Chapter Notes: Motions of the Earth

# Chapter Notes: Motions of the Earth - Notes | Study Social Studies (SST) Class 6 - Class 6

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The Earth has two types of motions namely, rotation and revolution.

Rotation of Earth

Rotation is the movement of the earth on its axis.

Rotation and revolution of earth

• Days and Nights take place because of rotation.
• The axis of the earth which is an imaginary line, has an angle of  66.5°  with its orbital plane.
• The circle that divides the day from night on the globe is called the circle of illumination.

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.

Question for Chapter Notes: Motions of the Earth
Try yourself:Motion of the earth on its axis in about 24 hours is called __________

Revolution of Earth

The second motion of the earth around the sun in its orbit is called revolution.

Revolution of Earth and change of seasons

• Revolution is the movement of the earth around the Sun in a fixed path or orbit. Revolution causes the change of seasons.
• It takes 365 days and 6 hours (one year) to revolve around the sun.
Leap Year
• We consider a year as consisting of 365 days only and ignore six hours for the sake of convenience.
• Six hours saved every year are likely to make one day (24hours) over a span of four years.
• This surplus day is added to the month of February.
• Every fourth year, February is of 29 days instead of 28 days. This year with 366 days is called a leap year.
Summer and Winter Solstice
• The earth goes around the sun in an elliptical orbit.
• The nights are longer than the days in the winter season. This position of the earth is called summer solstice.
• On 22nd December the Tropic of Capricorn gets direct rays of the sun as the South Pole tilts towards it. It is summer in the Southern hemisphere and winter in the Northern hemisphere. This is called the winter solstice.
• On 21st March and 23rd September, direct rays of the sun fall directly on the equator. During this period, the whole earth experiences equal days and equal nights. This is called an equinox.

Question for Chapter Notes: Motions of the Earth
Try yourself:Why do seasons change on the earth?

Q.1: Define rotation and revolution of the Earth.
Ans: Rotation: Movement of the Earth on its axis in nearly 24 hours is termed as rotation. It is also called the daily movement of the earth.

Revolution: Movement of the earth around the Sun on a fixed path or orbit is called revolution.

Q.2: What is the circle of illumination? Why does it not coincide with the axis of the Earth?
Ans: The circle which separates day from night is called the circle of illumination. This circle does not coincide with the axis because of the inclination of the axis by 2314° towards east.

Q.3: Distinguish between rotation and revolution.
Ans: The distinction between rotation and revolution is as under:

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