Explanation:
As you know that the earth has two types of motions,
namely rotation and revolution. Rotation is the
movement of the earth on its axis. The movement of
the earth around the sun in a fixed path or orbit is
called Revolution.
The axis of the earth which is an imaginary line,
makes an angle of 66½° with its orbital plane. The
plane formed by the orbit is known as the orbital plane.
The earth receives light from the sun. Due to the
spherical shape of the earth, only half of it gets light
from the sun at a time (Figure 3.2). The portion facing
the sun experiences day while the other half away from
the sun experiences night. The circle that divides the
day from night on the globe is called the circle of
illumination. This circle does not coincide with the
axis as you see in the Figure 3.2. The earth takes about
24 hours to complete one rotation around its axis.
The period of rotation is known as the earthday. This is
the daily motion of the earth.
2021–22
MOTIONS OF THE EARTH 19
Figure 3.3 : Revolution of the Earth and Seasons
What would happen if the earth did not rotate? The
portion of the earth facing the sun would always
experience day, thus bringing continuous warmth to
the region. The other half would remain in darkness
and be freezing cold all the time. Life would not have
been possible in such extreme conditions.
