Page 42 - Geography for Secondary Schools Student’s Book Form One

Geography for Secondary Schools
Student’s Book Form One

(b) Longitudes are used to calculate local (ii) When calculating time of two places
time of different places on the earth’s located on the same side of the prime
surface. meridian, for example, East to East

(c) They enable us to precisely identify or West to West, you should find the
any location on the Earth. difference in degrees by subtracting
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(d) They enable us to identify routes for the degrees of the two places.
aviation and navigation. (iii) When calculating the time between
(e) They help in forming a grid two places located in different sides
of the prime meridian, one on the East
system essential for mapping, and and the other on the West, you should
communication of geographic data add the degree of the two places. This
worldwide. is due to the rotation of the Earth on its
(f) Longitudes are used to determine days axis. The more you move towards the
and dates in the world with reference East, the more time increases, while
to the International Date Line. the more you move towards the West

(g) They help to determine distances the more time decreases. The time
between places on the earth’s surface. recorded along the same longitude is
known as Local Mean Time (LMT).
Consider the following examples.
Calculating local time using longitudes

The Earth rotates on its own axis from Example 1
West to East once after every twenty four The local time of Tunis located at 10°E is
hours (one day). This means that the Earth 03:00 pm. What is the local time of Mtwara,
turns through 360° in 24 hours. It rotates Tanzania located at 40° E?
15° in one hour or 1° in 4 minutes. All the Given
places along the same longitude experience
mid-day at the same time. For example, if Longitude Time
it is 12:00 noon in Addis Ababa (39° E), it Tunis (10° E) 03:00 pm
will also be 12:00 noon in Dar es Salaam Mtwara (40° E) Required
as it is also located at 39° E. On the
contrary, places along different longitudes Solution
experience different times. For example, (i) The difference in degrees of longitude
when it is 12:00 noon at places like Accra between Tunis and Mtwara will be:
in Ghana or London in England located
along the Greenwich meridian (0°), it will 40º – 10º = 30º
be 1:00 pm at all places along longitude (ii) The difference in time between Tunis
15°E or 11:00 am along longitude 15°W. and Mtwara will be calculated as
While calculating time the following follows:
conditions should be observed; If 15º = 1 hour Then 30º =?
(i) In calculating time, we use longitudes Therefore, 30º × 1 hour = 2 hours
of given places. 15 o

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