Soalr System & Observing the sky

Our Solar System

D1. Name the hottest planet in our solar system.   Is it closest to the sun?

Ans: Venus is the hottest planet in our solar system. No Venus is not the closest planet to the sun mercury is the closest one.

D2.How much time does the earth take to

              (i) Revolve once around the sun

              (ii)To complete one rotation about its own axis.

Ans;(i) Earth takes  365 days and 6 hours to revolve once around the sun.

(ii)Earth takes 23 hours 56 minutes to complete one rotation about its own axis.

D3.State the nature of the shape of the orbit of planets.

Ans: The shape of the orbit of planets is elliptical.

D4. Write the meaning of the artificial satellites.

Ans: Artificial satellites are man-made objects which can be made to revolve around the earth to perform various tasks.

E1. How is the sun useful to us?

Ans: Sun is useful to us in the following ways:

i)It is the ultimate source of energy.

ii)  It gives us heat and light

iii) Plant prepares food by using sunlight in the process of photosynthesis.

iv) Sun is essential for the growth and maintenance of all forms of life on earth.

v) Solar energy can be used in solar cookers, solar geysers, calculators, satellites and many other things.

E2. Name the terrestrial planets. Why are they called so?

Ans: Mercury, Venus Earth, and Mars are called terrestrial planets. They are called as terrestrial planets because they are made of mainly rocks and metal.

E3. State the conditions necessary for the existence of life on a planet?

Ans: The conditions necessary   for the existence of life on a planet are:

i)                  Presence of atmosphere

ii)                Presence of liquid (water)

iii)              Right size and the right distance from the sun.

E4. Why do we observe phases of the moon?

Ans: We observe the phases of the moon due to the changes in the relative position of the earth and the moon with respect to the sun.

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Observing the night sky

D1.Why do we usually not see the stars during the day?

Ans: We do not see stars during the daytime because the sun is very close to earth than other stars. Sunlight dominates the lights of other stars, so we can not see stars during the daytime.

D2.In which part of the sky are we likely to find Venus when it is visible as an evening star?

Ans: We usually find Venus is very low near the horizon in the sky.

D3. State the causes of the apparent motion of the sun from east to west?

Ans: The apparent movement of the sun from east to west is due to the rotation of the earth on its axis from west to east.

D4.Name the special star in the northern hemisphere. Why has it been useful for travelers?

Ans: Pole star is the special star of the northern hemisphere. It remains along the axis of the earth and does not change its position due to the rotation of the earth. It indicates north direction, so it is very helpful for travelers to determine the direction.

E1.Define the term constellation?

Ans: A constellation is a group star that appears to form some recognizable pattern or shape in the sky.

E2.In what respects is the pole star different from other stars?

Ans: Pole star lies along the axis of the earth. So it does not change its position due to the rotation of the earth, whereas other stars apparently move from east to west due to the rotation of the earth.

E3. Write two points of difference between a planet and a star.

Stars	Planets
i) stars have their own light	i) planets do not  have their own light
ii) Stars appear like a point	ii) Planets appear as tiny disc
III) stars twinkle	iii) Planets do not twinkle
iv) stars do not change their relative position with other	iv) Planets change their relative position.

E4.   Why do stars appear to slightly shift their position in the night sky?

Ans: The stars appear to slightly shift their position in the night sky due to the rotation of the earth on its own axis from west to east. This shifting of stars is apparent.

E5. Why do stars appear as points to us?

Ans: Stars are huge gaseous balls present very far away from earth. Due to their very large distance from us they appear just like point

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