Class 8 Science NCERT Solutions for Chapter – 17 Stars and the Solar System

Stars and the Solar System

Question 1.
Which of the following is NOT a member of the solar system?

(a) An asteroid
(b) A satellite
(c) A constellation
(c) A comet

Answer:
(c) A constellation

Question 2.
Which of the following is NOT a planet of the Sun?

(a) Sirius
(b) Mercury
(c) Saturn
(d) Earth

Answer:
(a) Sirius

Question 3.
Phases of the moon occur because

(a) We can see only that part of the moon that reflects light towards us.
(b) Our distance from the moon keeps changing.
(c) The shadow of the Earth covers only a part of the moon’s surface.
(d) The thickness of the moon’s atmosphere is not constant.

Answer:
(a) We can see only that part of the moon that reflects light towards us.

Question 4.
Fill in the blanks :

(a) The planet which is farthest from the Sun is ______.
Answer:
Neptune

(b) The planet which appears reddish in color is ______.
Answer:
Mars

(c) A group of stars that appear to form a pattern in the sky is known as a ______
Answer:
constellation

(d) A celestial body that revolves around a planet is known as ______
Answer:
Satellite

(e) Shooting stars are actually not ______
Answer:
Stars

(f) Asteroids are found between the orbits of ______ and ______
Answer:
Mars
Jupiter

Question 5.
Mark the following statements is true (T) or false (F) :

(a) Pole star is a member of the solar system.
Answer:
False

(b) Mercury is the smallest planet in the solar system.
Answer:
True

(c) Uranus is the farthest planet in the solar system.
Answer:
False

(d) INSAT is an artificial satellite.
Answer:
True

(e) There are nine planets in the solar system.
Answer:
False

(f) Constellation Orion can be seen only with a telescope.
Answer:
False

Question 6.
Match items in column A with one or more items in column B :

Column AColumn B
Inner planets1. Saturn
Outer planets2. Pole star
Constellation3. Great Bear
Satellite of the Earth4. Moon
5. Earth
6. Moon
7. Mars

Answer:

Column AColumn B
Inner planetsEarth, Mars
Outer planetsSaturn
ConstellationGreat Bear, Orion
Satellite of the EarthMoon

Question 7.
In which part of the sky can you find Venus if it is visible as an evening star?

Answer:
Venus appears in the western sky just after sunset.

Question 8.
Name the largest planet of the solar system.

Answer:
Jupiter is the largest planet in the solar system.

Question 9.
What is a constellation? Name any two constellations.

Answer:
A group of stars that has a recognizable shape is called a constellation. Ursa Major and Orion are two examples of constellations.

Question 10.
Draw sketches to show the relative positions of prominent stars

Answer:
(1) Ursa Major
NCERT Solutions for Class 8 Science img 46
(2) Orion

NCERT Solutions for Class 8 Science img 47

Question 11.
Name two objects other than planets that are members of the solar system.

Answer:
Satellites and asteroids are the objects that too, are members of the Solar system.

Question 12.
Explain how you can locate the Pole star with the help of Ursa Major.

Answer:
To locate the Pole Star we should look towards the northern part of the sky and identify Ursa Major. We may look at the two stars at the end of Ursa Major. A straight line passing through these stars is imagined and is extended towards the north direction. This line will lead to a star that is not too bright. This is the Pole star.

Question 13.
Do all the stars in the sky move? Explain.

Answer:
No, no star moves in the sky. They appear to move from east to west because the Earth rotates from west to east about its axis.

Question 14.
Why is the distance between? stars expressed in light years? What do you understand by the statement that a star is eight light-years away from the Earth?

Answer:
The distance between stars is so large that it cannot be expressed in terms of a kilometer. That is why very large distances, are expressed in another unit known as light year. One light-year is the distance traveled by light in one year. If the distance of a star is eight light-years, it means that this distance is the distance traveled by light in eight years.

Question 15.
The radius of Jupiter is ll. times the radius of the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. How many Earths can Jupiter accommodate?

Answer:
If the radius of the Earth is r. Then, the radius of Jupiter is Hr. So, the ratio of the volumes of Jupiter and the Earth is
NCERT Solutions for Class 8 Science img 45
So,.1331 Earths can accommodate within Jupiter.

Question 16.
Boohoo made the following sketch (Fig. 17.29′, Textbook page 236) of the solar system. Is the sketch correct? If not, correct it.

Answer:
No, the sketch is not correct. The positions of Mars and Venus should be inter-changed. Similarly, the positions of Neptune and Uranus should also be interchanged. And asteroids should be in between the orbits of Mars and Jupiter.

InText Questions and Answers

Question 1.
Do all of them appear to twinkle? Do you find any star-like object which does not twinkle?

Answer:
All of the celestial bodies in the sky do not appear to twinkle. Yes, I could find some star-like objects which do not twinkle.

17.1 The Moon

Question 2.
Is there a change in the shape of the moon every day?

Answer:
Yes, there is a change in the shape of the moon every day.

Question 3.
Are there days when the shape of the moon appears to be perfectly round?

Answer:
Yes, the moon appears to be perfectly round on the full moon day.

Question 4.
Are there days when the moon cannot be seen at all even if the sky is clear?

Answer:
On the fifteenth day after the full moon day, the moon is not visible even if the sky is clear.

Question 5.
Why does the moon change its shape every day?

Answer:
We see only that part of the moon from which the light of the Sun is reflected towards us. The size of the illuminated part of the moon visible from the Earth increases each day after the new moon day.

After the full moon day, the sunlit part of the moon visible from the Earth decreases in size every day. That is why the moon appears to change its shape every day.

Question 6.
Can you now guess the relative positions of the Sun, moon, and the Earth on the day of the full moon and on the day? of the new moon? Sketch these positions in your notebook.

Answer:
The relative positions of the Sun, moon, and the Earth on the day of the full moon is the moon is in between the Sun and the Earth. All of these three are in the same straight line. On the day of the new moon, the Earth is in between the moon and the Sun. All these three are in the same straight line.
NCERT Solutions for Class 8 Science img 48

Question 7.
In which part of the sky would you look for the full moon?

Answer:
West

Question 8.
I have heard that we never see the backside of the moon from the Earth. Is it true?

Answer:
Yes, it is true

Activity 17.3

Question 1.
Can your friend see you back?

Answer:
No, my friend cannot see my back.

Question 2.
How many rotations did you complete in one revolution?

Answer:
I completed only one rotation in one revolution.

Question 9.
Can any life exist on the moon?

Answer:
No, no life can exist on the moon.

Question 10.
Can we hear any sound on the moon?

Answer:
No, as there is no atmosphere on the moon, we cannot hear any sound there.

Question 11.
We learned in chapter 13 that sound cannot travel when there is no medium. Then how can we hear any sound on the moon?

Answer:
With the help of earphones fitted with radio devices, we can hear sounds on the moon.

17.2 The Stars

Question 12.
What other objects do you see in the night sky?

Answer:
Besides stars, we see various planets, constellations, asteroids, etc. in the sky at night.

Question 13.
Are all the stars equally bright?

Answer:
No. Some are very bright, others are dim.

Question 14.
Are they of the same color?

Answer:
They emit white light, so they look bright. Of course, some look very bright whereas others look dim. ,

Question 15.
Why does it (sun) appear so large compared to the other stars?

Answer:
The stars are a million times far away from the Sun. This means that the Sun is the nearest star to the Earth. That is why the Sun appears so bright.

Question 16.
Can you read this distance in kilometers conveniently?

Answer:
No, it is not possible to read this distance in millions of kilometers. Such distances are expressed in another unit known as light year.

Question 17.
If light from stars takes years to reach us, I wonder if we are looking into the past when we look at stars.

Answer:
Yes, we are looking into the past.

Question 18.
I want to know why we do not see the stars during the day. Why are they visible only at night?

Answer:
In fact, the stars are present in the sky during the daytime also. However, they are not visible then because of the brightness of the sunlight.

Question 19.
What do you find? Do you find any change in the positions of the stars in the sky?

Answer:
Yes, the stars appear to move from east to west. A star that rises in the east in the evening sets in the west in the early morning.

Question 20.
Why do stars appear to move from east to west?

Answer:
The stars appear to move from east to west, as the Earth, from where we see them, rotates from west to east about its axis.

Activity 17.4

Question 1.
In which direction will the objects in the room appear to move?

Answer:
The objects appear to move in the opposite direction.

Question 2.
Do you see them moving in the direction opposite to your motion?

Answer:
Yes

Question 21.
My grandfather told me that there is one star in. the sky which does not move at all. How is it possible?

Answer:
If any star lies on or closes to the Earth’s axis of rotation, it will not appear to move. The star which does not move at all is the “Pole Star”.

Activity 17.5

Question 1.
Is there any star that does not appear to move? Where is this star located?

Answer:
Yes. The star pasted at the central rod of the umbrella does not appear to move.

17.3 Constellations

Question 22.
In the cart you see some stars forming groups with shapes like those in Fig. 17.11 (Textbook, page 222)?

Answer:
Yes. I can see some stars forming groups that have a recognizable shape. These are called constellations.

Activity 17.6

Question 1.
Do you find any change in its shape? Do you find any change in its position?

Answer:
The shape of the constellation does not change. It remains the same. As the constellation appears to move in the sky from east to west, it means that its position changes.

17.4 The Solar System

Question 23.
I have read that there are nine planets in the solar system.

Answer:
No, Pluto is now not a part of our solar system. Now there are only eight planets in our Solar system.

Question 24.
Can you distinguish between planets and stars?

Answer:
Yes. Planets do not have their own light whereas stars have. Also, the planets keep changing their position with respect to the stars.

Question 25.
I wonder, why the planets do not collide while revolving around the Sun.

Answer:
As they have fixed orbits of revolution, they do not collide while revolving around the Sim.

Activity 17.9

Question 1.
Do they collide with one another?

Answer:
No, they will not collide with one another, because they have fixed orbits of their own.

Question 26.
The Earth revolves around the Sun. Does it make Earth a satellite of the Sun?

Answer:
The Earth can be said to be a satellite of the Sun, though generally, we call it a planet of the Sun.

Question 27.
Does it mean that on Venus, the Sun would rise in the west and set in the east?

Answer:
Yes, on Venus the Sun rises in the west and sets in the east because the direction of rotation of Venus is from east to west.

Question 28.
If I am 13 years old, how many times have I gone around the Sun?

Answer:
I would have gone 13 times around the Sun.

Question 29.
Boojho has a naughty idea! “If we imagine Saturn in a large pool of water then it will float (Fig. 17.23 Textbook page 230).

Answer:
Yes, it will float.

17.5 Some Other Members of the Solar System

Question 30.
Can you tell, when will Halley’s comet will be visible again?

Answer:
Halley’s comet will be visible again in the year 2062.

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