Careers in the maritime industry
December 11, 2015
International time zones
October 12, 2015
Show all
0

10_1_3_International_Date_Line_03

The International Date Line (Date Line) is one of the strangest aspects of a study of time zones. Although it follows the general course along the 180O Line of Longitude, it does not run through any country, but runs only through the ocean in that area. As it avoids passing through any land to avoid confusion, it is not a straight line.

  • The officer on watch when a ship crosses the Date Line on a voyage from Japan to San Francisco at 10:30 on Tuesday 4 March will have to change the ship’s time to read 10:30 on Monday 3 March!
  • The officer on a ship steaming in the other direction and crossing the Date Line at 06:45 on Thursday 6 March will have to change the ship’s time to read 06:45 on Friday 7 March.
  • If you are on a ship sailing from New Zealand to San Francisco and it is 21:00 (9 pm) on your birthday when the ship crosses the Date Line, you will repeat most of your birthday! (As the ship crosses the Date Line, the time will change to 21:00 on the previous day. You can have another birthday!)
  • If your ship is steaming the other way from San Francisco to New Zealand, and it is 06:00 (6 am) on your birthday when the ship crosses the Date Line, you will miss most of your birthday! (As the ship crosses the Date Line, the time will change to 06:00 on the next day, and you will loose part of your birthday from 06:00 to midnight!)
  • In summary :
    A ship going from west to east (e.g. from New Zealand to Chile) will repeat 24 hours.
    A ship going from east to west (e.g. from the west coast of Canada to China) will lose 24 hours.

Now you can see why the International Date Line does not run through a country – it would be one day on the eastern side of the International Date Line and the next day on the western side! Imagine the confusion if a country operated like that!

Test Yourself : International Date Line

1. A ship is steaming from Chile (west coast South America) to Australia and just before she crosses the International Date Line, the officer of the watch notices that the time is 01:00 (1 am) on Tuesday 24 July. What will be the time, day and date when the ship has crossed?

2. Which of these ships will cross the International Date Line?

2.1.  A ship steaming from Sydney (Australia) to Singapore

2.2.  A ship steaming from Sydney to Shanghai (China)

2.3.  A ship steaming from Shanghai to Panama Canal

2.4.  A ship steaming from Panama Canal to New York

2.5.  A ship steaming from Singapore to Vancouver (Canada)

3.  For each of the ships mentioned in Question 2 above that will cross the International Date Line, write down whether she will repeat 24 hours or lose 24 hours.