4.2   Text Questions :

1.  What is the angle of inclination of the earth’s axis with its orbital plane?
Ans: The earth’s axis forms an angle of 66½0 with the orbital plane.

2.  Define rotation and revolution.
Ans:
-Rotation is the movement of the earth around its own axis. It takes the earth 24 hours to complete a rotation.
-Revolution is the movement of the earth around the sun in a fixed orbit. It takes 365 days and 6 hours to complete a revolution.

3.  What is a leap year?
Ans:
A leap year is a year that has 366 days instead of the usual 365 days as the earth takes 365 days and 6 hours to complete a rotation. The extra 6 hours is the added to each year and after 4 years it becomes 1 full day. Then it is added to the fourth year in February. So we have 29 days in February instead of 28 days in a leap year.

4.  Differentiate between the summer and winter solstice.
Ans:
Summer solstice                                Winter solstice

a.  The sun falls directly on the              a) The sun falls directly on the
tropic of Cancer so northern                   Tropic of  Capricorn so the
hemisphere has heat and light.               Southern hemisphere gets .
heat and light .

b.  The north pole is tilted towards      b) South pole is tilted towards
the sun.                                                       the sun.

c.  So it is summer in the northern       c) It is summer in the southern
hemisphere.                                               hemisphere.

d.  It occurs on 21st June in                    d) It occurs on 22nd December
northern hemisphere.                              in the southern hemisphere.

5.  What is an Equinox?
Ans:
An Equinox is when neither of the poles is tilted towards the sun. The sun rays falls directly on the equator. This causes the days and nights to be equal. It occurs twice in a year on 21st March and 23rd September.

6.  Why does the southern hemisphere experience winter and summer solstice in different times than that of the northern hemisphere?
Ans:
On 21st June the northern hemisphere is tilted towards the sun so it will have summer solstice while the southern hemisphere will have winter solstice. On 23rd December the southern hemisphere is tilted towards the sun so southern hemisphere will have summer solstice and northern hemisphere will have winter solstice.

7.  Why do poles experience about six months days and six months night?
Ans: The poles experience about six months days and six months night because when the northern hemisphere tilts towards the sun, the north pole gets light for the whole day. But when the north pole is in the  light the south pole does not get light. This takes place for a period of six months.

1. The movement of the earth around the sun is known as ___________ .
a. Rotation                 b. Revolution √                    c. Inclination

2. Direct rays of the sun fall on the equator on__________ .
a. 21st March √             b. 21st June                         c. 22nd December

3. Christmas is celebrated in summer in___________ .
a. Japan                     b. India                                c. Australia √

4. Cycle of the seasons is caused due to ___________ .
a. Rotation                b. Revolution √                     c. Gravitation