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World Time Zones

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World Time Zones and Greenwich Mean Time

In the previous lesson, we knew that both latitudes and longitudes are used to locate places and countries precisely on the earth's surface.

There are altogether 360 longitudes on the earth, each representing a degree. The earth completes a rotation in a day i.e. 24 hours. This means it travels about 40000 km or 360° each day and each longitude in 4 minute difference from another nearest longitude. For convenient and practical international time relations, the earth in divided into 24 time zones with an interval of 15° that equals 1 hour. Following the establishment of the Royal Observatory Act at Greenwich in London in 1675, the longitude at Greenwich began to be used as their prime meridian by English cartographers. In 1884 a conference agreed to use this meridian as the prime meridian for all maps. Time zones are described as per their distance east or west of the prime meridian. As for this, every 15° eastward the time is 1 hour ahead because the earth moves west to east. Now the time was calculated in the base of GMT. It in mid-day (12:00 PM) at a place when the sun directly falls on its meridian. The shadow of an object in shortest at this moment of each day.

World-Time-Zone.jpg

International Date Line

date-line.jpg

The international date line passes along the 180° longitude, except on inhabited islands in the pacific. It marks the place where travelers change their their date by 1 day on their voyage. East of the line (Western hemisphere) it is the one day earlier than to the west (Eastern hemisphere). The date line in curved eastwards and westwards to avoid crossing the land so that time relations in the region would not be complicated. Ponder over the trouble it might create if the line crossed over a small island in the pacific ocean.



  • There are altogether 360 longitudes on the earth, each representing a degree.
  • Following the establishment of the Royal Observatory Act at Greenwich in London in 1675, the longitude at Greenwich began to be used as their prime meridian by English cartographers.
  • The international date line passes along the 180° longitude, except on inhabited islands in the pacific.
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Very Short Questions

As the question,

Madras at 80 degree EL is 3 p.m.

New York at 75 degree WL =?

The longitude of two places is (75 +180- 80)degree

=225 degree – 80 degree

=145 degree
In one degree longitude there will be 4 minutes.
In 145 longitude (145x 4) minutes i.e. 580 minutes.
580 minutes corresponds to 9 hours 40 minutes.
Therefore it will be 5:20 a.m.

New York lies at 75 degree EL

The difference of longitude of two places = (75 degree + 180 degree – 86 degree)

=255 degree-86 degree

=169 degree

In 1 degree longitude there will be 4 minutes.

In 169 degree longitude (169 degree x 4) there will be 676 minutes.

676 minutes or 11 hours 26 minutes

Therefore, If It’s 10 am in New York, as Nepal lie at EL. It is 100+ 11:26 = 21:26 P.M.

So, it will be 9:26 in Nepal.

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  • When was establishment of the Royal Observatory Act at Greenwich in London?

    1675 AD
    1776 AD
    1778 AD
    1877 AD
  • 150 equals

    4 hour
    3 hour
    2 hour
    1 hour
  • When does earth completes its one rotation?

    15 hour
    18 hour
    24 hour
    12 hour
  • When does earth completes its one revolution?

    3 year
    1 year
    2 year
    4 year
  • Season changes due to

    rotation
    revolution
    orbit
    axis
  • Day and night is due to

    axis
    orbit
    rotation
    revolution
  • An imaginary line of longitude on earth surface located at about 180 degrees of Greenwich meridian is

    Prime meridian line
    World time line
    International Date Line
    Hemisphere line
  • The time eastward is ______ and westward is______

    fast, slow
    equal
    none of the above
    slow, fast
  • The 24 world time zones (each representing 15 degree an hour) are described as per their

    Distances of prime meridian
    Distance of hemisphere lines
    Distance of equator lines
    Distance of world time
  • There are altogether ______latitude on earth each representing a degree

    240
    150
    360
    138
  • The earth completes a rotation in a day means it travels about

    19,000 km
    31,000 km
    40,000 km
    21,038 km
  • Every 15 degree eastward the time is one hour ahead because the earth moves

    East to west
    East to south
    West to east
    North to south
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