## Chapter 3 - Motions of the Earth

Question 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?

a) The angle of inclination of the earth’s axis with its orbital plane is 66½°.

b) 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.

c) 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.

d)
Summer Solstice - When the Southern hemisphere experiences the winter season and it is summer in the northern hemisphere. At that point in time, the position of the earth on 21st June is called the Summer Solstice.
Winter Solstice - When the Southern hemisphere experiences the summer season and the reverse occurs at the Northern hemisphere. At that point in time, the position of the earth on 22nd December is called the Winter Solstice.

e) On 21st March and September 23rd, direct rays of the sun fall on the equator. At this position, neither of the poles is tilted towards the sun; so, the whole earth experiences equal days and equal nights. This is called an equinox.

f) The Earth is always revolving and it is divided into two hemispheres. The part of the earth which faces the sun experiences summer and the part away from the sun experiences winter. Therefore, Southern Hemisphere experience Winter and Summer Solstice at different times than that of the Northern Hemisphere.

g) The Poles experience 6 months of day and six months of nights due to the inclination of the earth on its own axis. This inclination keeps one pole towards the sun and another pole away from the sun for 6 months each. This is the reason behind this condition.

Question 2: Tick the correct answers.
a) The movement of the earth around the sun is known as
i) Rotation
ii) Revolution
iii) Inclination
ii) Revolution

b) Direct rays of the sun fall on the equator on
i) 21 March
ii) 21 June
iii) 22 December
i) 21 March

c) Christmas is celebrated in summer in
i) Japan
ii) India
iii) Australia
iii) Australia

d) Cycle of the seasons is caused due to
i) Rotation
ii) Revolution
iii) Gravitation
ii) Revolution

Question 3: Fill in the blanks.
a) A leap year has _______________ number of days.
b) The daily motion of the earth is _______________.
c) The earth travels around the sun in ______________ orbit.
d) The sun’s rays fall vertically on the Tropic of ___________ on 21st June.
e) Days are shorter during ___________ season.