GEOGRAPHY (VI)-LESSON-3 MOTIONS OF THE EARTH (LESSON NOTES)

GEOGRAPHY (VI)-LESSON-3

MOTIONS OF THE EARTH

(LESSON NOTES)

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v INTRODUCTION:

 

Ø The Earth is a dynamic planet. It is called as blue planet. It has two motions:-

§  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.

v AXIS OF THE EARTH

 

Ø An imaginary line which divides the Earth into two equal parts in eastern and western hemisphere is called as axis.

 

Ø The plane formed by the orbit of the Earth is known as the orbital plane.

 

 

Ø Axis makes an angle of 66½° with its orbital plane.

 

Ø The circle that divides the day from night on the globe is called the circle of illumination. It does not coincide with the axis.

 

v ROTATION

 

Ø The movement of the Earth around its axis is known as rotation.

 

Ø It completes one rotation in 24 hours which is known as earth day. It is also called as daily motions of the Earth.

 

Ø Rotation of the Earth is very important because:-

§  Day and night are caused due to the rotation of the Earth.

 

§  If the earth did not rotate than some areas became extreme cold and some become extreme hot.

§  Life would not have been possible in such extreme conditions

v REVOLUTION

 

 

Ø The movement of the Earth around the Sun in a fixed path or orbit is called revolution.

 

Ø Earth takes 365 days and 6 hours (365¼ days) to revolve around the Sun.

 

Ø Earth is going around the Sun in an elliptical-orbit.

 

Ø Seasons change due to change in the position of the Earth around the Sun.

 

v LEAP YEAR

 

Ø A year in which there are 366 days or February month has 29 days instead of 28 days is known  leap year.

 

Ø As you know that one revolution completed in 365¼ days. So Six hours saved every year and added to make one day (24 hours) over a span of four years. This surplus day is added in the month of February.

 

Ø So Leap year comes after every four year. To know leap year the year to be divided by four. 2020 is leap year.

 

v POSITION OF THE EARTH DURING REVOLUTION

 

Ø During the revolution the Earth is inclined in the same direction. Seasons change due to the change in the position of the earth around the sun. A year is usually divided into summer, winter, spring and autumn seasons

 

Ø Summer solstice

§  The position of the Earth when the Northern Hemisphere has the longest day and the shortest night. It occurs on 21st June.

§  In this time sun rays fall on tropic of cancer.

§  In the Southern Hemisphere, it is winter season at this time. The days are short and the nights are long.

         Ø Winter Solstice

§  The position of the Earth when the Northern Hemisphere, has short days and long nights. It occurs on 22nd December in winter season.

 

§  In this time sun rays fall on tropic of Capricorn.

§  In the same time Southern Hemisphere has long days and shorter nights and has summer season.

 

       Ø EQUINOX

§  On 21st March and September 23rd, direct rays of the sun fall on the equator and the whole earth experiences equal days and equal nights. This is called an equinox.

§  In March northern hemisphere has spring season and southern hemisphere has autumn season.

§  In September northern hemisphere has autumn season and southern hemisphere has spring season.

 

v DAY AND NIGHT ON POLES

 

Ø During the year sun rays fall in between tropic of cancer to tropic of Capricorn.

 

Ø The areas near the poles receive less heat as the rays of the sun are slanting.

 

Ø During the summer solstice the North Pole is inclined towards the sun and experience continuous daylight for about six months, so there is day for six month. While South Pole experience night almost six month.

 

Ø During the winter solstice the position reverses.

 

 v Terms-

Ø The ancient Indian astronomer Aryabhata had stated that ‘the earth is round and rotates on its own axis.