## CBSE NCERT Solved Question Answer

Q1. Name the two motions of the earth.
Revolution and Rotation

Q2. What is Rotation?
Rotation is the movement of the earth on its axis.

Q3. What is Revolution?
The movement of the earth around the sun in a fixed path or orbit is called Revolution.

Q4. What is Orbital Plane?
The plane formed by the orbit is known as the orbital plane.

QS. What is the angle of inclination of the earth's axis with its orbital plane?
The axis of the earth, which is an imaginary line, makes an angle of 662° with its orbital plane.

Q6. Why only one half of the Earth gets light at one time?
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. The portion facing the sun experiences a day, while the other half away from the sun experiences night.

Q7. What is Circle of Illumination?
The circle that divides the day from night on the globe is called the Circle of illumination.

Q8. What time does the Earth take to complete one Revolution?
It takes 36S11 days (one year) to revolve around the sun.

Q9. Name the different seasons on the Earth.
A year on the Earth is usually divided into summer, winter, spring and autumn seasons.

Q10. Why do the seasons change?
Seasons change due to the change in the position of the earth around the sun.

Q11. What is an Equinox?
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.

Q12. What time does the Earth take to complete one Rotation? What is it also called?
The earth takes about 24 hours to complete one rotation around its axis. The period of rotation is known as the Earth day.

Q13. What will 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.

Q14. Why do poles experience about six months of day and six months of night?
When Northern Hemisphere is tilted towards the sun, the North Pole is also inclined towards it and the places beyond the Arctic Circle experience continuous daylight for about six months and the South Pole experiences night at this time.

Q15. What is a Leap Year?
(i)   Earth takes 36S11 days (one year) to revolve around the sun. We consider a year as consisting of 36S days only and ignore six hours for the sake of convenience.
(ii) 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. Such a year with 366 days is called a leap year.

Q16. What is Summer Solstice?
(iii)                      On 21st June, the Northern Hemisphere is tilted towards the sun. The rays of the sun fall directly on the Tropic of Cancer and the North Pole is also inclined towards the sun.
(iv)                      Since a large portion of the Northern Hemisphere is getting light from the sun, it is summer in the regions north of the equator.
(v) The longest day and the shortest night at these places occur on 21st June. This position of the earth is called the Summer Solstice.

Q17. What is Winter Solstice?
(vi)                      On 22nd December, the Tropic of Capricorn receives direct rays of the sun as the South Pole tilts towards it.
(vii)                    As the sun's ray's fall vertically at the Tropic of Capricorn, a larger portion of the Southern Hemisphere gets light.
(viii)                   Therefore, it is summer in the Southern Hemisphere, with longer days and shorter nights. This position of the earth is called the Winter Solstice.