Explain why we need the International Date Line.?

Question

Explain why we need the International Date Line.?

Answer 1

The first date-line problem occurred in association with the circumnavigation of the globe by Magellan's expedition (1519–1522). The surviving crew returned to a Spanish stopover sure of the day of the week, as attested by various carefully maintained sailing logs. Nevertheless, those on land insisted the day was different. Although now readily understandable, this phenomenon caused great excitement at the time!

The effect of ignoring the date line is also seen in Jules Verne's book Around the World in Eighty Days, in which the travelers, led by Phileas Fogg, return to London after a trip around the world, thinking that they have lost the bet that is the central premise of the story. Having travelled the direction opposite that taken by Magellan, they believe the date there to be one day later than it truly is.

Anyone traveling west and passing the line must add a day to what they would otherwise expect the date and time to be. Correspondingly, those going east must subtract a day. Magellan's crew and Verne's travelers neglected to make those respective adjustments.

Hope this helps!

Answer 2

Local time is exactly related to the sun being at its high point at noon.  This was inconvenient for railroads trying to publish schedules of arrival and would be awkward for everyone once automobiles became common, so the earth was divided into 24 zones about 15 degrees wide each keeping the same time and changing abruptly 1 hour at the boundry.  It was quickly realized that because the earth normally carries each of us through time as it turns, if a traveler was going around the earth one way met another traveler going the other way (or just got home) one subtracting an hour for each time zone, the other adding, they would disagree about the date.  So opposite Greenwich England fortunately out in the middle of the mostly empty Pacific a line was marked where, no matter what the time travelers have to add or subtract a day depending on direction.  

  If you think about it, the same thing happens at every boundry between time zones at midnight, but we think it is "natural" and sweeps right by every day.   Suppose you had a clock with a GPS that "knew" what time zone you were in and you traveled back and forth across the time zone boundry at about midnight.   Each time you traveled east, not only would the clock have to gain an hour, but the date would have to change to the next day; each time west, lose an hour and change the date back.