Solved examples for class 8 science : Chapter 17
Star and Solar System
I. Multiple Choice Questions (MCQs).
Q.1. Generally the shapes of most of the galaxies are
c) either (a) or (b)
d) none of these
Answer. c) either (a) or (b)
Q.2. Within two weeks we see more than half of the moon, is called :
a) gibbous moon
b) crescent moon
c) waning of moon
d) none of these
Answer. (a) gibbous moon
Q.3. Which type of celestial objects have a head and a tail?
Answer. (c) Comets
Q.4. Hunter is a
a) natural satellite
Answer. (b) constellation
Q.5. Halley’s comet is visible after:
a) 75 years
b) 67 years
c) 76 years
d) 66 years
Answer. c) 76 years
II. Fill in the blanks by selecting appropriate words from the given list:
List : Galaxies, nebulae, Meteorites, Supercluster, celestial
Q.1. The stars, the moon, the planets and other objects in the sky are called ………………………….. bodies.
Q.2. ……………………………….are so big that it can take a ray of light thousands of years to travel across one.
Q.3. The milky way itself is only a tiny part of a group of galaxies called a ………………………. .
Q.4. New stars form within vast clouds of gas and dust, called …………………………….. .
Q.5. ………………………………..help scientists in investigating the nature of the material from which the solar system was formed.
III. Match the items of Column A with those of Column B.
Answer. 1-e, 2-a, 3-d, 4-b, 5-c
IV. Write ‘T’ for the true and ‘F’ for the false statements.
Q.1. The vast space which includes everything that exists on the earth and around it is called the universe.
Q.2. The first Indian satellite was ‘Aryabhatta’.
Q.3. Asteroids, comets and other small bodies come under the category of dwarf solar bodies.
Q.4. The tail of a comet always points towards the sun.
Q.5. Like venus, uranus also rotates from east to west.
Answer. 1-T, 2-T, 3-T, 4-F, 5- T
V. Very Short Answer Questions.
Q.1. Define crescent moon.
Answer. When only a part of the moon is illuminated by the sunlight, only the part towards the Earth is visible. In this position is called crescent moon.
Q.2. Why are many craters found on the surface of the moon?
Answer. Craters on the Moon are caused by asteroids and meteorites colliding with the lunar surface. The Moon’s surface is covered with thousands of craters. This is because the Moon has no atmosphere to protect itself from impacting bodies.
Q.3. Why can no one hear any sound on the moon?
Answer: Due to absence of atmosphere no one can hear any sound on the moon. Because sound need material medium for their propagation.
Q.4. Write classes of the planet and other bodies in the solar system (except satellite).
Answer: The planet and other bodies in the solar system are placed in three distinct classes : Planets, Dwarf planets and small solar system bodies.
Q.5. Which substances are present in the ring formed around the planet Saturn?
Answer. the ring formed around the planet Saturn is made of the ice and dust that surround the planet.
VI. Short Answer Questions.
Q.1. Why does the moon change its shape everyday?
Answer. Moon revolves around the earth. The earth revolves around the sun, i.e., the moon also revolves around the sun along with the earth. Moon is a non-luminous body. It does not produce its own light but it reflects sunlight towards earth. From earth we see only that part of the moon, from which the light of the sun is reflected towards earth. So, when seen from the Earth, the size and shape of moon appears to change periodically during its cycle. The day-to-day changes in the shape of the moon as seen from the earth is called phases of the moon.
Q.2. Why does the pole star appear stationary?
Answer. The pole star appears stationary because it lies on the imaginary axis of rotation of the earth.
Q.3. What are meteorites? How are they formed?
Answer. When a piece of meteor reaches the Earth, it is called meteorite. Meteors are very small stoneLike objects that are revolving around the sun. They become visible only when some of them enter by chance into the Earth’s atmosphere. When a meteor enters the atmosphere of the earth, it gets heated due to friction of air. The heat produced is so high that the meteor begins to glow and evaporates within a short time. Some meteors are so Large that a part of them reaches the surface of the earth before they get evaporated completely. In this way meteorites are formed.
Q.4. What do you mean by phases of the moon? Explain all the terms related to it.
Answer. The day-to-day changes in the shape of the moon as seen from the earth is called phases of the moon.
(i) The shape and size of the visible portion of the moon changes every day.
(ii) There are some days on which the shape of visible portion of the moon appears to perfectly round or nearly to perfectly round. The day on which the visible portion of the moon is perfectly round is known as the full moon day.
(iii) On the 8th day half portion of the moon appears in the sky. This is known as Waning.
(iv) On the 15th day the moon is not visible. This day is known as new moon day.
(v) On the 16th or 17th days, only a small portion of the moon is visible. This is known as Crescent moon.
(vi) Within two weeks we see more than half of the moon, it is called the Gibbous moon.
(vii) On the 29th days once again we get a full view of the moon. These various shapes all together are known as phases of the moon.
Q.5. Describe small solar system objects in your own words.
Answer. Asteroids, comets, meteors and meteorites revolve around the sun. These are also known as small solar system objects.
Asteroids :There is a large gap in between the orbits of the mars and Jupiter. The gap is occupied by a Large number of small bodies that revolve around the sun. These are called asteroids.
Meteors: These are very small stone-Like objects that are revolving around the sun. They become visible only when some of them enter by chance into the Earth’s atmosphere.
Comets: These are very small-sized celestial bodies that revolve around the sun in highly elliptical orbits. They become visible from the earth only when they come close to the sun.
Q.6. What do you understand by artificial satellites? Discuss uses of artificial satellites also.
Answer. Man-made object circulating around a planet is called its artificial satellite.
Artificial satellites are useful in the following ways:
i. They are used in weather forecasting.
ii. They are used in telephone communication.
iii. They are used in TV and radio transmission.
iv. They are used in locating mineral resources, underground water and for land mapping.
v. They are used in study and forecast the weather.
vi. They collect information from other planets and about the outer space.
VII. Long Answer Questions.
Q.1. What do you understand by constellations? Discuss some important constellations. Ans: Many of the stars seem to form a recognizable pattern in the night sky. These are called constellations.
Some important constellations are
(i) Ursa Major: It is also called the Great Bear. One part of the Ursa Major consisting of seven stars is fairly easy to spot in the night sky. This group of stars is called the Big Dipper or Vrihat Saptarshi.
(ii) Ursa Minor: It is also called the lesser Bear. One part of this constellation containing a group of seven stars is called the Little Dipper or Laghu Saptarshi.
(iii) Orion (or Mriga): Orion is also known as Kalpurush. There are seven bright stars and several faint stars in the Orion. The arrangement of stars in Orion looks like a hunter, with a bow.
(iv) Cassiopeia: It is a group of five stars forming W-Like shape, as given in the figure below. Its Indian astronomical name is Sarmistha. It is seen near the Pole star and is best visible in the month of October in the north sky.
(v) Pleiades: Pleiades is an important constellation in the sky. The stars in this constellation do not have any recognisable shape. It looks like a cluster of stars and twinkling gems in the night sky. The clusters of stars in this constellation are called globular clusters.
Q.2. (a) What do you mean by the solar system?
(b) Discuss some of the important features of the sun.
Answer. a) The sun and all the celestial bodies that revolve around it is known as solar system. It consists of large number of bodies such as planets, comets, asteroids and meteors. Now there are eight planets in the solar system. In the order of their distance from the Sun, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto and Xena (2003 UB313) come under the category of dwarf planets. Asteroids, comets and other small bodies come under the category of small solar bodies.
b) The sun is the centre of the solar system. Its features are as follows:
• It is our nearest star and compared to other stars, is of average size, mass and brightness. It looks bright and big only because it is closer to us than the other stars.
• Like all stars, the sun is a massive ball of exploring gas. Inside, tiny particles, called atoms of hydrogen gas join together to form another gas called helium. This joining process is called nuclear fusion and gives off huge amount of heat and light. This is sunshine. Without it, life cannot exist on the earth.
• The sun measures about 1.4 million kilometres from the earth. Inside, it could hold more than a million of planets as the size of the earth. But compared with the size of the some of the other stars in the universe, the sun is not all that big.
Q.3. Describe planets in your own words.
Answer. In the night sky, planets appear as bright specks of light much like stars. They do not twinkle. While the stars show no visible change in their position in the sky, the planets seen to move or wander with respect to the stars. That is why they were named planets.
Unlike stars, planets do not emit light of their own. They appear bright like stars in the night sky because they reflect light from the sun. They are also closer to us than the stars. Therefore, the light coming to us from the planets is brighter and bigger. Hence, they do not twinkle.
In the night sky Mercury, Venus, Mars, Jupiter, and Saturn look quite bright. They can be seen with naked eye. Uranus and Neptune can be seen only with a telescope.
All planets have definite paths in which they revolve around the sun. These paths are called orbit. The time taken by a planet to complete one revolution is called its period of revolution. As the distance of the planets increases from the sun, period of revolution also increases.