LESSON 3 Geography
LESSON 3 Geography
LESSON 3 Geography
1. b 2. a 3. c 4. a 5. c 6. b
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5. It is spring in the Northern Hemisphere and autumn in the Southern Hemisphere
On
a. 23rd September b. 21st March c. 22 nd December d. 21 st June
1. a 2. d 3. a 4. c 5. b
1. b 2. a 3. b 4. b 5. c
6. c 7. d 8. a 9. a 10. a
11. b 12. c 13. a 14. b
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III. Fill in the blanks
1. d 2. c 3. b 4. a
1. e 2. d 3. b 4. c 5. a
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I. True or False
1. When nights are longer than days in Southern hemisphere this position of earth
is called as winter solstice.
2. The sun goes around the earth in an elliptical orbit.
3. During summer solstice the season in the north hemisphere is winter.
4. On 21st March and 23rd September the whole earth experiences equal days and
nights.
5. Rotation is movement of earth on its axis.
1. The axis of the earth makes an angle of 231 2 with its orbital plane.
2. Every five year, February is of 29 days instead of 28 days.
3. Season changes due to the change in the position of the earth around the sun.
4. When there is summer in the Northern Hemisphere, it is spring in the Southern
Hemisphere.
5. Life is not possible in extreme conditions.
1. What is the angle of inclination of the earth’s axis with its orbital plane?
The angle of inclination of the earth’s axis is 661 2 with its orbital plane.
2. Define leap year?
Rotation is the movement of earth on its axis. Revolution is the movement of
the earth around the sun on a fixed orbit.
3. What is a leap year?
The earth rotates around the sun for 365 days and 6 hours. For our
convenience, we count only 365 days. So after every 4 years, when 24 hours get
completed we add the time as additional day in February which is of 29 days.
Thus every fourth year is known as leap year.
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4. What is an equinox?
On 21st March and 23rd September, direct rays of sun fall on the equator.
During this position, neither of the poles is tilted towards the sun due to which
the whole earth experiences equal days and equal nights. This is known as an
equinox.
5. What is circle of illumination?
The circle that divides the day from night on the globe is called the circle of
illumination.
6. What is axis?
The imaginary line which passes from the centre of the earth and joins the two
poles namely North Pole and South Pole is known as axis.
2. Why do the poles experience about six months day and six months night?
(i) During summer solstice, North Pole is inclined towards the sun and the places
beyond the Arctic Circle face continuous daylight for six months.
(ii)During the same time, the South Pole moves away from the sun and places
above the Arctic Circle face continuous daylight for six months.
(iii) During winter solstice, the situation is reversed. South Pole comes in light
while North Pole goes in dark.
(i) It is because of the rotation that days and nights take place.
(ii) Half of the earth receiving sunlight experiences day and the other half night.
(iii) This alternate day and night phenomenon keeps going on over time. These
days and night are not equal in all parts of the world.
(iv) It is attributed to the inclination of the earth that day and night is of equal
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length at the equator and unequal as we move towards the pole.
(v) Again, here we can refer to the fact that the earth is inclined to the plane of
its orbit (661 2 °) which makes one of the hemispheres to lean against the sun
for a greater period, let’s say six months.
(i) The portion of the earth facing the sun would always experience day, thus
bringing continuous warmth to the region.
(ii) The other half world remain in darkness and be freezing cold all the time.
(iii) Life would not have been possible in such extreme conditions.
1. Why does the Southern Hemisphere experience winter and Summer Solstice
in different times than that of the Northern Hemisphere?
While the earth revolves around the sun, one hemisphere tilts towards the
sun while the other moves away from the sun. Thus on 22 nd December, Southern
Hemisphere tilts towards the sun and the Northern Hemisphere moves away from
it. The situation is reversed on 21st June. The hemisphere tilted towards the
sun gets heated up as compared to the hemisphere away from the sun. It is due
to this that Southern Hemisphere experiences winter and summer solstice at
different time as that of Northern Hemisphere.
2. How is the earth’s axis inclined? What is its effect?
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The direction of rotation is west to the east. The sun, moon and stars rise from
the east and set in the west.
At any given point of time half of the earth faces the sun while half remains in
dark or away from the sun. That illuminated part is called “Circle of Illumination”
3. How does elliptical orbit of the earth affect it?
(i) On 21st June, the northern hemisphere is tilted towards the sun.
(ii) The rays of the sun fall directly on the Tropic of Cancer. As a result, we
receive heat. So they experience summer.
(iii) At the same time in the Southern Hemisphere, all these conditions are
reversed. It is winter season there.
(iv) The nights are longer than the days here.
(v) So, 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.
4. How does the earth’s one revolution affect months and seasons?
(i) The Earth takes about 365 days and 6 hours to complete one revolution.
(ii) In order to avoid the confusion and problem arising out of the fraction it was
decided that a day would be added to the calendar every year in the month of
February and for this every fourth year is called “ Leap year”.
(iii) This time taken by the earth for completing a revolution, actually determines
the length of the seasons, let’s say summer, autumn, winter and spring seasons.
5. Examine the concept of summer solstice.
The line which separates the darkened portion and the illuminated one is
called “Circle of Illumination”.
On June 21, the northern half of the earth is inclined towards the sun and
southern half is away from it. The sun rays fall vertically on the Tropic of
Cancer (231 2 ° ) due to which the Northern Hemisphere becomes extremely
hot and warm. There is high temperature condition in the Northern Hemisphere
and it is due to the two facts. Firstly, inclination of earth’s axis and secondly
direct angle of sun rays at the Tropic of Cancer.
It is summer season and the days are longer and nights are shorter in the north
of the equator. Whereas in the south, the sun rays can reach up to only
Antarctica circle (661 2 ° ), after that there is complete darkness for six
months.
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6. Examine the concept of winter solstice.
On December 22, (slight variation in date from year to year) due to
inclination southern half of the earth faces the sun. This is the situation just
opposite to that of the summer solstice. More are of the Southern Hemisphere
is facing the sun hence it is summer season and less area of the northern
hemisphere is exposed to the sun so it is winter season. These sun rays are
vertical at Tropic of Capricorn (661 2 ° ), due to which maximum heating takes
place over that region (661 2 ° ) only after that its complete darkness or night
for six months. Now the days are longer and nights are shorter in this
hemisphere and vice versa for Northern Hemisphere where sun’s rays can reach
up to Arctic Circle only.
7. How are day and nights caused by the rotation of the earth?
Days and nights are caused by the rotation of the earth on its axis which
is tilted at about 661 2 ° to the plane of the ecliptic or orbit. Due to this
inclination the whole world experiences the unequal length of days and nights.
From March 21 to June 21 the days are longer in the northern hemisphere and
vice-versa in the south of the Equator.
From June 21 to September 23, the phenomena starts reversing, that is, day
starts becoming shorter in Northern Hemisphere and longer in the Southern
Hemisphere. On September 23, day and night become equal and after this date
till 22nd December, the day length in northern hemisphere goes on decreasing and
in southern hemisphere, it goes on increasing. In this way again the pattern is
reversed. After December 22, the day length starts increasing with the
approaching of spring equinox.
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