NCERT - Stars and Solar System Chapter Answers

Class 8th Science, Answers to Ch. 17 - 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

(d) A comet

 (c) Constellation

Answer 1: Constellation is a group of stars that form recognisable shapes. A constellation is not a member of the solar system as it has stars and stars except Sun are not the part of a solar system. Stars do not revolve around the Sun.

Question 2: Which of the following is NOT a planet of the sun?

(a) Sirius

(b) Mercury

(c) Saturn

(d) Earth

 (a) Sirius

Answer 2: Sirius is a star (nearest after Sun and the brightest in the night sky) and not a planet of the sun.

Question 3: Phases of the moon occur because

(a) we can see only that part of the moon which 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 3: (a) Phases of the moon occur because we can see only that part of the moon which reflects light towards us.

Moon does not produce its own light. We are able to see the moon because the sunlight falling on it gets reflected towards us on Earth. Thus, we on Earth, see only that part of the moon from which the light of the sun gets reflected towards us.

Question 4: Fill in the blanks:

(a) The planet which is farthest from the sun is _____________.

(b) The planet which appears reddish in colour is _____________.

(c) A group of stars that appear to form a pattern in the sky is known as a __________.

(d) A celestial body that revolves around a planet is known as a ___________

(e) Shooting stars are actually not ________.

(f) Asteroids are found between the orbits of ____________ and ___________.

Answer 4: (a) The planet which is farthest from the sun is Neptune.

(b) The planet which appears reddish in colour is Mars.

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

(d) A celestial body that revolves around a planet is known as a satellite.

(e) Shooting stars are actually not stars.

(Shooting stars are not stars, they are meteors)

(f) Asteroids are found between the orbits of Mars and Jupiter.

(Asteroids occupy a large gap between the orbits of Mars and Jupiter)

Question 5: Mark the following statement as true (T) or false (F).

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

(b) Mercury is the smallest planet of the solar system. ( )

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

(d) INSAT is an artificial satellite. ( )

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

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

Answer 5 (a) False.

Stars are not a member of the solar system. The sun and the celestial bodies revolving around it form the solar system.

(b) True.

Mercury is the smallest planet of the solar system.

(c) False.

Neptune is the farthest planet in the solar system. (Uranus is the second farthest planet in our Solar System).

(d) True.

INSAT is an artificial satellite. (INSAT - Indian National Satellite System).

(e) False.

There are eight planets in the solar system. They are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune (Before 2006, there were nine planets and Pluto was also included but not as of now).

(f) False.

Constellation Orion can be seen during winters around late evenings. It is one of the most magnificent constellations in the sky, visible to the bare (unaided) eyes.

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

A		B
(i)	Inner planets	(a)	Saturn
(ii)	Outer planets	(b)	Pole star
(iii)	Constellation	(c)	Great Bear
(iv)	Satellite of the Earth	(d)	Moon
		(e)	Earth
		(f)	Orion
		(g)	Mars

Answer 6:

A		B
(i)	Inner planets	(g), (e)	Mars, Earth
(ii)	Outer planets	(a)	Saturn
(iii)	Constellation	(c), (f)	Great Bear, Orion
(iv)	Satellite of the Earth	(d)	Moon

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

Answer 7: Venus appears in the western sky after sunset and is called the evening star.

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

Answer 8: The largest planet of the solar system is Jupiter.

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

Answer 9: A constellation is a group of stars that form a recognisable pattern in the sky. The two well known constellations are Ursa Major and Orion.

Question 10: Draw sketches to show the relative position of prominent stars in (a) Ursa Major and (b) Orion

Answer 10: (a)

Ursa Major appears like a shape of a big dipper. There are three bright stars in the handle and four stars in the bowl of the dipper (as shown in the given figure).

(b) Orion appears like a hunter. There are three bright stars appear in the belt, while five bright stars are arranged in the form of a quadrilateral (as shown in the given figure).

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

Answer 11: (i) Asteroids

A collection of a large number of small objects, gases and dust revolving around the sun. They occupy a large gap between the orbits of Mars and Jupiter. However, these are not planets. These celestial objects are known as asteroids. They are made of rocks and metals.

(ii) Meteors

Meteors are small celestial objects that are seen as bright streaks (flashes of light) of light in the sky. They burnt out on entering the Earth’s atmosphere because of the heat produced by friction. This results in bright streaks in the sky. They are not planets.

Additional:

Meteoroid - It is a small piece of rock which moves about in inter-planetary space. It doesn't reach Earth's atmosphere.

Meteor - it is a small piece of rock which enters Earth atmosphere with high speed and gets burnt due to air friction and is not able to reach Earth's surface.

Meteorite - It is a piece of big rock which even after burning in Earth’s atmosphere manages to strike the Earth's surface.

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

Answer 12: In order to locate the Pole star in the sky, first of all Ursa Major or Big Dipper constellation must be located. The bowl of the Big Dipper consists of four bright stars (as shown in the given figure).

Consider two stars at the end of this bowl. Now, draw an imaginary straight line towards the north direction connecting these two stars (as shown in the given figure).

This imaginary line meets a star called the Pole Star with the length of the imaginary line from the bowl being approximately five times the distance between the two stars of the bowl.

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

Answer 13: No, stars do not move in the sky. The Earth rotates from West to East direction on its own axis. Hence, all stars in the sky (except the Pole star) appear to move from East to West. With reference to the Earth, the Pole star does not appear to move in the sky because it is located straight above the axis of rotation of the Earth in the north direction. It appears to remain stationary at a point in the sky.

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 14: The distance of the stars from the Earth and the distance between the stars are very large. It is inconvenient to express these distances in kilometres as it will have large amount of numbers. Thus, these large distances are expressed in light years. One light year is the distance travelled by light in one year. One light year is equal to 9.46 × 1012 km.

A star is located eight light years away from the Earth. This means that the distance between the star and the Earth is equivalent to the distance travelled by light in eight years, i.e., a star is located 8 × (9.46 × 1012) = 7.6 × 1013 km away from the Earth.

Question 15: The radius of Jupiter is 11 times the radius of the Earth. Calculate the ratio of the volumes of Jupiter and the Earth. How many Earths can Jupiter accommodate?

Answer 15: Earth and Jupiter can be considered as two spheres with radii R and R’ respectively. Given that the radius of Jupiter is 11 times the radius of the Earth.

Thus, R’ = 11 R (R’ is the radius of Jupiter while R is the radius of Earth).

Volume of a sphere of radius r is given by the formula

So, Volume of the Earth with radius R

And, volume of Jupiter with radius R’ and R’ = 11R,

  

The ratio of the volumes of Jupiter and Earth

Hence, the above ratio suggests that Jupiter can accommodate 1331 number of Earths within it.

Question 16: Boojho made the following sketch (Fig. 17.29) of the solar system. Is the sketch correct? If not, correct it.

Answer 16: Planets of the solar system in sequence of their distances from the sun are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Therefore, Boojho’s sketch of the solar system is not correct because he has interchanged the positions of Mars and Venus and also the positions of Uranus and Neptune.

Also, he has shown the Asteroid belt in the gap between the orbits of Jupiter and Saturn. This is not correct. The asteroid belt is located between the orbits of Mars and Jupiter.

The correct sketch of the solar system is shown in the given figure.