NCERT Q&A for Class 8 Science Chapter 17 Stars and The Solar System
1. In which part of the sky can you find Venus if it is visible as an evening star?
Soln:
The planet Venus is found in the western part of the sky after sunset and is said to be known as an evening star.
2. Name the largest planet of the solar system.
Soln:
Jupiter is the largest planet of the solar system.
3. What is a constellation? Name any two constellations.
Soln:
The group of stars that forms a recognizable pattern in the sky is known as a constellation.
Two constellations are; Ursa Major and Orion
4. Name two objects other than planets which are members of the solar system.
Soln:
a) Meteors
Meteors are small celestial objects that are seen as bright streaks of light in the sky. Due to the heat produced by the friction of the Earth’s atmosphere, the Meteors are burnt out while entering in. This causes the bright streaks in the sky. They are not planets.
b) Asteroids
The Asteroids are a collection of a huge number of small objects; gases and dust revolving around the sun. Between the orbits of Mars and Jupiter, they occupy the large gap. These are not planets. They are the celestial bodies and are known as Asteroids.
5. Do all the stars in the sky move? Explain.
Soln:
No, the earth rotates on its axis from west to east. Therefore, all the stars in the sky (except the pole star) seem to move from east to west. With reference to Earth, pole star in the sky does not seem to move because it is located above the axis of rotation of the Earth in the north direction. It seems to remain stationary at a point in the sky.
6. 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?
Soln:
The distance of the star from the earth and the distance between the stars is very huge. It is troublesome to express this distance in kilometre (km). Therefore, these huge distances are expressed in light-years. One light-year is equal to the distance travelled by the light in one single year. One light-year is equal to 9.46 x 1012 km.
A distance of the star from the Earth is eight light-years. This means the distance between them is equal to the distance travelled by the light in eight years, i.e. distance of the star is 8 x (9.6 x 1012) = 7.6 x 1013 km away from Earth.
7. 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?
Soln:
Let us consider Jupiter and Earth are two spheres with radii R and R,’ respectively. Given in the question that radius of Jupiter is 11 times the radius of the Earth.
So, R’= 11R
Volume of sphere of radius r is given as = 4⁄3πr3
Volume of Earth = 4⁄3πr3
And, volume of Jupiter = π(R1)3
=4⁄3 π(R1)3=1331[4/3πR3]
The ratio of the volume of Jupiter and Earth
=volume of Jupiter volume of Earth =1331(4/3πR3)4/3πR3=1331
Therefore, this ratio suggests that Jupiter can fit 1331 number of Earth in it.