| The International Date
Line
The International Date Line (IDL) is an imaginary
line on the surface of the Earth opposite the Prime Meridian. The IDL is
where the date changes as one travels east or west across it. Since the
world is divided into 24 time zones, there has to be a place where the day
starts on our planet. The IDL along the 180° line of longitude, exactly
one-half way around the planet from Greenwich, serves just that purpose.
Cross the line from the east to the west and a day is added ("losing" a
day). Cross from west to the east and a day is subtracted ("gaining" a
day). The exact number of hours lost or gained depends on the time zones.
Without the International Date Line, people
travelling west around the globe would discover upon return home that it
would seem as though an extra day has passed. This situation actually
happened to Magellan's crew when they returned home after their
circumnavigation of the earth.
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