The document discusses the motions of the Earth that cause day and night and seasons. It explains that the Earth rotates on its axis once every 24 hours, causing day and night. It also revolves around the Sun once every 365.25 days. The Earth's axis is tilted at an angle of 23.5 degrees, which causes the seasons as different parts of the Earth receive more or less direct sunlight throughout the year. The solstices mark the longest and shortest days of the year when the sun's rays are most direct, while the equinoxes have equal hours of daylight and darkness.

1. Motions of the earth

2. Learning objectives
• Rotation of the earth
• The earth’s axis
• Inclination of the earth’s
axis
• Orbital plane
• Circle of illumination
• Revolution of the earth
• Leap year
• Summer and winter
solstice
• Equinox

3. Rotation
• The movement of the
earth on its axis is called
rotation
• The earth takes 24 hours
to rotate on its axis once,
which is called as Earth
day

4. Axis
• The imaginary line on
which the earth spins.
• It passes through the
north pole ,centre & south
pole of the earth.
• The axis is tilted at an
angle of 66 ½ degree to
the orbital plane

5. Orbit and Orbital Plane
Orbit- The path taken by the
planets to go around the Sun
is known as the orbit
Orbital plane - The plane in
which its orbit lies.

6. Tilt of the axis
• The earth’s axis is tilted at
an angle of 66 ½ degree
with its orbital plane,
which is 23 ½ degree to
the perpendicular line
from the elliptical plane

7. Rotation causes Day and Night
• The part of the earth facing the sun has day and
the part of the sun which does not receive
sunlight has night
• If the earth doesn’t rotate, the portion of the
earth facing the sun would experience day time
and the other half would experience night time
permanently
• They would experience continuous warmth and
freezing cold temperatures .Life would not be
possible in such extreme conditions.

8. Circle of illumination
• The imaginary line which
divides the parts of the
earth with day and night is
called the circle of
illumination.

9. Revolution
• Movement of the earth around the
sun on a fixed orbit is called
revolution
• The earth takes 365 ¼ days to
complete one revolution

11. Leap Year
• The earth takes 365 ¼ days to complete
one revolution
• We consider only 365 days for the sake of
convenience
• The other ¼ days( 6 hours) are added up
once in four years to make an extra day,
which is added to the month of February.
• Thus, once in four years, we have 366 days
in a year, with 29 days in February. This
year is called a leap year

12. Revolution causes seasons
Seasons are caused because of revolution of earth
around the sun and Earth’s tilted axis
There are four seasons – Spring, Summer, Autumn and
Winter

13. Solstices and Equinoxes
Seasons change due to the change in the
position of the earth around the sun.
Four important positions
• Spring Equinox – 21st March
• Summer Solstice- 21st June
• Autumn Equinox- 23rd September
• Winter Solstice – 22nd December

14. Summer Solstice- 21st June
• Northern hemisphere is tilted towards the
sun and the southern hemisphere is tilted
away from the sun
• The sun rays fall directly on the tropic of
cancer
• The places around north pole receive
continuous daylight for six months
• It is summer in the northern hemisphere
and winter in the southern hemisphere
• 21st June is the longest day and the
shortest night of the year in the northern
hemisphere

15. Winter Solstice- 22nd December
• Southern hemisphere is tilted towards
the sun and the northern hemisphere is
tilted away from the sun
• The sun rays fall directly on the Tropic of
Capricorn
• The places around south pole receive
continuous daylight for six months
• It is summer in the southern hemisphere
and winter in the northern hemisphere
• 21st / 22nd December is the longest day
and the shortest night of the year in the
southern hemisphere

16. Equinoxes
• The equinoxes happen in March (about
March 21) and September (about
September 23). These are the days when
the Sun is exactly above the Equator,
which makes day and night of equal
length.
• In the Northern Hemisphere,
• 23rd September - Autumn
• 21st March- Spring