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Thread: Date Line discussion

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    Google Earth Explorer T.Dooley's Avatar
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    Default Date Line discussion

    This is a discussion thread for the following file:

    Date Line

    The International Date Line (IDL) is an imaginary line on the surface of the earth opposite the prime meridian where the date will change as one travels east or west across it. Roughly along 180░ longitude, the anti meridian, with diversions to pass around some territories and island groups, it mostly corresponds to the time zone boundary separating +12 and -12 hours of Coordinated Universal Time (UTC) also known as Greenwich Mean Time (GMT). Crossing the IDL traveling east results in a day or approximately 24 hours being subtracted, and crossing towards west results in a day being added. The exact number of hours depends on the time zones.

    The International Date Line can cause confusion among especially airline travelers. The most troublesome and odd situations usually occurs with short journeys from west to east. To travel from Tonga to (American) Samoa by air, for example, takes approximately two hours but involves crossing the International Date Line, causing passengers to arrive the day before they left. This often causes confusion in travel schedules, like hotel bookings unless those schedules quote times in UTC, but they typically do not since they must match domestic travel times, local transport, or meeting times.

    The first date line problem occurred in association with the circumnavigation of the globe by Magellan's expedition (1519-1522). The surviving crew returned to a Spanish stopover sure of the day of the week, as attested by various carefully maintained sailing logs. Nevertheless, those on land insisted the day was different. This phenomenon, now readily understandable, caused great excitement and confusion at the time, to the extent that a special delegation was sent to the Pope to explain this temporal oddity to him.

    The effect of ignoring the date line is also seen in Jules Verne's book "Around the World in Eighty Days", in which the travelers, led by Phileas Fogg, 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 traveled the direction opposite to the one taken by Magellan, they believe the date there to be one day later than it truly is.

    If someone circumnavigate the globe in an airplane from east to west (the same direction as Magellan), they should subtract one hour for every 15░ of longitude crossed, losing 24 hours for one circuit of the globe; but 24 hours are added the moment the International Date Line is crossed from east to west. The International Date Line must therefore be observed in conjunction with Earth's time zones: the net adjustment to one's watch is zero. If one crosses the date line at precisely midnight, going westward, one skips an entire day; while going eastward, one repeats the entire day.

    When you travel from west to east and cross the IDL; Shift to the previous calendar date / set back your clock approximately 24 hours. When traveling from east to west; Shift to the next calendar day / set your clock approximately 24 hours forward when crossing the IDL. The date of where you are right now is rather well defined, also when you go back and forth across the Date Line as it depend solely on your geographically coordinates. Your current clock adjustment to local time is much more depending on local currently active or inactive agreements like daylight saving time of the location of where you currently come from and the destination you arrive to.

    Because the agreed IDL do not follow the 180░ longitude in the middle of the Pacific Ocean a kind of odd daily date situation occurs. For 2 hours every day, between 10:00 and 11:59 UTC, there exist 3 different weekdays concurrently. For example at UTC time Tuesday 10:15, it is Monday 23:15 in American Samoa, which is 11 hours behind UTC, and it is Wednesday 00:15 in Kiritimati, which is 14 hours ahead of UTC. For the first hour (UTC 10:00ľ10:59), this is true for inhabited territories, whereas during the second hour (UTC 11:00ľ11:59) it is only true if you count the uninhabited maritime time zone 12 hours behind UTC.

    About the "International Date Line" tour: Take a tour from the north pole to the south pole mainly across the enormous pacific ocean. Note the difference on certain parts of the line between the anti meridian and the agreed International Date Line (IDL). The direct distance along the anti meridian from the north to the south pole is roughly 20000 kilometers (12400 miles). If you follow the current agreed IDL it will extend the distance to about 30000 kilometers (18600 miles). This tour will give you a best bid of the placemarks from north to south of where, from east to west and reverse, to set your current date. This tour also outline, around the globe, tracks/path of the five major circles of latitude, the Arctic Circle, Tropic of Cancer, Equator, Tropic of Capricorn and Antarctic Circle and of course the Prime Meridian and the Anti Meridian. You can also find an illustration of the historic date line changes over time as well as the marking of the old and modern prime meridian at the Royal Greenwich Observatory. Tour creator: Tom Kjeldsen, created September 2009. Recommended to be viewed as a 'Play tour' in Google Earth with terrain feature enabled.

    Last edited by T.Dooley; 12-30-2011 at 09:54 AM.

  2. #2
    Google Earth Explorer T.Dooley's Avatar
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    It feels like a bit strange coincidence that this series of placemarks were submitted almost same time as the earthquake/tsunami hit apparently especially Samoa and Tonga, very close and central to the international date line, in the pacific ocean.

    Best wishes and hope to and for all in the area
    Last edited by T.Dooley; 10-01-2009 at 01:52 AM.
    Are you uptight, get downloose! Why not try a GE file - Also downloadable at GEC and http://ge.dooley.dk - Tom Kjeldsen


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    Member avrilismymom's Avatar
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    Wink Random Time Travel Distortions

    Quote Originally Posted by T.Dooley View Post
    The effect of ignoring the date line is also seen in Jules Verne's book "Around the World in Eighty Days", in which the travelers, led by Phileas Fogg, 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 traveled the direction opposite to the one taken by Magellan, they believe the date there to be one day later than it truly is.
    I saw the movie version of this about two weeks ago, the one with Jackie Chan in it. And as proved/mentioned/whatever above, they thought they had lost the bet but they crossed the date line making them winners instead.

    Reminds me of the one time where I flew in an airplane from one time zone to the next. The plane took off at 7:35 and landed at 7:20 (or 19:35 and 19:20 if you use the 24-hour system).

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    Google Earth Explorer T.Dooley's Avatar
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    Quote Originally Posted by avrilismymom View Post
    Reminds me of the one time where I flew in an airplane from one time zone to the next. The plane took off at 7:35 and landed at 7:20 (or 19:35 and 19:20 if you use the 24-hour system).
    Sure this 'time travel' is a bit odd and I personally see it as a bit facinating that this 'problem of date and time' mainly occur because we are able of travelling so fast that we can cross a date line within the limits of 'one date' a day.

    I believe you would not care very much if you had to sail the 1000 kilometers / 555 nautical miles from Tonga to Samoa with an average speed of 5 knots (nm/hour) taking you 111 hours or 4,5 days to reach your destination.

    Nowadays this can be done a few hours, bringing you back in time from sunday 1 am to the previous friday 10 pm, while you sit 3 hours in a plane eating snacks.

    It becomes even more hard to cope with (believe me) when you take a plane from europe to america and step something like 6-9 hours back in time and when returning forward again. Have never tried crossing the date line but this must be even more confusing with great distances like Fiji to California, taking you from Friday 7:23 a.m. in Fiji to Thursday 11:23 a.m. in Los Angeles!

    PS. up till this day I would anyday prefer a wormhole tour as long as the end point could be of a certain precision
    Last edited by T.Dooley; 10-02-2009 at 04:37 AM.
    Are you uptight, get downloose! Why not try a GE file - Also downloadable at GEC and http://ge.dooley.dk - Tom Kjeldsen


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    Google Earth Explorer T.Dooley's Avatar
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    Pacific Island Samoa has decided, 119 years after they moved towards east of the international date line, to move back west. As a day are added, by concept, moving east across the international date line, the day of December 30th 2011 will not exist in the area.

    News Source: http://www.samoaobserver.ws/index.ph...tent&Itemid=85

    Also Tokelau has decided to move across the date line or more correct move the date line to the east of the islands, along with Samoa.

    News Source: http://www.rnzi.com/pages/news.php?op=read&id=63444

    The date line has just moved! Today, as this is written, the 30th of December 2011 does not officially exist at the Samoa and Tokelau islands since the international date line (IDL) now has moved aproximately 200 kilometers, 125 miles to the east for the part of the IDL around these Islands. This happend at 10:00 (10 a.m.) UTC/GMT time when the islands passed midnight and calendar switched from 29th to the 31th of December 2011.









    As a kind of natural spin off of this actual relocation of the international date line, the "Date Line tour (http://www.gearthhacks.com/dlfile33073/Date-Line.htm
    )" has been updated accordingly and also added additional historical date line courses. Wish you all a nice "date" (even if you don't have one) today and onward :-)
    Last edited by T.Dooley; 12-30-2011 at 03:55 PM.
    Are you uptight, get downloose! Why not try a GE file - Also downloadable at GEC and http://ge.dooley.dk - Tom Kjeldsen


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