# NCERT Solutions Class 8 Science Chapter 17

## NCERT Solutions for Class 8 Science Chapter 17

Science is the careful observation and experimentation of the structure and behaviour of the physical, social, and natural worlds. It is essential for human progress, global competitiveness, and innovation. Therefore, the world must continue to improve research, whether it’s discovering new cancer and other illnesses’ remedies or discovering and exploring other galaxies. It isn’t always evident how science influences our daily lives, but it does.

NCERT Class 8 Science Chapter 17 Stars and Solar System familiarises students with outer space and the universe. This helps them learn about the planets in the solar system, celestial objects like the moon, stars, etc., constellations like Orion, the sun, asteroids, meteors, other planets, comets and artificial satellites.

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### Key Topics Covered in NCERT Solutions for Class 8 Science Chapter 17

To make it convenient for the students, Extramarks has listed below the key topics that are covered in NCERT Solutions for Class 8 Science Chapter 17:

 Introduction Phases of the Moon Stars Introducing the Solar System

Let us look at Extramarks’ in-depth information on each subtopic in NCERT Solutions for Class 8 Science Chapter 17- Stars and the Solar System.

Introduction

Extramarks NCERT Solutions for Class 8 Science Chapter 17 introduces students to this chapter. Celestial bodies include planets, stars, the moon, and other celestial bodies. Astronomy is a discipline of science concerned with the study of celestial bodies and their phenomena. One of the observations of celestial bodies that humans may make is the change in the form of the moon every day. The full moon day is when the entire disc of the moon is visible, whereas the new moon day is when just a tiny fraction of the moon is visible. The moon’s phases are the various forms of the luminous part of the moon observed over a month.

Phases of the Moon

The moon is a natural satellite of the earth that we witness practically every night. The moon, being a satellite, follows a predictable course around the earth; even when the moon circles around the earth, the gravitational force between the planet and the natural satellite keeps it in its orbit.

NCERT Solutions for Class 8 Science Chapter 17 explains that the moon’s surface is covered with loose dirt and rocks, which we refer to as lunar soil. In addition, it has craters of various sizes due to meteorites that have struck its surface. These meteorites burn up in our atmosphere before reaching the ground on earth. Therefore, there is no life on the moon since there is no air.

Moon’s different phases

The moon’s phases are the changing forms of the visible part of the moon as seen from earth. The cycle lasts around 29 days, from full moon to new moon and back to full moon.

Understanding the phases of the Moon

NCERT Solutions for Class 8 Science Chapter 17 elaborates that the moon does not create its light but instead reflects it. As a result, distinct areas of the moon’s surface are lit as it rotates around the earth, giving us a different form daily.

The dark side of the Moon

• The moon’s dark side refers to the part of the moon that faces away from the earth.
• The moon’s spin on its axis and revolution around the earth takes about the same amount of time. (≈ 27.3 days). As a result, a viewer always sees the moon’s same face from earth.

The surface of the Moon

The moon’s surface is dry, dusty, and devoid of water. As a result, it features a lot of giant craters and tall mountains.

The gravity on the moon is six times lower than on earth. There is no atmosphere since it is so faint. That is why humans can’t hear on the moon’s surface.

In the above section, NCERT Solutions for Class 8 Science Chapter 17 briefly explains Moon and all the information revolving around it. Refer to Extramarks to receive all the exclusive content and excellent study material.

Stars

NCERT Solutions for Class 8 Science Chapter 17 discusses the Stars and their groups in-depth in the following section. Stars are celestial objects that can generate light. They’re both quite hot and massive. They are primarily hydrogen gas with a little amount of helium. The sun is also a star, and its energy and light are vital to the survival of all kinds of life on earth.

The nuclear fusion events that take place inside stars create light. Hydrogen is transformed into helium, and energy is produced as a by-product. This energy manifests as the light for humans. The sun seems enormous and brilliant in the sky when it is close to us. All other stars, on the other hand, are exceedingly far away from us. Although stars are constantly visible in the sky, they are only visible at night due to the lack of sunshine. Because they are millions of kilometres away from us, they look like points.

Except for the Polestar, the position of the stars changes as seen from the earth’s surface.

Pole Star

• The Pole Star (or Polaris) is a star with a stable location. The Pole Star appears to move around the other stars.
• The constellation Ursa Major can be used to locate it.

Light Year

Light Year is an essential topic in NCERT Solutions for Class 8 Science Chapter 17 that students should pay attention to. A light-year is a unit of measurement for distance. In a Julian year, it is the distance a light photon travels in the vacuum. The value of one light-year, denoted by ly, is constant.

The speed of light is approximately 300,000 kilometres per second. It can traverse around 10 trillion kilometres in a year. A light-year is 9,500,000,000,000 kilometres in length. The kilometre measurement is too tiny to be useful throughout the cosmos.

The earth is eight light minutes from the sun.

Constellation

Another major topic that NCERT Solutions for Class 8 Science Chapter 17 focuses upon is Constellations.

Millions upon thousands of stars may be seen dotting the night sky on a clear moonless night. Some of the patterns, which are made up of groupings of brilliant stars, are easily identifiable, and we refer to them as constellations.

Many of these familiar constellations were named for items or creatures they resembled. The constellations Perseus, Andromeda, Cetus, Cassiopeia, and Pegasus, for example, are all associated with Greek mythology. Pisces, the fish in Greek, is also known in Sanskrit as Meena (fish).

It is because the earth rotates from west to east. Therefore, all of the constellations appear to move from west to east in the sky. Furthermore, in the Southern Hemisphere, all constellations are not visible in the Northern Hemisphere, and vice versa. This is because the world is round, and some constellations are not visible. Almost all of the constellations are visible from the equator.

Introducing the Solar System

What are Celestial objects?

A celestial body is a naturally existing physical entity in the universe outside the earth’s atmosphere, such as the sun, moon, etc.

The Solar System

The Solar System is one of the essential topics of NCERT Solutions for Class 8 Science Chapter 17. A solar system comprises the sun, all planets and celestial bodies that rotate around it. There are eight planets in earth’s solar system and an asteroid belt. Pluto is regarded as a dwarf planet.

All planets in the solar system have fixed orbits around the sun. Planets that are closer to the sun rotate faster than planets that are farther away.

The solar system is enormous, and it’s held together by the sun’s massive gravitational force, which maintains planets and asteroids in orbit around it.

The Earth’s solar system is made up of the Sun, planets, satellites, and other members, all of which play a significant part in the current state of the cosmos. Let’s have a look at the members of the solar system.

Sun

• The sun is the closest star to our planet. Therefore, it constantly produces heat and light.
• For all planets in our solar system, it is the primary heat and light energy source.

The Planets

• Planets are celestial objects that do not produce their heat or light.
• They circle a star in defined trajectories termed orbits, and the period of revolution is the time it takes to travel around the sun once.
• A planet also rotates on its axis, referred to as a rotation.

Our very own Solar System

NCERT Solutions for Class 8 Science Chapter 17 briefly describes each planet and other celestial objects which are a part of our Solar system:

Mercury

• Mercury is the smallest planet in our solar system and the planet closest to the sun.
• Due to the brightness of the sun, it is generally covered. However, it may be seen shortly before sunrise or after sunset.

Venus

• During the night, Venus is the brightest planet.
• It is the hottest planet.
• It is the planet that is nearest to earth.
• It is known as the morning star or evening star because it appears in the eastern sky before daybreak and in the western sky after sunset, despite not being a star.

Earth

• Our solar system’s single livable planet is the earth. The presence of atmosphere and water and the proper distance from the sun is necessary for life to exist.
• The Moon is the sole natural satellite of the earth.
• Seasonal variations are caused by the tilt of the earth’s axis of rotation.

Mars

• Mars is the planet closest to the sun. It is known as the “Red Planet” because of the reddish iron oxide covering its surface, giving it a reddish hue.
• Two natural satellites orbit Mars.

Jupiter

• Jupiter is our solar system’s giant planet. It’s so large that it can hold 1300 piles of the earth despite being just 318 times heavier than the earth.
• At least 67 moons orbit Jupiter.
• Jupiter contains a large red spot, representing a massive storm that has been spinning for years and is twice the size of the earth.

Saturn

• Saturn is our solar system’s second biggest planet. It stands out since it has thousands of lovely rings.
• There are several moons around Saturn.

Uranus

• Uranus moves from west to east on its axis. However, its axis has a significant tilt, giving the impression that it is spinning on its side.

Neptune

• Neptune is our solar system’s eighth and farthest planet. It possesses mighty winds, more potent than any other planet in the solar system.

Comets

• Comets are celestial bodies that travel in lengthy elliptical orbits around the sun. They are generally composed of ice, dust, and gases and have a long tail that points away from the sun.
• As a comet approaches the sun, it warms up, spewing gas jets and forming a massive, luminous head.

Meteors and Meteoroids

• Meteors are tiny objects that reach the earth’s atmosphere at incredible speeds and are mostly remaining fractured asteroids.
• The meteor burns and evaporates before it hits the ground due to friction between the atmosphere and the meteor. That’s why they appear in the sky as dazzling streaks of light.
• When a meteor is big enough to not dissolve in the atmosphere, it can hit the ground. And then it is known as a meteorite.

Artificial Satellites

• Artificial satellites are artificial objects launched from the earth that orbit the planet considerably closer to natural satellites.
• They’re utilised for various things, including remote sensing, weather forecasting, and signal transmission.
• INSAT, IRS, and Sputnik-1 are among the examples of artificial satellites.

### NCERT Solutions for Class 8 Science Chapter 17 Exercise and Solutions

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Class 8 Civics Chapter 17: Very Short Answer Type Questions

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By getting access to NCERT Solutions for Class 8 Chapter 17, students can easily understand all the Star and the Solar System concepts via elaborated answers to various NCERT questions in this chapter

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Q.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

Ans-

The correct option is (c).

Explanation: A constellation is the group of stars which forms recognisable shapes. Hence, it is not a member of the solar system.

Q.2 Which of the following is NOT a planet of the sun?

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

Ans-

The correct option is (a).

Explanation: Sirius is a star and not a planet of the Sun.

Q.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.

Ans-

The correct option is (a).

Explanation: Phases of the moon are seen because we can see only that part of the moon which reflects light towards us.

Q.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 __________.
(e) Shooting stars are actually not ____________.
(f) Asteroids are found between the orbits of _________ and _________ .

Ans-

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

Q.5 Mark the following statements 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. ( )

Ans-

(a) Pole star is a member of the solar system. (False)
Explanation: Stars are not the member of the solar system. Only Sun and the celestial bodies which are revolving around the Sun are the parts of the solar system.

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

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

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

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

(f) Constellation Orion can be seen only with a telescope. (False)
Explanation: Orion can be seen during winters around late evenings. It is one of the most magnificent constellations in the sky and can be seen by naked eyes.

Q.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

Ans-

 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

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

Ans-

Venus (evening star) can be seen in the western sky after sunset.

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

Ans-

Jupiter is the largest planet of the solar system.

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

Ans-

A constellation is a group of stars that forms a recognisable pattern in the sky. The two very important constellations are Ursa Major and Orion.

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

(a) Ursa Major and (b) Orion

Ans-

(a) Ursa Major: It looks like a big dipper. There are three bright stars in the handle and four stars in the bowl of the dipper.

(b) Orion: It looks like a hunter. Three bright stars appear in the belt, while five bright stars are arranged in the form of a quadrilateral.

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

Ans-

1. Asteroids: These are the collection of a large number of small objects, gases and dust revolving around the Sun. They cover a large gap between the orbits of Mars and Jupiter.
2. Meteors: They are small celestial objects that are seen as bright streaks 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.

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

Ans-

The Pole star can be located with the help of Big Dipper constellation. In Big Dipper constellation, the bowl has four bright stars. Now, trace an imaginary straight line towards the Northern direction connecting two stars at the end of this bowl. This imaginary dotted line joins to a star known as the Pole Star.

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

Ans-

The stars do not move in the sky. However, the stars seem to move in the sky for an observer on the Earth. It is because the Earth rotates from west to east on its axis. Hence, all the stars in the sky appear to move from east to west except Pole star as it is located above the axis of rotation of the Earth in the north direction.

Q.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?

Ans-

The distance between stars or distance of a star from the Earth is so large that it is inconvenient to express these distances in kilometers. Therefore, these large distances are measured in light years. One light year is equal to the distance travelled by light in one year and is equal to 9.46 × 1012 km. If a star is located eight light years away from the Earth, it means distance between the star and the Earth is = 8 × (9.46 × 1012) km or 7.6 × 1013 km away from the Earth.

Q.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 accomodate?

Ans-

$\begin{array}{l}\text{Earth and Jupiter can be assumed as two spheres}\text{.}\\ {\text{Let, radius of the Earth = r}}_{\text{1}}\\ {\text{radius of the Jupiter = r}}_{\text{2}}\\ \text{As radius of Jupiter is 11 times the radius of Earth,}\\ {\text{Hence, r}}_{\text{2}}={\text{11 r}}_{\text{1}}\\ \text{Volume (V) of a sphere of radius r is given as,}\\ \text{V =}\frac{4}{3}\pi {r}^{3}\\ \therefore {\text{Volume of Earth, V}}_{\text{1}}=\frac{4}{3}\pi {r}_{1}{}^{3}\text{}\dots \text{(i)}\\ {\text{Volume of Jupiter, V}}_{\text{2}}\text{=}\frac{4}{3}\pi {r}_{2}{}^{3}\text{=}\frac{4}{3}\pi {\left(11\text{\hspace{0.17em}}{r}_{1}\right)}^{3}\text{}\dots \text{(ii)}\\ \text{On dividing equation (ii) by (i),}\\ \text{}\frac{{\text{V}}_{\text{2}}}{{\text{V}}_{\text{1}}}=\frac{1331\left(\frac{4}{3}\pi {r}_{1}{}^{3}\right)\text{}}{\frac{4}{3}\pi {r}_{1}{}^{3}\text{}}=1331\\ {\text{or, V}}_{\text{2}}={\text{1331 V}}_{\text{1}}\\ \text{Hence, Jupiter can accommodate 1331 Earths}\text{.}\end{array}$

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

Ans-

The sequence of the planets in the solar system from the Sun is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Hence, the sequence of the planets of solar system is not correctly sketched by Boojho. Moreover, the asteroid belt should be located between the orbits of Mars and Jupiter. The correct sketch of the solar system is shown in the figure given below.