/Friday

There are four days where each is on a weekday.

[edit] Removed from article

"The Flora Commission, a special U.N. Commission under the direction of B. Joseph Flora of Fair Oaks, California, determined that this inefficiency could no longer be tolerated, as it would serve as an adverse precedent for attempts to increase government efficiency in developing countries." Sole contrib from an anon that I can't verify. Niteowlneils 03:21, 10 Dec 2004 (UTC)

[edit] Graphic

Image:International_Date_Line.png is horrible: asking for the enlargement instead of the thumbnail goes to the image page, which starts out readable with MS IE, but once enuf of it has downloaded, it is too tall for the screen and IE collapses it back to something insignificantly different from the thumbnail. It could only be improved if someone butchered with MS Paint to replace the lettering with something readably large.

--Jerzy·t 30 June 2005 20:56 (UTC)

You have two options: 1) Move the cursor to the lower right-hand corner of the collapsed image, and when the resize icon appears, click it. 2) Go to Tools | Internet Options | Advanced | Multimedia, and uncheck Enable Automatic Image Resizing. — Joe Kress 1 July 2005 05:58 (UTC)

Without irony, Thanks. That was an informative IDL & IE exercise.
But it is still not a substitute for a user-friendly graphic.
--Jerzy·t 1 July 2005 14:55 (UTC)

The graphic also needs a revision to reflect Kiribati's use of the +12, +13, and +14 time zones. Chonak 14:32, 13 August 2006 (UTC)

[edit] Tonga to Samoa

There are several problems with the following paragraph in the article:

The International Date Line can cause confusion among airline travelers. The most troublesome situation usually occurs with short journeys from west to east. For example, to travel from Tonga to Samoa by air takes approximately two hours. Thus, if a person leaves at noon on Tuesday, they will arrive at 2 pm on Monday. Meanwhile, someone in Samoa inquiring about the departing flight may be told there is no flight until the next day. There could also be problems with the traveler having to repeat Monday. Journal entries and photographs may end up out of sequence, and there could be errors in someone's medication schedule. In addition, those making connecting flights might choose the wrong date for the reservation.

  • The paragraph as written is in large part unencyclopedic, and would fit better in a travel guide or something like that. "Problems ... having to repeat Monday"? "Journal entries and photographs ... out of sequence"?
  • According to the map that accompanies the article, Samoa is one hour ahead of Tonga on the clock (leaving aside the calendar date): Tonga is shown as +13 and Samoa as -10. So a two-hour flight that leaves at noon Tuesday would arrive at 3 p.m. Monday local time, not 2 p.m. Never mind, it looks like the -10 notation applies to Tokelau and Samoa is actually -11. Still doesn't make this paragraph much better though.
  • Why is it more troublesome to go west to east and repeat a calendar day than to go east to west and "lose" a day?

I've never travelled between Tonga and Samoa (in either direction) and I don't know if the flight is really two hours, but even if that part is accurate the rest of this paragraph needs a considerable rewrite, if not deletion altogether. I doubt that an airline clerk would be so unaware of the issue as to tell a hapless caller that there's no flight till the next day when the flight in question is actually winging its way over the blue Pacific, but the whole statement is completely unverifiable anyway. There's no question that crossing the Date Line can be confusing for air travellers who haven't done it much, but this isn't a very good way to clear up the confusion. -EDM 23:33, 20 September 2005 (UTC)


[edit] First land to the west

The article claims Caroline Island to be the closest land to the west (and thus the first land to see a new date). The article on the Diomede Islands claims that the International date line passes between Big Diomede island and Little Diomede island at a distance of only 1.25mi from each island. The closest land to the date line on the west would need to be Big Diomede island unless someone can make a claim to knowing of land closer than 1.25mi.

This page [1] support Caroline Island. I'm not convinced. I just think the Diomede islands have been forgotten in the discussion.

Robertbrockway 02:31, 5 February 2006 (UTC)

I can't find any such statement regarding Caroline Atoll, only the statement that it is the easternmost part of Kiribati. An appropriate statement might be that Caroline Atoll is the island farthest east of 180° that is still west of the IDL. The territorial waters east of Caroline Island must be included within Kiribati's time zone and hence the IDL would be at least 12 nautical miles farther east, if not farther. This makes the closest island to the west of the IDL Big Diomede.
But if you include all land, then Antarctica is the closest land west of the IDL. Although de jure time zones are not used in Antarctica, de facto zones are because all stations in Antarctica keep the time of their supply bases. The Amundsen-Scott South Pole Station, which keeps New Zealand time, effectively surrounds the pole—the semicircular taxiway connected to its main aircraft runway actually surrounds the pole [2]. This effectively prevents the IDL from touching the pole. It would require complex wording to describe this weird situation. — Joe Kress 12:03, 9 February 2006 (UTC)
  • The first land to see a new date are the Line Islands, all of them, since they have the highest time zone, UTC+14.  
  • One of those islands is the Caroline Island which is the first land to see the sun a new day (several hours after midnight).  
  • The Big Diomede Island is the land that is closest to the IDL, and the only place you could see land across the line. It has time zone UTC+12 (UTC+13 in the summer).
  • Antarctica has no time zones, except the bases which have de facto time zones. But the bases are so sparsely located in the interior and near the IDL landing so you can't define the placement of the IDL.
  • The IDL ends somewhere in Antarctica but not at a defined place for the same reason, mostly no defined time zone. It does not end at the South pole, which has a time zone for its surroundings. Hope I made things clearer. /BIL 11:40, 29 March 2006 (UTC)
Thanks guys for the great explanation. Makes sense. Robert Brockway 05:37, 13 August 2006 (UTC)
Caroline Island never claimed that it was the closest land to the west of the IDL; if you read the article carefully, it claims that Caroline is the "easternmost land west of the International Date Line" (or did, before Robert removed that statement). -- Seth Ilys 19:48, 13 August 2006 (UTC)
One addition to my list: The first place to see the sun a given day is, during the summer, the Chukotka peninsula (midnight sun) or the Big Diomede Island (almost midnight sun), not sure which place. / BIL 09:59, 14 August 2006 (UTC)

[edit] Rephrasing needed?

Ships must adopt the standard time of a country etc.

Does that imply that a ship's captain must change the clocks on board? Why is this? If I decide to cross the channel without without adjusting my watch, or if I don't adjust it for DST, I'm free to do so. What my watch says also has no impact on the actual time. Even if my watch has it 14:07, if the government says it's noon, it's noon.

So what I think is more logical, is that the time aboard a ship changes, regardless of whether the captain decides to change the clocks. Of course, nowadays with computers and GPS and all that applying the proper time to a ship's clocks may have become easier, but one might imagine that a ship just passing through the territorial waters of some island may not bother to tell its crew to adjust their watches. Shinobu 18:30, 12 December 2006 (UTC)

The reason for the shift is that whenever a ship is within the territorial waters of a another nation but does not plan to stop at one of its ports, it is engaging in "innocent passage". This means that the ship is not subject to the laws of the nation (like being boarded) provided that it obeys all navigational rules of that nation, including communicating with the nation on its own time. If it failed to do so, it would be violating the treaty and would be subject to immediate boarding and seizure. I suppose it is possible that only the captain's clock needs changing, but if the crewmen do not change their watches to match the captain's, serious navigational errors could result. Of course, if the ship plans to dock at a port, all of its clocks and watches must change or there would be total chaos as it tried to unload and load its cargo, including passengers. — Joe Kress 04:55, 13 December 2006 (UTC)

[edit] Original research

The following paragraph is original research:

  • However, even into the 21st century, some maps (including the CIA map of the Standard Time Zones of the World)[1] ignore this Kiribati dateline shift and continue to represent the International Date as a straight line in the Kiribati area.

The source cited does not directly support the claim: it doesn't even mention the Kiribati dateline shift. Jakew 23:34, 31 August 2007 (UTC)

The cited source clearly shows that the date line is a straight line in the Kiribati area. That source is dated 5-07, within the 21st century and long after 1995 when Kiribati adopted a single date. Of course the source does not mention the Kiribati dateline shift, because that is what "ignore the Kiribati dateline shift" means. Hence the statement is not OR. — Joe Kress 06:26, 1 September 2007 (UTC)
"Original research includes editors' personal views, political opinions, and any unpublished analysis or synthesis of published material that appears to advance a position. That is, any facts, opinions, interpretations, definitions, and arguments published by Wikipedia must already have been published by a reliable publication in relation to the topic of the article." (WP:NOR, emph added).
So, if the above is not original research then we should be able to attribute the analysis to a reliable source (we need to be able to say something like: "Dr A. Datelinecommenter comments that 'remarkably, many recent maps still continue to ignore the Kiribati shift'"). Jakew 10:13, 1 September 2007 (UTC)
Source found. Fixed. Jakew 10:34, 1 September 2007 (UTC)

[edit] Effect on religion

It has been argued [3] [4] that the International Date Line is a tool of Satan intended to disrupt the correct observation of the Sabbath. I find this highly amusing, but I don't know whether it's appropriate for the main article. Jruderman 10:23, 5 November 2007 (UTC)

Jews have a similar problem with the International Date Line vis-a-vis the Sabbath, although they do not restrict to Jerusalem only, but change at 180° from Jerusalem (possibly faulty memory). — Joe Kress 07:53, 7 November 2007 (UTC)
An international date line can't be avoided. Somewhere there has to be a border between areas with a time zone more than UTC and those less than UTC. The only way to avoid the problem with the correct sabbath day is telling everyone to have the same time zone, e.g. Greenwich or Jerusalem time. Or make the earth flat. At midnight/date shift in Jerusalem there is neccesarily daytime in the Pacific ocean, causing confusing date handling. --BIL (talk) 13:04, 30 April 2008 (UTC)
It is obvious from your two links that correct time zone at least on the Sabbath day is Jerusalem time all over the world. The Sabbath day begins when there is sunset in Jerusalem. --BIL (talk) 13:10, 30 April 2008 (UTC)

[edit] Kiribati and the year 2000--Tonga

It is not entirely correct that "...Kiribati, by virtue of its easternmost possession, uninhabited Caroline Atoll at 150°25′ west, started the year 2000 on its territory before any other country on earth, ..." Tonga has an odd time zone to begin with--west of the Dateline, but the time itself shifted to one zone east, i.e. earlier.

In order, apparently, to have his country be the first to see the year 2000, the King of Tonga instituted Daylight Saving Time, for the first time ever in that country. Tonga being in the southern hemisphere, January 1 is, technically summer. On the other hand, Daylight Saving Time doesn't really make much sense in the tropics since the length of the days and nights through the year changes less and less as you get nearer the equator.

I seem to remember reading that His Majesty was very annoyed when Kiribati shifted the Dateline within its own territory--presumably for the very practical reason of having the whole country on the same side of the line. But the shift meant that the Caroline Atoll now had the same time as Tonga on Daylight Saving Time. So Tonga was not THE first, but one of the TWO first to see 2000.

I watched much of the television broadcast of the year 2000 arriving in time zones around the world. For the very first arrival of 2000, they had a split screen showing both Tonga and Kiribati. 140.147.160.78 (talk) 18:46, 23 November 2007 (UTC)Stephen Kosciesza

[edit] I'm confused -- and I'm probably not alone ...

Someone who understands this should probably add a paragraph explicitly explaining the following question:

Why isn't the Greenwich Mean Line also the date line?

Isn't that where the date changes (Monday to the east, Sunday to the West)?

I thank you in advance. —Preceding unsigned comment added by 68.9.119.36 (talk) 16:19, 22 March 2008 (UTC)

That would be plain silly, it would mean while it was Monday in Germany it would still be Sunday in Britain, tiotally impractical. Its in the Pacific because few people live there. Thanks, SqueakBox 16:25, 22 March 2008 (UTC)
The Greenwich Meridian is the "middle" of the Earth, and so the "middle" of the day (noon). That means that the other side of the world is midnight-the start of a new day or end of the old day. Or in this case, both. —ScouterSig 16:31, 22 March 2008 (UTC)
It would make sense to have located the Prime Meridian in the same place as the International Date Line. I don't think the anonymous post-er is suggesting that that should be in England, but the opposite, where both lines are in the same place in the middle of the Pacific. I wonder if there's another reason for that other than the obvious fact that politically England was considered (or considered itself) to be the "center" of the world during the time the standards were put in place? --Shubopshadangalang (talk) 23:11, 28 April 2008 (UTC)
The Prime Meridian is located where it is because the United Kingdom used this Prime Meridian, and it became a world standard since it is impractical with several. The United Kingdom was dominant during the time when the decision was made (in 1884 with support from the United States). Read Prime Meridian. The international date line is where it is because the dominant calendar is European and the European colonies wanted to have the same date as Europe as closely as possible. The decision of what time zone and date to have in each colony placed the date line in the Pacific ocean. --BIL (talk) 06:45, 29 April 2008 (UTC)
During the International Meridian Conference, it was indeed proposed that both the Prime Meridian and the International Date Line be located in the middle of the Pacific Ocean, but that proposal was rejected. — Joe Kress (talk) 16:42, 29 April 2008 (UTC)