Page 44 - Geography for Secondary Schools Student’s Book Form One

Geography for Secondary Schools
Student’s Book Form One
Example 2 approximately 15 longitude apart. There
o
What is the longitude of Lindi whose local would be problems in telling time if every
time is 08:24 pm when the local time in place had its own time set according to the
Montevideo, Uruguay located at 56º W is Local Mean Time (LMT).
02:00 pm?
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Given Essence of time and time zones
Longitude Time The essence of time zones resulted
Montevideo-Uruguay 56° W 02:00 pm from difficulties in identifying time for
Lindi? 08:24 pm a particular area. If each place across a
country followed its own time, it would
Solution create confusion. For example, Dodoma is
(i) The difference in time between Lindi about 35 E and Tanga is about 39 E. If each
o
o
and Montevideo will be: followed its own local time, there would
08:24 – 02:00 = 06:24 hours. be a difference of 16 minutes between the

(ii) The difference in degrees of longitude two towns. There would be confusion in
between Lindi and Montevideo. railway and airways timetables or in radio

Convert the time into minutes programmes if they had different in times,
each referring to its local area.
6 hours and 24 minutes = 384 minutes

Since the Earth rotates 1 in 4 minutes. To avoid time confusion, different stretches
o
of land take their time from agreed meridian.
How many degrees will it take to
rotate 384 minutes? The time adopted is known as standard
time. In East Africa, standard time is taken
Difference in longitude from the meridian of 45°E. When the whole

384 min × 1 o = 96 o stretch of land keeps the same standard time
4 min and that stretch forms a time zone. The
Greenwich Meridian is the starting point
(iii) Since the time of Lindi is ahead of that for dividing the globe into 24 time zones.
of Montevideo, Lindi must be located The standard time for Greenwich is known
east of Montevideo. Therefore, the
longitude position of Lindi will be: as the Greenwich Mean Time (GMT).

96 – 56 = 40 E
o
o
o
Variation of standard time in a single
country
Time zones
Countries with large stretches of land,
A time zone refers to a stretch of land where for example, Russia, the United States of
the standard time is accepted throughout America, Canada and China have several
the longitudinal zone of 15 in width. The standard time zones for practical purposes
o
world is divided into 24 time zones, each (Figure 3.16).

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