Talk:International Date Line

Location

Does anyone have the coordinates of the line? SDSpivey (talk) 23:08, 29 June 2022 (UTC)

Purpose

I've added a paragraph to clarify the purpose of the line, before we get into travel anomalies:

In conjuction with the moving imaginary line opposite the sun corresponding to midnight, the IDL separates the two calendar days being used on earth at any moment (with an anomaly noted below) except when midnight crosses the IDL.

For the purposes of defining timezones, midnight jumps from timezone to timezone, it doesn't move continuously across the Earth's surface. Therefore timezone related definitions, such as IDL, need to be defined in terms of timezones, not astronomical phenomena. — Preceding unsigned comment added by 88.108.90.98 (talk) 22:00, 2 January 2012 (UTC)

Which makes this paragraph almost superfluous:

The line is necessary in order to have a fixed, albeit arbitrary, boundary on the globe where the calendar date advances in the westbound direction.

--Hugh7 (talk) 20:07, 31 December 2011 (UTC)

I have removed edits by 88.108.90.98. The date does not change between +11 and −11. It changes at the IDL regardless of the time zone differences on either side of it. The arbitrary nature of the Greenwich Meridian is different from that of the IDL. Some neighboring time zones do not differ by one hour. 88.108.90.98 does have a valid point that midnight jumps from one time zone to the next discontinuously, but he did not mention that in his edit. Nor is it necessary to mention this in an article about the IDL. — Joe Kress (talk) 05:32, 3 January 2012 (UTC)

IDL is at the boundary between +11 and -11 time zones. That boundary defines the IDL. Therefore the IDL is defined with reference to those TZs. — Preceding unsigned comment added by 88.108.90.98 (talk) 21:44, 3 January 2012 (UTC)

IDL is not necessarily the boundary between -11 and +11, it is the boundary between the far negative and the far positive times zones, which might be -10, -11, -12, +11, +12, +13 or +14, whatever the adjacent countries have defined. Look at the map. The natical date line is between -12 and +12 (not -11 and +11) but the nautical zones are less interesting since both land areas and ships on high seas choose their time based on that they prefer.--BIL (talk) 09:53, 4 January 2012 (UTC)

Further historical citations relevant to the date line

Submitted by drs (talk) 13:47, 4 January 2012 (UTC)

The first Christian Missionaries: Chaplain Crawford of the United States Navy, arriving at Samoa, found that the missionaries who first introduced Christianity there, had forgotten to change their reckoning when they crossed the line, and were keeping the " Christian Sabbath" (Sunday) on Saturday.

The Alaskan Transfer: In the February, 1869 edition of the Overland monthly and Out West magazine C. Delavan Bloodgood describes the Alaska transfer event and surrounding circumstances. This is a primary source; a rich account of those times.

The 1884 Prime Meridian Conference: Shelley et al use two pages to describe the Prime Meridian Conference of 1884. They cites Protocols of the Proceedings, 1884.

Time zone change when crossing the dateline

The lede currently says

A traveler crossing the IDL eastbound subtracts one day, or 24 hours, so that the the calendar date to the west of the line is repeated. Crossing the IDL westbound results in 24 hours being added, advancing the calendar date by one day.

Likewise, paragraph 4 of the Geography section says

If one flies (or sails) around the world from east to west (the same direction as Magellan's voyage), one hour is lost for every 15° of longitude crossed, losing 24 hours for one circuit of the globe; one compensates by adding 24 hours when crossing the International Date Line from east to west. In contrast, a west-to-east circumnavigation of the globe requires subtracting 24 hours when crossing the IDL. The International Date Line must therefore be observed in conjunction with the Earth's time zones: on crossing it, in either direction, the calendar date is adjusted by one day.

But am I correct that crossing the dateline also moves you into a different time zone? If so, then when crossing it while eastbound one sets the clock back 24 hours because of the dateline but simultaneously sets the clock forward one hour because of the time zone change. So it's misleadingly incomplete to say A traveler crossing the IDL eastbound subtracts one day, or 24 hours; and to say that Crossing the IDL westbound results in 24 hours being added, advancing the calendar date by one day is incomplete in its first part and sometimes wrong in its second part -- e.g. if you cross it westbound from, say, a time of 12:30 AM Wednesday, the net effect on the clock/calendar is plus 24 hours minus 1 hour = +23 hours, so your new time/date is 11:30PM on (still) Wednesday. Duoduoduo (talk) 17:11, 6 January 2012 (UTC)

No, you're not exactly correct, but the confusion is understandable. It depends where you cross the dateline. Look at the map in the main article. At some points, crossing the dateline does indeed change time zones in the way you mean (i.e. from one clock time to another). Siberia to Alaska, for example, is a 3 hour clock time difference. But at other points, the dateline bisects a zone of identical clock time where the offset time (from GMT) is +12 on one side of the dateline and -12 on the other. That is the case between the Marshall Islands and the Baker and Howard Islands.

Since the vast majority of people crossing the dateline these days do so by plane, the simple approach is to consider that at the moment when you cross the dateline, the calendar date is advanced (or regressed) by one but the clock time remains the same. 66.28.247.235 (talk) 17:20, 6 January 2012 (UTC)

I thought that you always change time zone when cross the IDL. Even if you go between UTC-12 and UTC+12 because they are different time zones. Also UTC-11 and UTC+13 are different time zones. --BIL (talk) 12:05, 17 January 2012 (UTC)

No, 66.28.247.235 is right. UTC+12 has the same clock time as UTC-12. For example, at 13:00 UTC it is 01:00 UTC+12 (13+12 mod 24) and it is 01:00 UTC-12 (13-12). Duoduoduo (talk) 16:47, 17 January 2012 (UTC)

So, we have two definitions of "time zone", either "area with same clock time", or "area with same clock time and date" same as "area with same time difference against Greenwich". To have two different definitions for the same term and use them interchanged, is always a big source of confusion. In my opinion, hour and day are both units of time, hour = 1/24 day, and should not be separated. 12 hours is not the same as 1 day and 12 hours. Monday 12:00 is not the same time as Sunday 12:00. A person 6ft 2in is taller than one 5ft 2 in. The summary and conclusion: Moving yourself across the IDL moves yourself into a different time zone, around 24 hours difference. --BIL (talk)

Your definition of time zone is certainly reasonable. But I think it was pretty clear in this thread that the discussion was about whether you change your clock when you cross the dateline. Duoduoduo (talk) 22:39, 17 January 2012 (UTC)

Aircraft

The article states 'The nautical date line, which is not the same as the International Date Line, is a de jure construction determined by international agreement. It is the result of the 1917 Anglo-French Conference on Time-keeping at Sea, which recommended that all ships, both military and civilian, adopt hourly standard time zones on the high seas.' Does anyone know what the rule is for time on aircraft? Eg suppose that a plane

(a). Leaves American Samoa (UTC minus 11, X) at 1000 UTC on Sunday, when it is 11PM on Saturday local time (so Sunday has not started yet). And when it is 12 midnight on Sunday/Monday in Tokelau.

(b). And flies to Tokelau (UTC+14:00, M†), arriving at say 1100 UTC on Sunday, when it is 1AM on Monday local time (so Sunday has finished). And when it is 12 midnight on Saturday/Sunday in American Samoa.

(Adjust to whatever the normal duration of such a flight is).
And suppose that a passenger dies halfway through the flight. Does the death certificate show the death on

1. Saturday, being the day at the departure point?

2. Sunday, being the day by UTC?

3. Monday, being the day at the arrival point?

Is it relevant which side of 180' the plane was on at the time? Or in which country the plane is registered?

Alekksandr (talk) 22:47, 15 January 2012 (UTC)

Time used by aircraft when communicating with air traffic controllers and navigating is Coordinated Universal Time (UTC) or Zulu time—time zones are not used unless requested. See for example, the FAA Air Traffic Control manual. Times of births and deaths are probably controlled by some international treaty or by the laws of the parents' or passenger's country. — Joe Kress (talk) 03:05, 17 January 2012 (UTC)

If someone is born or dies onboard, that is probably handled document-wise in the country of landing, so its time zone might be used. --BIL (talk) 19:57, 4 February 2012 (UTC)

Effect on religion

It has been argued [1] [2] 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)

Though the first of those links says 'Footnote: For practical purposes, we would presume that the Sabbath would technically begin on the eastern border of the original Promised Land, and progress westward marked by the exact shadow of the earth. Otherwise, there would have been people keeping the Sabbath on separate days, depending on which side of the city (or nation) they lived on. Of course there is no Biblical or historical record of that having occurred.' IOW, sunset at the River Jordan (east of Jerusalem) is slightly earlier than at Jerusalem. Your argument would mean that the sabbath there would begin almost 24 hours after it began at Jerusalem. Alekksandr (talk) 18:52, 15 January 2012 (UTC)

Copy edits etc.

I have copy edited the article to make it easier to read. Please check that no oversimplifications or errors have been introduced. Michael Glass (talk) 10:53, 3 February 2012 (UTC)

Still pretty dang confusingly written

When you first learn physics, they teach you concepts as if relativity didn't exist--only then do they introduce relativity. Can someone who genuinely understands this concept please explain it as if Tonga, etc. didn't exist and only then introduce it and the other exceptions? I think I'm barely starting to understand but it's still really confusing to me. Matt Yeager ♫ (Talk?) 17:09, 9 April 2012 (UTC)

This is what made me grasp the concept. Say you start in London and keep heading eastwards around the world, through Europe, Asia, etc. As you head east, you enter different time zones and have to alter your watch: +1 hour in France and western Europe, +2 hours in eastern Europe, +3 hours as you enter Russia, and so on, reaching +12 hours by the time you hit the Pacific islands. If the International Date Line didn't exist, and you kept adding an hour to your watch, by the time you got back to England you'd have wound your watch forwards 24 hours, so it would appear to you that your journey round the world had taken a day longer than it actually had (e.g. your watch would say 1pm Tuesday whereas someone who had been in England all the time you were away travelling would tell you it is 1pm Monday). If you kept circumnavigating the world your watch would get one day ahead with each circuit. The IDL stops this from happening by "taking back" those hourly changes. So heading east around the world you advance your watch by 1 hour 24 times, but on the way round you have to wind it back a whole day, which cancels it out and puts you on the right day. Similarly, if you head west, you have to put your watch back 1 hour 24 times on one journey round the world, but you advance it by a whole day when you cross the IDL. Either way, when you return to the starting point you haven't gained or lost any time. 143.252.80.100 (talk) 15:38, 24 July 2012 (UTC)

Very good. I like the link to modern hourly time zones instead of the mean solar time at evey meridian passed which is not well understood any more. Furthermore, I recently ran across good explanations from the 14th century and immediately after Magellan's remaining ships returned, both stating that if no dateline existed a circumnavigating traveler arriving back home would find that his day of the week and date differed by one day from the day and date kept by those who did not travel, if west than one day earlier and if east than one day later. This is already mentioned in the article in the fourth paragraph of Geography, but should be moved to a more prominent place. — Joe Kress (talk) 19:29, 24 July 2012 (UTC)

Move "Samoan Islands and Tokelau" section after "Eastern Kiribati" section

The modern IDL move for Samoan Islands and Tokelau occurred in 2011, whereas the IDL move for Eastern Kiribati occurred in 1995. Therefore, let's move the "Samoan Islands and Tokelau" section after "Eastern Kiribati" section. Wideangle (talk) 05:36, 5 July 2013 (UTC)

UTC

In the second paragraph, the abbreviation UTC is used but is not defined. 87.112.237.138 (talk) 16:21, 6 April 2014 (UTC)

Not Relevant to the International Date Line

Under the "Christianity" section, the first paragraph reads:

Generally, the Christian calendar follows the legal calendar, and Christian churches recognize the authority of the IDL. However, one important issue exists in some Orthodox countries where the Julian calendar is followed for religious purposes, but the Gregorian calendar for civilian purposes. The two calendars have the same weekdays, so the main issue is when to celebrate Easter, Christmas, and other main holidays.

The material in bold, which is everything in the paragraph after the first sentence, has nothing to do with the Date Line and should be removed.

Ignoring the fact there is no such thing as an "Orthodox country" -- the same problem arises in countries where Orthodox Christians are a minority as well as those in which they are a majority -- the question of when Orthodox Churches shall celebrate Easter, Christmas, and so on, is solely an issue for the church calendar. Easter might be on this Sunday or it might be on that Sunday, but it will always be on Sunday. The Date Line has absolutely nothing to do with which Sunday shall be Easter.

The only question that might arise is whether two different countries near to each other but on opposite sides of the Date Line - such as Samoa and American Samoa - were actually observing Easter Sunday on Sunday. This issue would apply to all Christians, not just Orthodox ones.

To wit:

When it is Sunday in Samoa, it is Saturday in American Samoa; and when it is Sunday in American Samoa, it is Monday in Samoa. Thus, Christians in American Samoa will always observe Easter Sunday a day after Christians in Samoa observe Easter Sunday. Does that mean that Samoans "really" celebrate Easter on Saturday (because their Sunday is Saturday in American Samoa); or does it mean that American Samoans "really" celebrate Easter on Monday (because their Sunday is Monday in Samoa)? The settled answer is that all Christians who celebrate Easter, wherever they are in the world, celebrate Easter on Sunday as that day falls in countries located either side of the Date Line.

Likewise, all Christians who celebrate Christmas do so on 25 December. It might be 25 December according to the Gregorian Calendar (which is 12 December on the Julian Calendar) or it might be 25 December on the Julian Calendar (which is 7 January on the Gregorian Calendar). But whichever calendar is used, Christmas will always be 25 December as that date falls in countries on either side of the Date Line.

The Date Line simply plays no role whatsoever in the calendaring of dates for Orthodox Christian holidays. — Preceding unsigned comment added by 73.162.218.153 (talk) 19:57, 29 March 2015 (UTC)

Seventh Day Adventists

Is it worth mentioning the rather interesting events among SDA's on Samoa when it switched back across the date line in 2011? A six day week among Seventh Day Adventists caused quite a stir and a rift, as you can imagine.Farsight001 (talk) 00:44, 8 October 2015 (UTC)

Imaginary?

I don't think it is quite right to describe the line as "imaginary." Imaginary things don't exist, whereas the International Date Line does. Obviously it exists as an artificial human construct and not a physical entity - but then so do many national and state boundaries, which are real enough in human affairs. How about replacing "imaginary" with "notional"? ("The International Date Line (IDL) is a notional line of navigation on the surface of the Earth....") 85.255.233.212 (talk) 20:56, 19 May 2016 (UTC)

@85.25.233.212: I guess I represent the status quo right now as the most active current editor here. For what it's worth, the article has said "imaginary" for a very long time, and people have seemed satisfied with that word. And, interestingly enough, if you look at wikt:notional at definition 1, which is the meaning we're using here, you'll see that "imaginary" is given as a synonym (or near-synonym) in the definition.

I tend to think you're right that at this point in history notional probably shades a little more correctly than imaginary in this setting. So feel free to be WP:BOLD and change it yourself. I won't reverse you. But if others decide that they want to reverse you, I wouldn't start getting into a fight over it. Good luck. StevenJ81 (talk) 21:40, 19 May 2016 (UTC)

IDL basic concepts : one, two, three dates at once

• https://en.wikipedia.org/wiki/File:Earth_map_with_180th_meridian.jpg
• https://upload.wikimedia.org/wikipedia/commons/6/61/International_Date_Line.png
• https://upload.wikimedia.org/wikipedia/commons/8/87/Dateline-animation-3deg-borderonly-180px.gif

The current article does a good job presenting the complex quirky details of the IDL -- but it is very difficult for a new reader to figure out the underlying concepts behind these details.

The most important thing about the IDL is not that travelers who cross the line gain or lose one calendar date. The most important concept behind this line is that it is the boundary between extreme-plus and extreme-minus time zones, and what that implies for dates in different places. It is quite a mental challenge to grasp these basic concepts.

The basic truth is that, conceptually, at 0:00 UTC (midnight in London) the new date starts there, and has already come to half of the globe -- but half of the globe still has the old date. This situation gradually shifts over the next 12 hours. At 12:00 UTC (noon in London) the entire globe would have the same date (if things were maximally simple). The reader needs this basic concept as a framework to add the additional quirks.

The first quirk is that the above simplification would apply if the world were divided into 24 simple time zones, -12 through +11, with the IDL on the boundary between -12 and +11. Then at 12:00 UTC, for one hour, the whole globe would have the same date. However, the antimeridian conceptually is drawn right down the middle of a time zone, just like the zero reference at Greenwich should be right in the middle of that time zone. So, conceptually there are 25 simple time/date zones, from -12 to +12, and at 12:00 UTC, for one hour, the whole globe would have the same date -- except that there would be a sliver of +12 that would already have the next date.

The existence of +12 is thus a complication -- but has the advantage that if the IDL is mostly a boundary between -12 and +12, the time/date difference across that line is 24 hours, so the difference is conveniently exactly one day, with no difference in clock time. But the many quirky details of the real IDL create many more complicated discontinuities.

In reality, we not only have -12 to +12 time zones, but also +12-3/4, +13 and +14. Thus, in reality, at 12:00 UTC (noon in London) there are two dates somewhere, because almost all the globe has one date, but the next date has started in a few places. And we continue to have two dates somewhere, passing 0:00 UTC (midnight in London) when the globe is split about in half by the two dates -- until 10:00 UTC, when the old date is almost over everywhere, but the next date has already started in a few places, so for the next two hours there are actually a total of three dates on the globe.-71.174.190.122 (talk) 15:38, 23 December 2016 (UTC)

I understand the point you are making here. I'll see what I can do in the next few days. StevenJ81 (talk) 15:20, 27 December 2016 (UTC)

Date of transition in Samoa in 1800's

The article quotes 3 modern newspapers in giving that date of transition as 1892, but the IANA time zone database [3] states that it occurred in 1879 referencing a source that references a source from 1883:

Howse [citing Derek Howse, Greenwich time and longitude, Philip Wilson Publishers (1997)] writes (p 153, citing p 10 of the 1883-11-18 New York Herald) that in 1879 the King of Samoa decided to change "the date in his kingdom from the Antipodean to the American system, ordaining - by a masterpiece of diplomatic flattery - that the Fourth of July should be celebrated twice in that year."

If the existence of that statement in the 1883 New York Herald can be confirmed, then it is almost certain that the date of that transition was not in 1892, but 1879. 24.51.171.231 (talk) 22:28, 26 April 2017 (UTC)

Hello, IP address. I've replaced the three modern newspaper citations with a single citation from 1921. The 2011 newspapers didn't go into much detail about the first change (and one didn't even bother to specify the exact year). The 1921 source goes into some detail, including making specific reference to a letter from Samoa dated the "second" July 4, 1892. This is particularly relevant, because the letter is from Robert Louis Stevenson, who didn't move to Samoa until 1890. I agree that it would be helpful to read the original 1883 article in the New York Herald because, if it says what Howse says it says, then we have quite a mystery on our hands. But until then, reliable sources are telling us that the change took place in 1892. By the way, might you provide a direct link to the IANA page that gives the information? The page you linked to doesn't seem to have it. NewYorkActuary (talk) 01:36, 27 April 2017 (UTC)

If you want to read it by HTTP, it is in the file australasia in the compressed file tzdata2017b.tar.gz linked to the at the original link [4]. However, it can be read by ftp at [5]. In both cases search for "(Western) Samoa and American Samoa" after you have opened the australasia file. 24.51.171.231 (talk) 04:21, 27 April 2017 (UTC)

The "Letters from Samoa" cited in the 1921 source states that the 4th of July on which the date line transition took place was a Monday. This implies that the Dominical Letter of that year was B which, within the last quarter of the 19th century, is only correct for 1881, 1887, 1892 and 1898. In 1879, the 4th of July fell on a Friday. AstroLynx (talk) 11:12, 27 April 2017 (UTC)

Checking the Howse publication (online here) is transpires that the year 1879 cited in the IANA timezone database actually refers to Fiji, not to Samoa. The year when Samoa changed is in fact not mentioned by Howse but the reader can be easily be fooled in believing that it was also in 1879. Note that the New York Herald article cited by Howse (his footnote 12) was dated 18 November 1883, the day when clocks in the US were reset to standard time. On the "Day of Two Noons" it would be an appropriate moment to also discuss time-keeping near the anti-prime meridian but, unfortunately, I cannot find the article online anywhere. AstroLynx (talk) 12:23, 27 April 2017 (UTC)

Actually if you look at the situation in the Howse book more carefully, you see that not only is the page number (162, not 153) wrong in the IANA time zone database, but that footnote referred to by IANA time zone database is actually footnote 12 of the previous chapter (chapter 5, rather than chapter 6) [6]. It seems that I was right to want further verification: there appears to be no 1883 claim that Samoa transitioned in 1879. 24.51.171.231 (talk) 14:03, 27 April 2017 (UTC)

The difference in page and chapter numbers is due to the fact that my link refers to the first (1980) edition of Howse's work while the IANA database refers to the 1997 edition. AstroLynx (talk) 14:22, 27 April 2017 (UTC)

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line of navigation?

From the first sentence: "The International Date Line (IDL) is an imaginary line of navigation". How is it a line of navigation? That doesn't seem accurate. I doubt that any vessels (ships or planes) actually use it to navigate. I propose removing "of navigation". Omc (talk) 00:06, 6 March 2018 (UTC)

Point. Edited. StevenJ81 (talk) 15:30, 6 March 2018 (UTC)

Authority

It would be useful to have some indication on which entities are reputable source for the current definition, if any. For example there appears to be a discrepancy between PacIOOS' definition and what Google Maps displays. This is partly based on this video: https://www.youtube.com/watch?v=aBppb2quqkE Ajmasz (talk) 16:15, 11 June 2020 (UTC)

Some more searching on PacIOOS leads me to https://www.pacioos.hawaii.edu/voyager/info/international_date_line.html , which risks being a bit of cyclic definition, in noting "The precise location of the IDL is not fixed by any international law, treaty, or agreement. As a result, various maps and atlases will display it differently (see some examples). We have used the same IDL displayed by Wikipedia". I would imagine the best definition we can have is identifying the time zone selected by each island nation and then drawing the best line possible? Whatever the case is, I feel it would be useful for this to be covered in the actual entry Ajmasz (talk) 16:20, 11 June 2020 (UTC)

Description of longitude of dateline east of New Zealand in error?

In the 2nd to last paragraph of the 'Description' section, it states that (after passing between Samoa and American Samoa) the "IDL follows the 165°W meridian": I believe this should be the 172.5°W meridian. I would like some agreement with this before changing the article. Please comment, anyone. — Preceding unsigned comment added by Jauntymcd (talk • contribs) 00:12, 24 August 2020 (UTC)

De facto or de jure?

The current page refers to national time zones as "de facto" and not "de jure". This contradicts any use of the terms that I have ever seen. "De jure" means "by law", and nearly all time zones are established by law (a very few, like Eucla in Australia, are de facto). In conjunction with the IDL this sounds Just Plain Wrong. Can anybody point to references that claim that national legislated time zones are de facto? Otherwise the section needs reworking. Groogle (talk) 01:28, 1 September 2020 (UTC)

New UTC offsets

A part of Kiribati is in UTC+14:00 exactly one day ahead of Hawaii which uses UTC-10:00.

Current UTC-10:00 (2024-11-30T05:05 UTC−10:00 [refresh])
Current UTC+14:00 (2024-12-01T05:05 UTC+14:00 [refresh])

UTC+13:00 and UTC+14:00 were created in 1995, they should create a UTC+15:00 but they haven't gotten to it or is it too far?

Also where is UTC-09:00 in effect between the second Sunday in March to the first Sunday in November?

--2605:A000:1103:55F:587D:8797:F6B9:B2A (talk) 20:52, 9 September 2020 (UTC)

Date change when crossing IDL

If going west, add a day. If going east, subtract a day. The third and fourth sentences of this article say the opposite and are wrong. 2601:644:8E7F:3F50:F4AB:E044:968C:E9A2 (talk) 05:49, 24 February 2022 (UTC)

The day change (add or subtract a day) also depends on the time of day. When time in the timezone just west of the IDL is 11PM to just before midnight, all the globe is on the same date. Moving between timezones will always change your time of day, but for this one hour interval, the date is constant around the globe.

In general the wording in the lead paragraph

"Crossing the date line eastbound decreases the date by one day, while crossing the date line westbound increases the date."

is correct - except for the one hour described above.

The wording under "Circumnavigating the Globe" is better since it only (and correctly) says: add/subtract 24 hours, without reference to date. I'm updating this section to reflect the date change. LarryLACa (talk) 21:31, 1 August 2024 (UTC)

Looking for an expert of IDL and time zone

I am a children's author working on a book that will include information about the IDL and time zones. I'm looking for an expert in the field that I could talk to and who might serve as a source for my work. Please leave a reply here. Thank you. R.L. Sanders 23.251.65.249 (talk) 13:59, 9 August 2023 (UTC)