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5.2.
The Earth’s rotation
5.2.1.
Time zones
Because the Earth is a sphere, not all the areas of the planet receive sunlight at
the same time. As a result, the time of the day varies between some continents
and even between countries of the same continent or between cities in the same
country.
To unify time, in the 19
th
century, the Earth was divided into 24 meridians. These
are imaginary lines that go from pole to pole, in semicircles. Each area between
two meridians was called a
time zone
.
All the countries and cities that belonged to the same time zone had the same
time. Later, the time zones were changed so they were adjusted to borders of
countries or regions. This is why the borders of the time zones are so irregular.
Starting from the
Greenwich meridian (0º)
, an hour is added for each time zone
going east and an hour is subtracted going west. The calendar day starts at 180º
east meridian and ends at 180º west meridian.
The Earth takes 23 hours and 56 minutes to complete one rotation on its axis.
Rotation
causes
day
and
night
.
Time zones
Understand
24.
Is there a relation between
the length of a day and the
existence of leap years?
Analyse
25.
Find out if there is any
place on the Earth where
night or day lasts 24 hours.
Where andwhen does this
occur?
26.
If the Sun rises in the east,
what time is it in Madrid
when it’s 00:00 in Sidney?
27.
Where are there more
hours of daylight in
summer, in Spain or
England? And in winter?
Explain your answers.
Analyse
23.
Look at the diagram. The Earth rotates from west to east. Explain in your
own words why the Sun appears to move accross the sky from east to west.
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