What is the International Date Line (IDL)?
Q: What is the International Date Line (IDL)?
A: The International Date Line (IDL) is an imaginary line on the surface of the Earth that goes from north to south in the Pacific Ocean.
Q: How does the date change when you cross the International Date Line?
A: The date becomes one day later as one travels across it in western direction and one day earlier as one travels across it in eastern direction.
Q: What causes the time difference between the eastern and western sides of the International Date Line?
A: The time difference is caused by the fact that the countries on the western side of the International Date Line have the time zone 10–12 hours more than Greenwich, while the countries on the eastern side have the time zone 9–12 hours less than Greenwich.
Q: How much do you need to adjust your watch when crossing the International Date Line?
A: When travelling across the line, one's watch has to be adjusted 20–24 hours, depending on the time zones.
Q: Why do you need to adjust your watch when crossing the International Date Line?
A: You need to adjust your watch when crossing the International Date Line because the time zones on either side of the line are different.
Q: Can you give an example of the time difference between two countries on either side of the International Date Line?
A: Yes, for example, New Zealand is twelve hours ahead of Greenwich Mean Time while Hawaii is ten hours behind Greenwich Mean Time.
Q: How many hours do you need to adjust your watch if you travel from New Zealand to Hawaii?
A: If you travel from New Zealand to Hawaii, you need to adjust your watch 22 hours backwards, which is about one day.
