Class VI

CHAPTER-4 THE MOTIONS OF THE EARTH (DAY NIGHT AND SEASONS)

D. Answer the following questions in brief:

Q1. What is rotation? How much time does Earth take in completing one rotation?

Ans1- i) The earth is continuously spinning on its imaginary axis from west to east and completes one round in about 24 hours.

ii) The motion of the earth is called rotation.

iii) It causes day and night.

Q2. What is meant by the revolution of the Earth?

Ans2- i) The movement of earth around the sun in an elliptical orbit in one year is called revolution.

ii) It revolves around the Sun in 365⅟4 days.

iii) It causes change in seasons.

Q3. What is a leap year?

Ans3- The year in which February is of 29 days instead of 28 days and we have the year of 366 days is called a leap year.

Q4. What is an equinox? Which seasons are indicated by it in both the hemispheres?

Ans4-

1) The situation when the sun rays are vertical over the equator is called an equinox.

2) The duration of day and night becomes equal in both the hemispheres i.e. 12 hours day and 12 hours night

3) Both the hemispheres receive equal amount of heat.

   It causes spring and autumn seasons in both the hemispheres

Q5- Why does the duration of day and night change in a year.

Ans5- The duration of the day and night changes in a year because:

i) The earth is tilted on its axis. As it orbits the Sun, a different part of the earth faces the Sun.

ii) When the Hemispheres face the Sun, the length of the day is more than night.

iii)  When the hemispheres are far away from the Sun, it is just the opposite. The nights are longer than days.

E. Answer the following questions:

Q1. Why days and nights are equal on 21^st march at all places on the earth? Explain

Ans1- Days and nights are equal on 21^st march at all places on the Earth because:

i) The sunrays are vertical over the equator.

ii) The duration of day and night becomes equal in both the hemispheres, i.e. 12 hours day and 12 hours night.

iii) Both the hemispheres receive equal amount of heat.

Q2. Explain with the help of a diagram, why seasons are reversed between northern and southern hemisphere?

Ans2- i) Position of Earth on 21^st June –

a) Northern Hemisphere is inclined towards the sun thus experiences summer season which is called as summer solstice

b) Southern Hemisphere is away from the sun thus experiences winter season which is called as winter solstice

ii) Position of Earth on 23^rd September –

 Both the hemispheres receive same amount of heat and hence

a) Northern hemisphere – Autumnal equinox

b) Southern Hemisphere – Vernal Equiniox

iii) Position of Earth on 22^nd December-

a) Southern Hemisphere is inclined towards the sun thus experiences summer season which is called as summer solstice

b) Northern Hemisphere is away from the sun thus experiences winter season which is called as winter solstice

iv) Position of Earth on 21^st March

 Both the hemispheres receive same amount of heat and hence

a) Northern hemisphere – Vernal Equinox

b) Southern Hemisphere –Autumnal Equinox

(DIAGRAM ON PAGE NO. 32)

Q3. Why does the month of February have 29 days, after every 4 years?

Ans3- The month of February has 29 days, after every 4 years because:

i) The earth completes one revolution in 365 days and about 6 hours.

ii) We consider 365 days in a year.

iii) The remaining 6 hours are added over a period of 4 years till they become 24 hours or one day.

iv) This extra day is added to the month of February every four years to make it a month of 29 days instead of 28 days.

v) The year of 366 days is called leap year.

Q4. How do day and night occur on the earth? Explain with the help of a diagram?

Ans4- i) The earth completes one rotation in about 24 hours.

ii) So, the earth faces the sun while rotating from west to east.

iii) Each part of the earth facing the sun, is illuminated by sunlight turn by turn.

iv) The lighted half part of the earth that faces the sun has day.

v) While the other part of the earth that is not facing the sun, experiences night.

(DIAGRAM ON PAGE NO.30)