NCERT Book Class 6 Geography Globe Motions Of The Earth

MOTIONS OF THE EARTH

As you know that the earth has two types of motions, namely rotation and revolution. 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.

The axis of the earth which is an imaginary line, makes an angle of 66½° with its orbital plane. The plane formed by the orbit is known as the orbital plane. The earth receives light from the sun. Due to the spherical shape of the earth, only half of it gets light from the sun at a time (Figure 3.2). The portion facing the sun experiences day while the other half away from the sun experiences night. The circle that divides the day from night on the globe is called the circle of illumination. This circle does not coincide with the axis as you see in the Figure 3.2. The earth takes about 24 hours to complete one rotation around its axis. The period of rotation is known as the earthday. This is the daily motion of the earth.

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.

REVOLUTION

The second motion of the earth around the sun in its orbit is called revolution. It takes 365¼ days (one year) to revolve around the sun. 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 added to make one day (24 hours) over a span of four years. This surplus day is added to the month of February. Thus every fourth year, February is of 29 days instead of 28 days. Such a year with 366 days is called a leap year. Find out when will the next leap year be? From the Figure 3.3, it is clear that the earth is going around the sun in an elliptical orbit. Notice that throughout its orbit, the earth is inclined in the same direction.

A year is usually divided into summer, winter, spring and autumn seasons. Seasons change due to the change in the position of the earth around the sun

EXERCISE

1. Answer the following questions briefly.

(a) What is the angle of inclination of the earth’s axis with its orbital plane?

(b) Define rotation and revolution.

(c) What is a leap year?

(d) Differentiate between the Summer and Winter Solstice.

(e) What is an equinox?

(f) Why does the Southern Hemisphere experience Winter and Summer Solstice in different times than that of the Northern Hemisphere?

(g) Why do the poles experience about six months day and six months night?

2. Tick the correct answers.

(a) The movement of the earth around the sun is known as

(i) Rotation   (ii) Revolution    (iii) Inclination

(b) Direct rays of the sun fall on the equator on

(i) 21 March   (ii) 21 June     (iii) 22 December

(c) Christmas is celebrated in summer in

(i) Japan       (ii) India            (iii) Australia

(d) Cycle of the seasons is caused due to

(i) Rotation    (ii) Revolution    (iii) Gravitation

Please refer to attached file for NCERT Class 6 Geography Globe-Motions Of The Earth