### 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 the 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.
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 -  You lose a day
From the East to West - You Gain a day
• Based on this, the date is fixed for different countries or regions of the world.
• This is not a straight line.
• Incase, if the line is drawn straight, two places in the same country will have different dates.
• In order to avoid this confusion, the International Date Line is found zigzag in few places.