## Friday, 17 June 2011

### Motions of the Earth : Lesson 3 : CBSE NCERT Class VI (6th) Geography (Social Science) TextBook :: The Earth : Our Habitat

Exercises Solutions : Questions And Answers

Question. Answer the following question briefly.
(a) What is the angle of inclination of the earth's axis with its orbital plane?
Answer. The angle of inclination of the earth's axis with its orbital plane is 66 and half degree which means the Earth remains tilted to one side while it revolves around the Sun at an angle of 66 -1/2 degree.

(b) Define rotation and revolution.
Answer. (1)   Rotation:        The movement of the Earth on its own axis is called rotation. The Earth takes 24 hours to complete one rotation. It causes day and night.
(2)   Revolution:    The movement of the Earth around the Sun in a fixed orbit  is called revolution. The earth takes 365 days and 6 hours to complete one revolution.  It causes seasons.

(c) What is a leap year?
Answer.Every fourth year is a leap year and has 366 days instead of usual 365 days. In leap year, the month of February has 29 days instead of 28 days. This happens because, the time taken by the Earth to revolve around the Sun is 365 days and 6 hours. These extra 6 hours are not included  for 3 consecutive yearly rotation of the Earth, instead in fourth year,  18 hours are added to 365 days 6 hrs to make it 366 days leap year.
(d) Differentiate between Summer and Winter solstice.
Answer. Summer solstice: It is the position of the earth when the Northern Hemisphere has the longest day and the  shortest night. It occurs on 21st June. In the Southern Hemisphere, it is winter season at this time. The days are short and the nights are long.

(e) What is an equinox?
Answer.An  equinox is a celestial phenomenon when  neither of the poles of Earth are tilted towards the sun. Due to this, exactly half of  earth sphere receive sun light and half is in shadow. Thus the whole earth experiences equal days and equal nights.  An equinox happens each year twice,  first on  21st March and 2nd on 23rd September.

(f) Why does the southern Hemisphere experiences  Winter and Summer Solstice in different times than that of Northern Hemisphere.
Answer. The seasons in southern Hemisphere and Northern are exactly the opposite.

(g) Why do the poles experience six months day and six months night?
Answer. When the rays of the sun fall directly on the Tropic of cancer (21st June), the areas near the south pole receive less heat. The North Pole is inclined towards the sun and places beyond the Arctic circle experience continuous daylight. At this time, the Southern Hemisphere has the opposite season. The nights are long and areas beyond Antarctic circle get continuous night. The reverse will happen on 22nd December.

(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) 21st March.    (ii) 21st June.    (iii) 22nd 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.