Page 111 - SST Class 06

Motions of

the Earth 17

q About the two different motions of the earth-rotation and revolution.
q How rotation of the Earth causes day and night. q The different times of day due to rotation.
q Revolution and its effect in the formation of seasons.

The vertical line from the
Introduction tilt is 23½°. The Earth earth’s orbital plane The earth’s axis
N.P.
When you travel in a train. You can see that all makes an angle of
buildings, trees and poles are running in the 66½° with its orbital 23½ °
opposite direction while your train appears to be plane. By orbital plane 66½° Tropic of Ca ncer
stationary. The same is the case with the Earth. The is meant the plane The plane
of the
E qua earth’s orbit
spinning of the Earth on its axis is called rotation formed by its orbit T o r pic o f tor
and its going round the Sun is called revolution . round the Sun. C pr
a icorn
The Earth is spherical S.P.
IMPORTANCE OF THE EARTH MOTIONS and at one time it Inclination of the Earth’s
receives sunlight on half axis and its orbital plane
Suppose, the Earth was not rotating and revolving,
of its part. The one-half part that receives sunlight
then its same side would face the Sun at all times.
It would mean that one-half of the Earth would at any one time experiences the day; while the
receive sunlight continuously and the other half other half which is in dark experiences the night.
would not receive any sunlight. It would be a
Info Bits
continuous day in one half and a continuous night Info Bits
in the other half and both these will have extreme
temperatures—one very hot and the other very The speed of rotation at the Equator is 1,600 km
cold. Life would be quite impossible in such a per hour.
situation. Thus, rotation and revolution of the Due to the Earth’s tilt at its axis, the phenomenon
Earth are important for us, as they cause day, night of day and night does not coincide with its axis. It
and seasons. means that when the North Pole is in sunlight, the

South Pole is in dark; and when the South Pole is
Just Think! in sunlight, the North Pole is in dark.

Do rotation and revolution of the Earth have any F ind Outind Out
effect on us?
What is calendar year?
ROTATION Day and Night

The Earth rotates on its axis like a top. Its axis is As the Earth turns west to east, the area under
formed by the two points—one on the top called sunlight keeps shifting. The area which comes
the North Pole and the other on the bottom called under sunlight experiences morning, while the
the South Pole. As you have seen that a globe is area which comes under dark experiences night.
tilted on its axis, so is the case with the Earth. This As the area shifts, the day rises or sets.
Motions of the Earth
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