International Date Line is an imaginary line drawn through the Pacific Ocean which when crossed the calendar date changes by one date. It runs from North to South and divides the whole earth into two parts         . It is a point where a new day begins and ends. That is, where a complete rotation of the earth begins and ends. The International Date Line (I.D.L) is longitude 180° East and longitude 180° west. It is the longitude found opposite to the Greenwich meridian.

The I.D.L is zigzag in some parts to avoid landmasses. When crossing the I.D.L from West to East, a day is lost. When crossing it from East to West, a day is gained.

Great circles are imaginary lines that divide the Earth into two equal halves. All longitudes are great circles while only the equator is a great circle. This is because the length of all other latitudes reduces towards the poles.

IMPORTANCE OF GREAT CIRCLES

• They form the shortest distance between two places on the earth's surface.
• They help to reduce navigation time.
• They also help to reduce energy and cost.