Question by john: Does the international date line begin at the observatory in Greenwich or Ness Point?
Until today I was under the misconception that Greenwich, England demarcated one day from another by dividing the time zones. That as the international date line, standing to the west could place you into Tuesday evening, while standing to the east could mean you were in early Wednesday morning. However I just read that England has only one time zone and that Greenwich is inland from the eastern coast by about 80 miles. Does this mean that Greenwich is the international date line everywhere in the world except for the eastern coast of England? That seems a bit messy.
Best answer:
Answer by cymry3jones
In theory the international date line is situated 180° east of Greenwich. However, in order not to split some countries in half, it is not a straight north to south line. There a deviations.
International Date Line
The International Date Line sits on the 180º line of longitude in the middle of the Pacific Ocean, and is the imaginary line that separates two consecutive calendar days.
It is not a perfectly straight line and has been moved slightly over the years to accommodate needs of varied countries in the Pacific Ocean. Note how it bends to include all of Kiribati in the Eastern Hemisphere.
Immediately to the left of the International Date Line (the date) is always one day ahead of the date (or day) immediately to the right of the International Date Line in the Western Hemisphere.
On the time and date codes shown below, note that Tonga and Samoa have the same time but are (1) day apart, as Samoa is in the Western Hemisphere, on the opposite side of the International Dateline from Tonga. A global Earth view is here.
As you travel further west, note that the time in Fiji is (1) hour earlier than Tonga. You will also notice that Hawaii, further to the east of Samoa, is (1) hour later in time.
So, travel east across the International Date Line results in a day, or 24 hours being subtracted. Travel west across the International Date Line results in a day being added.
Is that clear?
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