What is the International Date Line?

The international date line is an imaginary dateline on Earth�s surface defining the boundary between one day and the next. The history of the International Date Line dates back to the Christian era of 1522 when Magellan�s crew reached home after circumnavigating the world for the first time by ship. They thought it was 5th September but actually, they reached on 6th September.

The International Date Line is taken as 180o meridian. The line of longitude 180o is the same for East or West of the Prime Meridian. Since it is diametrically opposed to the Greenwich Meridian, it causes a time difference of a full day on crossing the line. What do you think, how does this work?

The time difference works out to 12 hours (180o x 4 min) from either side. Thus, on crossing the line, a day is added or subtracted. When crossing from the east, time will be 12 hours ahead and while crossing the line, the time will be 12 hours behind.

For example: If it is 8 PM Monday, 25th December at Greenwich, it will be 8 AM Tuesday, 26th December on crossing the 180o line. But if one has to travel from the west, it will be 12 hours behind or 8 AM Monday, 25th December. When the time lost or gained is computed together, the difference works out to full 24 hours and 180o E and W. Here, the difference between 8 AM, Monday 25th December and 8 AM, Tuesday 25th December is 24 hours.

The International Date Line is the 180o line. When crossing this line from west to east, a day is deducted or the time is fixed backward by one day. When crossing the International Date Line from east to west, a day is added, or the calendar is fixed one day ahead. The Dateline is a Zig-Zag line. What do you think, why is the line Zig-Zag not straight?

To avoid the confusion of having different dates within the same country, the Date Line bends and goes Zig Zag at the Bering Strait between Siberia and Alaska and at Fiji, Tonga, New Zealand, and some other Islands.

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