Motions of the earth
a) Earth’s axis: An imaginary line joining north and south poles is called earth’s axis.
b) Inclination: The earth is tilted at an angle of 23 1/2o. This tilt is called inclination.
c) Circle of illumination: The imaginary line that divides the surface of the earth into day and night is called Circle of illumination.
d) Perihelion: When the distance between the Sun and the Earth is minimum ie 147 million km on January 4 then it is called Perihelion.
e) Aphelion: When the distance between the Sun and the Earth is maximum ie 152 million km on July 4 then it is called Aphelion.
f) Earth Day: The earth takes 24 hours to complete one rotation, thus the time taken by the earth is called the Earth Day or the Solar Day.
g) Oblate Spheroid: Rotation causes bulging of the earth near the equator and flattens the poles .This shape of the earth is called Oblate Spheroid.
Q2) Answer the following:
What are the effects of rotation?
Ans: The effects of rotation are:
a) It causes day and nights in alternate pattern at all places on the surface of the earth.
b) High tides and low tides occur twice in a day due to rotation.
c) Deflection of wind or ocean currents takes place. The deflection takes place towards its right in the northern hemisphere and towards its left in the southern hemisphere.
d) Rotation causes bulging of the earth near the equator and flattens the poles . This is called Oblate spheroid.
e) The sun rises in the east and sets in the east
Q3) a) Draw the circle of illumination figure 4.1 on page no 34. Label the earth’s axis and the circle of illumination.
b) Draw the fig. 4.2 on page 35 perihelion and aphelion