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                                     SAI  INTERNATIONAL SCHOOL

                                               SESSION 2020-21
                                                    GRADE  -VI
                                                   GEOGRAPHY

                           CH-2 GLOBE:LATITUDES AND LONGITUDES



               SUB –TOPIC : LONGITUDES AND TIME , STANDARD TIME
               NOTES:
               How to measure time?


                      In Earlier days people could measure time by seeing the movement of
                       Earth, moon and planets.
                     The Sun daily rises in the Eastern sky and sets in Western sky.
                     Sun is the best time keeper throughout world.
                     People can know about time by seeing the shadow cast by Sun.
                     It is shortest at noon and longest at Sunrise and Sunset.

               RELATION OF LONGITUDE AND TIME:
                     Counting of time starts from 0 degree Prime Meridian at Greenwich near
                       London.
                     As Earth rotates from West to East, places East of Greenwich will be
                       ahead of it’s time.
                     Places West of Greenwich will be behind it’s time.
                     Earth rotates 360 degree in 24 hours.
                     360divided by 24 hours= 15 degree
                     Earth rotates 15 degree in 1 hour.
                     Earth rotates 1 degree in 60/ 15 =4 minutes
                   Hence ,there will be difference of time of 4 minutes between two
                   consecutive longitudes.
                Eg:If Greenwich time is = 10 o’ clock
                      15 degree East of Greenwich time= 10+1 =11 o’clock
                    While 15 degree West of Greenwich time= 10-1 = 9 o’clock

               LOCAL TIME:
               When Sun is at the highest point in the sky and  casts  shortest shadow, that
               time can be adjusted to 12 o’clock and all places in the given meridian will
               have same time which is known as the local time of that meridian of longitude.

               STANDARD TIME:  The local time of places that lie on different meridians
               differ. It is, therefore, necessary to adopt the local time of some central
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