NCERT Solutions for Class 8th Science Chapter 15 Stars and the Solar system textual questions and answers based on the latest syllabus of CBSE and JKBOSE NCERT Books
Excercise of the Stars and the Solar system
1. Fill in the blanks by choosing correct words from the following list:
List: meteorite, pluto, moon, planets, universe, core, comet, constellation.
Answers:
1.1 The branch of science which deals with the study of universe is called astronomy.
1.2 The unburnt part of a meteor which reaches the earth is called meteorite.
1.3 The heavenly bodies which revolve around the sun are called planets.
1.4 The heavenly bodies which revolve around the planets are called moon.
1.5 The orbit of pluto is not in the same plane as that of the other planets.
1.6 A heavenly body with a long tail, moving around the sun in an elliptical path is called comet.
1.7 In the core of the sun, hydrogen gas fuses with the liberation of energy.
1.8 A group of stars which resembles an animal or some other known object is called constellation.
2. Statements given below are incorrect. Write the correct statements.
2.1 Halley’s comet visits our solar system after 26 years.
Correct Statement: Halley’s comet visits our solar system after 76 years.
2.2 Helium gas constitutes most of the atmosphere of the sun and the stars.
Correct Statement: Hydrogen gas constitutes most of the atmosphere of the sun and the stars.
2.3 Pole star is nearest to our solar system.
Correct Statement: Proxima Centauri is nearest to our solar system.
2.4 Astronomers have divided the sky into 68 constellations.
Correct Statement: Astronomers have divided the sky into 88 constellations.
2.5 Meteors on burning leave behind gold dust and light.
Correct Statement: Meteors on burning leave behind a trail of light and dust.
2.6 The orbit of Neptune is different from the orbits of the other planets in the solar system.
Correct Statement: The orbit of Pluto is different from the orbits of the other planets in the solar system.
2.7 Mars is the second planet nearest to the sun.
Correct Statement: Venus is the second planet nearest to the sun.
2.8 Moon revolves around the earth in 21½ days.
Correct Statement: Moon revolves around the earth in 27⅓ days.
3. Answer the following questions:
3.1 What is the universe? Name six different kinds of heavenly bodies found in the universe?
Answer:
The universe is the vast expanse of space that includes everything in existence, including stars, planets, galaxies, and all forms of matter and energy. Six different kinds of heavenly bodies found in the universe are stars, planets, moons, asteroids, comets, and meteoroids.
3.2 With reference to the average distance from the sun, state:
(a) the serial number of the planet Earth
(b) the average distance of the Earth from the sun
(c) the time in which the sunlight reaches the Earth
Answer:
(a) Earth is the third planet from the sun.
(b) The average distance of the Earth from the sun is about 149.6 million kilometers (93 million miles).
(c) The time in which the sunlight reaches the Earth is approximately 8 minutes and 20 seconds.
3.3 (a) Name the natural satellite of the Earth.
(b) In how many days does this satellite complete one revolution around the Earth?
(c) In how many days does this satellite rotate around its own axis?
(d) How does the gravity of this satellite compare with the Earth?
(e) State the maximum temperature on the day side and minimum temperature on the night side of this satellite.
Answer:
(a) The natural satellite of the Earth is the Moon.
(b) The Moon completes one revolution around the Earth in about 27⅓ days.
(c) The Moon rotates around its own axis in about 27⅓ days.
(d) The gravity of the Moon is about 1/6th that of the Earth.
(e) The maximum temperature on the day side of the Moon is about 127°C, and the minimum temperature on the night side is about -173°C.
3.4 What do you understand by the following terms:
(a) New Moon
(b) Full Moon
Answer:
(a) New Moon: The New Moon is the phase of the Moon when it is positioned between the Earth and the Sun, making it invisible from the Earth.
(b) Full Moon: The Full Moon is the phase of the Moon when it is opposite the Sun, fully illuminated and visible from the Earth.
3.5 (a) Define solar system.
(b) Name all the planets in the solar system in the order of their distance from the sun.
Answer:
(a) The solar system is a collection of celestial bodies, including the Sun, eight planets, their moons, and other objects like asteroids and comets, all bound by the gravitational force of the Sun.
(b) The planets in the solar system in order of their distance from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
3.6 (a) How many moons does Mars have?
(b) Write the name of these moons.
Answer:
(a) Mars has two moons.
(b) The names of Mars’ moons are Phobos and Deimos.
3.7 What is a comet? Why does a comet develop a tail while approaching the sun?
Answer:
A comet is a small icy celestial body that orbits the Sun. As a comet approaches the Sun, the heat causes its ice to vaporize and form a glowing tail of gas and dust particles.
3.8 What is a star? What makes the star give out a vast amount of energy?
Answer:
A star is a massive, luminous celestial body made of plasma that emits light and heat. The vast amount of energy from a star is produced through nuclear fusion, where hydrogen atoms combine to form helium, releasing energy.
3.9 (a) How are meteors different from stars?
(b) How are meteors different from meteorites?
Answer:
(a) Meteors are small particles from space that burn up upon entering the Earth’s atmosphere, appearing as streaks of light, while stars are massive, glowing celestial bodies that generate light through nuclear fusion.
(b) Meteors are the flashes of light caused by the burning of small particles entering the Earth’s atmosphere, whereas meteorites are the remnants of these particles that survive the atmospheric entry and reach the Earth’s surface.
