Globes may be of varying size and type – big ones,
which cannot be carried easily, small pocket globes,
and globe-like balloons, which can be inflated and are
handy and carried with ease. The globe is not fixed. It
can be rotated the same way as a top spin or a potter’s
wheel is rotated. On the globe, countries, continents
and oceans are shown in their correct size.
It is difficult to describe the location of a point on a
sphere like the earth. Now the question arises as to
how to locate a place on it? We need certain points of
reference and lines to find out the location of places.
You will notice that a needle is fixed through the
globe in a tilted manner, which is called its
axis
points on the globe through which the needle passes
are two poles – North Pole and South Pole. The globe
can be moved around this needle from west to east
just as the earth moves. But, remember there is a major
difference. The real earth has no such needle. It moves
around its axis, which is an imaginary line.
Another imaginary line running on the globe divides
it into two equal parts. This line is known as the
equator
. The northern half of the earth is known as
the Northern Hemisphere and the southern half is
known as the Southern Hemisphere. They are both
equal halves. Therefore, the equator is an
imaginary circular line and is a very
important reference point to locate places
on the earth. All parallel circles from the
equator up to the poles are called
parallels
of latitudes
. Latitudes are measured in
degrees.
The equator represents the zero degree
latitude. Since the distance from the
equator to either of the poles is one-fourth
of a circle round the earth, it will measure
¼
th of 360 degrees, i.e. 90°. Thus, 90
degrees north latitude marks the North
Pole and 90 degrees south latitude marks
the South Pole.
As such, all parallels north of the
equator are called ‘north latitudes.’
Similarly all parallels south of the equator are called
‘south latitudes.’
The value of each latitude is, therefore, followed by
either the word north or south. Generally, this is
indicated by the letter ‘N’ or ‘S’. For example, both
Chandrapur in Maharashtra (India) and Belo
Horizonte in Brazil (South America) are located on
parallels of about 20° latitude. But the former is 20°
north of the equator and the latter is 20° south of it.
We, therefore, say that Chandrapur is
situated at 20° N latitude and Belo
Horizonte is situated at 20° S latitude.
We see in Figure 2.2 that as we move
away from the equator, the size of the
parallels of latitude decreases.
I
MPORTANT PARALLELS OF LATITUDES
Besides the equator (0°), the North Pole
(90°N) and the South Pole (90° S), there
are four important parallels of latitudes–
(i)
Tropic of Cancer (23½° N) in the
Northern Hemisphere. (ii)
Tropic of
Capricorn
(23½° S) in the Southern
Hemisphere. (iii)
Arctic Circle at 66½°
north of the equator. (iv)
AntarcticCircle at 66½° south of the equator.
H
EAT ZONES OF THE EARTH
The mid-day sun is exactly overhead at
least once a year on all latitudes in
between the Tropic of Cancer and the
Tropic of Capricorn. This area, therefore,
receives the maximum heat and is called
the
Torrid Zone.
The mid-day sun never shines
overhead on any latitude beyond the
Tropic of Cancer and the Tropic of
Capricorn. The angle of the sun’s rays
goes on decreasing towards the poles. As
such, the areas bounded by the Tropic
of Cancer and the Arctic Circle in the
Northern Hemisphere, and the Tropic of
Capricorn and the Antarctic Circle in the
Southern Hemisphere, have moderate
temperatures. These are, therefore, called
Temperate Zones
.
Areas lying between the Arctic Circle
and the North Pole in the Northern
Hemisphere and the Antarctic Circle and
the South Pole in the Southern
Hemisphere, are very cold. It is because
here the sun does not rise much above
the horizon. Therefore, its rays are
always slanting. These are, therefore,
called Frigid Zones.
W
HAT ARE LONGITUDES?
To fix the position of a place, it is
necessary to know something more
than the latitude of that place. You
can see, for example, that Hyderabad
(in Pakistan) and Allahabad (in India)
are situated on the same latitude (i.e.,
25°25
'N). Now, in order to locate them
precisely, we must find out how far
east or west these places are from a
given line of reference running from
the North Pole to the South Pole.
These lines of references are called the
distances between them are measured in ‘degrees of
longitude.’ Each degree is further divided into minutes,
and minutes into seconds. They are semi-circles and
the distance between them decreases steadily polewards
until it becomes zero at the poles, where all the
meridians meet.meridians of longitude, and the
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