The international dateline is an imaginary boundary that runs vertically from the North pole to the south pole acting as a universal indicator to commence and end a calendar day. This imaginary line geographically is located in the pacific ocean. The International Dateline passes at 180-degree longitude deviating to pass around some territories and island groups. The line itself is not completely linear as there are some countries that are in the Western hemisphere and some fall in the Eastern Hemisphere as the line passes through some island countries.
If you observe the above images you will notice in the first image the IDL is at the extreme left side at around 180 degrees and is not exactly a straight line. Similarly in image 2 of the globe, the line is not a straight line.
Why Does the IDL pass through the middle of the Pacific Ocean and not via some other country?
Many people may be curious as to why does the IDL is set in the middle of the pacific ocean and not somewhere else as the earth is spherical in shape. The answer to that is simple since the prime meridian or zero degrees longitude passes through Greenwich UK and earth being a globe 180 degrees from either of the sides east or west lies in the pacific ocean. Supposing if the meridian had passed through any other country the time zones would have varied accordingly.
How does IDL affect travelers?
As all countries on the east of prime meridian would be ahead of time and all countries on the west of meridian would be behind the time of meridian the countries which are near to the Pacific on the left side of the line like Japan, Newzeland commence a day and countries to the right side of the line like the Hawai islands and other small pacific islands to the right side of the IDL will end the same calendar day. As such when a traveler from Japan when traveling to the USA which is on the other side of the line actually gains a day in travel.
Case 1 – The Curious Case of Mr. Lee’s travel from Hong Kong to Los Angeles USA.
Mr. Lee a resident of Hong Kong has booked his flight with Cathay Pacific airline from Hong Kong to LA. Cathay operates a non-stop service between two cities and flight leaves at 1215 am on the 1st of October from hong kong. Before Boarding the flight Mr. Lee checks all the details and notices the duration of the flight is 12hrs and 20 min and arrival time in LA will be 2035 (835pm), However, upon arrival, he checks with airline staff the time and date to adjust his clock and is advised that it was 835pm on 30th of September and not 1st of October he has reached a day earlier from when he had departed. Mr. Lee thinks about how is this possible since he clearly remembers he had departed on the 1st of October. Did Cathay Pacific airline passed through a wormhole or was it time travel. Where did the 12hrs 20 min vanish?
Here is the logical explain how this works?
Although Mr. Lee or Cathay did not technically travel ahead in time however they crossed something called an International Dateline. Hongkong is in Asia and is 8hrs ahead (+8) of GMT/UTC as per our time zones and Los Angles is in the USA (-8) behind Behind GMT/UTC. When the flight departed at 1215 am on 1st of October from Hongkong the time in GMT zone or Greenwich UK was 8hrs behind that means it was 415pm on the 30th of September and Los Angles is -8 hrs behind the GMT/UTC which means the local time LA when flight departed was 815am on 30th of September. So if you do the math and add 8 + 8 = 16 means Hongkong is 16hrs ahead of LA. The flight duration is 12hrs and 20 min.
16 hrs (time difference between HKG and LAX) minus 12 hrs 20 min (flight duration) = 3hrs 40 min (spare time)
So if the time difference between the two cities is 16hrs and flight duration is 12hrs 20 min Mr. Lee still had spare time when he landed in LA hence this spare time was adjusted (deducted) and he reached 3hrs 40 min earlier from when he departed.
The Flight departing time from Hongkong was 1215 am minus – spare time 3hrs 40 min = 835pm day before.
After a month or so Mr..Lee decided to come back to his home country. He loved his time in LA and was happy that he saved a day of his travel. He decided to take a flight with Cathay Pacific since he enjoyed their service and he reached way before he departed. He booked a ticket on CX 883 departing on 04th of November at 2330 (1130pm) and boarded his flight on schedule. He checked all the details and flight duration was 15hrs and 15min. By his calculations he would be reaching the next day in Hong Kong at around 1425hrs afternoon. But when he reached Hong Kong, it was Deja vu for him all over again. He checked with the airline staff and it was 0545am he was happy he reached earlier but then the airline staff advise it was06th of November and to his shock he realized he skipped an entire day. The reason how this happened can be explained as below.
How was this possible?
This is possible only because of IDL. The last time Mr. Lee traveled from Hong Kong to LA he traveled from east of IDL to west of IDL this time round he traveled in the opposite direction from West to East.
The time when he departed from LA was 2330 (1130pm) and LA is (-8) 8hrs behind GMT and Hongkong (+8) is 8hrs ahead of GMT. In short, both these cities have a time difference of 16hrs between them.
Hence when it was 1130pm in LA Hongkong was 16hrs ahead. This means 1130pm + 16hrs = 1530 or (330pm) so technically when he departed from LA it was already 5th of November 330pm in Hongkong and when we add travel time (flight duration) of 15hrs 15 min to that we get as below.
1530 + 15hrs and 15min = 0645am on 6th of November.
1530 + 30min + 1hr+1hr+1hr+ 1hr+1hr+1hr+ 1hr+1hr (8hrs30min out of 15hrs 15min of total travel time) = 12am or next 6th November still 6hrs 45min are added which becomes 0645am.
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