Class 8 Science || Chapter 18 - Starts & the Solar System (Exercise Solutions)
NCERT Solutions for Class 8 Science – Chapter 17: Stars and the Solar System
Which of the following is NOT a member of the solar system?
(c) A constellation. A constellation is a group of distant stars forming a pattern, not an object revolving around the Sun.
Which of the following is NOT a planet of the sun?
(a) Sirius. Sirius is a star, whereas the Sun has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Phases of the moon occur because
(a) We see only the sunlit part of the Moon that faces Earth, so its visible shape changes as the Moon goes around Earth.
(a) The planet which is farthest from the sun is _________.
Ans: Neptune.
(b) The planet which appears reddish in colour is _________.
Ans: Mars.
(c) A group of stars that appear to form a pattern in the sky is known as a _________.
Ans: Constellation.
(d) A celestial body that revolves around a planet is known as a _______.
Ans: Satellite.
(e) Shooting stars are actually not _________.
Ans: Stars. They are glowing meteors burning in Earth’s atmosphere.
(f) Asteroids are found between the orbits of ____ and _____.
Ans: Mars and Jupiter.
(a) Pole star is a member of the solar system.
Ans: FalseFalse – It is a distant star, not part of the solar system.
(b) Mercury is the smallest planet in the solar system.
Ans: TrueTrue – It has the smallest size among all planets.
(c) Uranus is the farthest planet in the solar system.
Ans: FalseFalse – Neptune is farther from the Sun than Uranus.
(d) INSAT is an artificial satellite.
Ans: TrueTrue – It is a man‑made satellite.
(e) There are nine planets in the solar system.
Ans: FalseFalse – There are eight planets.
(f) Constellation Orion can be seen only with a telescope.
Ans: FalseFalse – Orion is bright and can be seen with the naked eye.
Match items in column A with one or more items in column B.
Column A
(i) Inner planets
(ii) Outer planets
(iii) Constellation
(iv) Satellite of the Earth
Column B
a) Saturn b) Pole star c) Great Bear d) Moon e) Earth f) Orion g) Mars
(i) Inner planets – e) Earth, g) Mars
(ii) Outer planets – a) Saturn
(iii) Constellation – c) Great Bear, f) Orion
(iv) Satellite of the Earth – d) Moon
In which part of the sky can you find Venus if it is visible as an evening star?
Venus, as an evening star, is seen in the western sky just after sunset.
Name the largest planet of the solar system.
Jupiter is the largest planet in the solar system; Mercury is the smallest.
What is a constellation? Name any two constellations.
A constellation is a group of stars forming a recognizable pattern in the sky.
Examples: Orion and Great Bear.
Draw sketches to show the relative position of prominent stars in (a) Ursa Major (b) Orion.
(a) Ursa Major is in the northern sky; its main stars form a shape like a big ladle or saucepan.
(b) Orion lies near the celestial equator; three bright stars in a line form Orion’s belt in a hunter‑like pattern.
Name two objects other than planets that are members of the solar system.
(i) The Sun (a star made of hot gases, at the centre of the solar system).
(ii) Asteroids (small, rocky bodies that orbit the Sun, mainly between Mars and Jupiter).
Explain how you can locate the Pole Star with the help of Ursa Major.
In Ursa Major, take the two stars at the end of the “bowl” of the ladle and draw an imaginary straight line through them. Extend this line towards the north; the bright star lying on this line is the Pole Star.
Do all the stars in the sky move? Explain.
The stars are almost fixed relative to one another, but due to Earth’s rotation from west to east, they appear to move from east to west. The Pole Star lies nearly above Earth’s axis, so it appears almost stationary.
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?
Distances between stars are extremely large, so using kilometres gives very big numbers. Instead, we use the unit light year, which is the distance travelled by light in one year.
Numerically, 1 light year = 9.46 × 10¹² km.
If a star is eight light years away, its distance is:
Distance = 8 × 9.46 × 10¹² km = 7.568 × 10¹³ km.
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?
Let radius of Earth = Rₑ, radius of Jupiter = Rⱼ.
Given: Rⱼ = 11 Rₑ.
Volume of a sphere of radius r is V = (4/3) π r³.
Volume of Earth: Vₑ = (4/3) π Rₑ³.
Volume of Jupiter: Vⱼ = (4/3) π (11 Rₑ)³.
Now, (11 Rₑ)³ = 11³ · Rₑ³ = 1331 · Rₑ³.
So, Vⱼ = (4/3) π · 1331 · Rₑ³.
Ratio of volumes:
Vⱼ / Vₑ = [ (4/3) π · 1331 · Rₑ³ ] ÷ [ (4/3) π · Rₑ³ ] = 1331.
Therefore, the ratio of the volumes of Jupiter and Earth is 1331 : 1. Jupiter can accommodate about 1331 Earths in volume.
Boojho made the following sketch of the solar system. Is the sketch correct? If not, correct it.
The sketch is not correct because:
(a) Mars and Venus are interchanged; Venus should be closer to the Sun (between Mercury and Earth) and Mars farther out (after Earth).
(b) Uranus and Neptune are interchanged; Neptune should be the outermost planet.
(c) The asteroid belt should lie between Mars and Jupiter, not between Jupiter and Saturn.
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