4. The movement of the earth
around the sun along a fixed
path is called Revolution.
5. Effect of revolution
Variation in the length of days and
nights.
Distribution of heat over the Earth.
Occurrence of seasons
6. Variation in the length of days and nights
The earth is tilted. As the earth revolves around
the sun it rotates on its axis, on it's tilt. This
causes different sides of the the planet to get
different amounts of sunlight. In summer the
days are longer than nights while in winter the
nights are longer. At the poles the variation is
maximum.
8. • The part of the Earth that has tilted toward the sun
receives vertical rays of the Sun while the other part
receives slanting rays. Vertical rays give more heat
than slanting rays. The Equator and the regions near
it always receive the vertical rays of the Sun. As we
move away from the Equator, the sun’s rays become
slanting and the amount of heat received, also
decreases.
10. Seasons
The Earth's seasons are not caused by the differences in the
distance from the Sun throughout the year (these differences
are extremely small). The seasons are the result of the tilt of
the Earth's axis.
The Earth's axis is tilted from perpendicular to the plane of the
ecliptic by 23.45°. This tilting is what gives us the four seasons
of the year - spring, summer, autumn (fall) and winter. Since the
axis is tilted, different parts of the globe are oriented towards
the Sun at different times of the year.
