Theory:

Greenwich Meridian
  • The Royal Astronomical Observatory is situated at Greenwich near London in England.
  • At the International Meridian Conference held in 1884 in Washington DC in the U.S.A. all nations unanimously agreed on choosing the Greenwich Meridian as the international standard meridian (0°).
  • This 0° line of longitude is called the Prime Meridian.
  • It is also called as the Greenwich Meridian as it passes through Greenwich.
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International Date Line
  • The 180° line of longitude has been established as the International Date Line.
  • It is drawn on the Pacific Ocean between Alaska and Russia through Bering Strait.
Important!
On crossing, this line
from the West to East loses a day
From the East to West Gains a day
  • Based on this, the date is fixed for different countries or regions of the world.
  • This is not a straight line.
  • Suppose if the line is drawn straight, two places in the same country will have different dates.
  • In order to avoid confusion, the International Date Line is found zigzag.