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Lesson Longitude and Time
6.1

FACTS The longitude that passes through Greenwich
to Understand observatory near London is known as Prime
Meridian or Greenwich Meridian and the standard
time taken is called Greenwich Mean Time (GMT).

Longitude and Latitude of the earth

Longitudes are the imaginary lines on the earth that run vertically spreading north
to south in a semi-circular way. The lines are the angular distance from east to west
in the earth. The line of latitudes are usually expressed in the degrees and denoted
by the Greek letter Lamda (λ). The prime meridian, which passes through the Royal
Observatory of Greenwich, England is intended to establish the position of zero degree
longitude. The longitude of the other places was to be measured as the angle east or
west from the Prime Meridian, ranging from 0° at the meridian to +180° eastward
and-180° westward. Thus, in each of the eastern and the western hemisphere, there
are total of 360°.

Longitudes are related to time or it determines time. As the longitude varies the time
of such place is different. For example, when it is 12 noon in Nepal, it is midnight in
Illinois in the USA.

As the earth rotates around its axis from west to east, it takes 24 hours to complete
one rotation. It means, the earth covers the 40,076 km or angular distance of 360°.
This is called the rotation of the earth. This shows that earth completes its 360°
rotation in 24 hours, 15° = 1 hour and 1° = 4 minutes. As the sun rises in the east and
sets in the west. So every 1° east ward the time is 4 minutes ahead because the earth
moves from west to east.

Dynamic Social Studies - Book IX 188