The International Date Line (IDL) is an imaginary line on the surface of the Earth, that runs from the north to the south pole and demarcates one calendar day from the next. It passes through the middle of the Pacific Ocean, roughly following the 180° longitude but it deviates to pass around some territories and island groups.
The International Date line is on the opposite side of the Earth to the Prime Meridian. The Prime Meridian helps to define Universal Time and is the meridian from which all other time zones are calculated. Time zones to the east of the Prime Meridian are in advance of UTC (up to UTC+14); time zones to the west are behind UTC (to UTC-12).
Mostly, the International Date Line and the moving point of midnight separate the two calendar days that are current somewhere on Earth. However, during a two-hour period between 10:00 and 11:59 (UTC) each day, three different calendar days are in use. This is because of daylight saving in the UTC+12 zone and the use of additional date-shifted time zones in areas east of the 180th meridian. These additional time zones prevent the earth from observing a single date for the instant when midnight crosses the IDL. It also results in the standard time and date in some communities being 24 or 25 hours different from the standard time and date in others.
A traveler crossing the International Date Line eastbound subtracts one day, or 24 hours, so that the calendar date to the west of the line is repeated. Crossing the IDL westbound results in 24 hours being added, advancing the calendar date by one day. The International Date Line is necessary to have a fixed, albeit arbitrary, boundary on the globe where the calendar date advances in the westbound direction.
Read more about International Date Line: Geography, De Facto and De Jure Date Lines
Famous quotes containing the words date and/or line:
“Until I was twenty-five, I had no development at all. From my twenty-fifth year I date my life. Three weeks have scarcely passed, at any time between then and now, that I have not unfolded within myself. But I feel that I am now come to the inmost leaf of the bulb, and that shortly the flower must fall to the mould.”
—Herman Melville (1819–1891)
“The line that I am urging as today’s conventional wisdom is not a denial of consciousness. It is often called, with more reason, a repudiation of mind. It is indeed a repudiation of mind as a second substance, over and above body. It can be described less harshly as an identification of mind with some of the faculties, states, and activities of the body. Mental states and events are a special subclass of the states and events of the human or animal body.”
—Willard Van Orman Quine (b. 1908)