CBSE Class 8 Science Stars and the Solar System Chapter Notes

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This Class 8 Science chapter note on Stars and the Solar System covers the universe, light years, stars, galaxies, constellations such as Ursa Major, Orion and Cassiopeia, the planets of the solar system, asteroids, comets and artificial satellites, along with the basics of nuclear energy, nuclear fission, the chain reaction and nuclear fusion. It ends with 97 multiple choice questions and their answers for revision.

THE UNIVERSE AND LIGHT YEAR

1. Universe is a vast collection of stars, planets, nebulae, galaxies, intergalactic matter and everything that exists in them. It is believed to be formed 15 billion years ago from a huge explosion called 'Big Bang'.
2. To measure distances on astronomical scale, the unit 'light year' is used. It is the distance travelled by light in one year. 1 light year = 9.46 × 10¹² km.

STARS AND GALAXIES

1. Stars are self-luminous astronomical bodies which produce energy from nuclear fusion reactions. They form from a large collection of gases, called a nebula.
2. A galaxy is a group of billions of stars and other celestial bodies. Galaxies exist in different shapes such as circular, elliptical, ring and irregular. They usually revolve around themselves and move away from each other at tremendous speeds.
3. A group of stars which seem to form a pattern is called a constellation. Examples: Big Bear, Orion etc.

CONSTELLATIONS

The group of stars which appears to form some recognisable shape or pattern is known as a constellation. Each constellation has been given a name signifying an animal, a human being or some other object which appears to resemble it. All the constellations appear to move in the sky from east to west. This is because the earth rotates on its axis from west to east. Some of the important constellations are: (i) Ursa Major (ii) Orion (iii) Cassiopeia (iv) Leo Major.

(i) Ursa Major
a) Ursa Major is one of the most famous constellations which can be seen in the night sky. It is also known as 'Great Bear', 'Big Bear', 'Big Dipper' or Plough.
b) The Ursa Major constellation consists of seven bright stars which are arranged in a pattern resembling somewhat a big bear.
c) The Ursa Major constellation is visible during the summer season.
d) We can locate the position of the Pole Star in the night sky with the help of Ursa Major.
e) Imagine a straight line through the two pointer stars of the Ursa Major constellation. This imaginary line towards the north direction in the sky is used to locate a bright star called the Pole Star.

[Figure: Ursa Major Constellation, a photograph-style illustration of a bear pattern formed by joined bright stars. Caption: Ursa Major Constellation]

(ii) Orion Constellation
a) The Orion constellation consists of seven or eight stars (and several faint stars).
b) The arrangement of stars in the Orion constellation is supposed to resemble a 'hunter' in the kneeling position. The star marked 1 in the figure represents the head of the hunter.
c) The stars marked 2 and 3 represent the shoulders. The stars marked 7 and 8 are imagined to be the feet of the hunter. The three stars in the middle, marked 4, 5 and 6, represent the belt of the hunter.
d) The Orion constellation is visible in the sky during the winter season.
e) The brightest star in the night sky, called 'Sirius', is located close to the Orion constellation.

(iii) Cassiopeia Constellation
a) Cassiopeia is another prominent constellation in the northern sky. It consists of 5 main stars.
b) The 5 main stars of the Cassiopeia constellation are arranged to form the shape of a distorted letter 'W' or 'M'.
c) The Cassiopeia constellation is visible during winter in the early part of the night.

THE SOLAR SYSTEM

Sun along with its nine planets, their satellites, asteroids and comets are together named as the solar system.

Mercury
i) Mercury is the closest planet to the Sun. It is the smallest in size compared to other planets of the solar system.
ii) It is very near to the Sun, so it can be seen from the Earth only occasionally after sunset and before sunrise. This is because Mercury is most of the time hidden by the glare of the Sun.
iii) Mercury's orbit is elliptical or more likely oval. Since it is closest to the Sun, it revolves around the Sun fastest.
iv) It has no natural satellite.

Venus
i) Venus is the second planet in terms of distance from the Sun.
ii) Venus is surrounded by thick clouds, so it reflects the light of the Sun from its surface. So it is the brightest planet of the solar system.
iii) Venus has a thick and dense atmosphere which mainly contains carbon dioxide. So it traps all the heat rays from the Sun (due to the greenhouse effect). The nearness of the Sun along with its heating caused by the greenhouse effect makes Venus the hottest planet of the solar system.
iv) The planet Venus can be seen either as a Morning Star in the eastern sky just before sunrise or as an Evening Star in the western sky just after sunset.

Earth
i) Our own planet Earth is the third planet of the solar system and is the only planet in the solar system on which life is known to exist.
ii) The environmental conditions on Earth which are responsible for the existence and continuation of life are as follows:
a) The Earth has an atmosphere which contains many gases including oxygen and carbon dioxide.
b) The Earth has large quantities of water which helps in the evolution and maintenance of life.
c) The Earth has a suitable temperature range for the existence of life.
d) The Earth has a protective blanket of ozone layer that absorbs extremely harmful ultraviolet radiations coming from the Sun.
iii) The Earth rotates about an imaginary axis that passes through its poles and is tilted at an angle of 23½°. This tilt of the Earth on its axis gives rise to the change of seasons.
iv) The Earth has only one natural satellite, the Moon.

Mars
i) Mars is seen in the sky as a reddish planet.
ii) Of all the planets, Mars is most like the Earth.
iii) Mars has a very thin atmosphere of traces of carbon dioxide, nitrogen, hydrogen and oxygen.
iv) It is a cold planet.
v) Mars has two moons, Deimos and Phobos.

Jupiter
i) Jupiter is the biggest planet of the solar system.
ii) The diameter of Jupiter is 11 times the diameter of the Earth and its mass is about 318 times that of the Earth. Jupiter is so large that about 1300 Earths can be placed inside this giant planet.
iii) Jupiter is made mainly of hydrogen and helium. Life cannot exist on Jupiter because it is a cold planet, and its atmosphere contains poisonous gases such as methane and ammonia.
iv) Jupiter has rings, but they are much fainter and smaller than those of Saturn.
v) It has 63 moons.

Saturn
i) Saturn is the second largest planet of the solar system.
ii) The most distinguishing feature of Saturn is the system of colourful rings which surround it.
iii) Saturn is the least dense among all the planets of the solar system.
iv) Saturn has 31 satellites.

Uranus
i) Uranus is the third biggest planet of the solar system.
ii) The most remarkable feature of Uranus is its highly tilted axis of rotation. As a result, Uranus appears to roll on its side while orbiting around the Sun.
iii) Uranus has 21 satellites.

Neptune
i) Neptune is the eighth planet of the solar system.
ii) It is an extremely cold planet.
iii) Neptune has eight satellites.

TERRESTRIAL AND GAS PLANETS

Because of their earth-like internal structure, Mercury, Venus, Earth and Mars are called terrestrial planets. Since Jupiter, Uranus, Saturn and Neptune are made up mainly of gases, they are called gas or Jovian planets.

ASTEROIDS, COMETS AND SATELLITES

1. Asteroids are irregular rocky bodies that revolve around the Sun between the orbits of Mars and Jupiter.
2. A comet is a small body of rocks, ice and gases that revolves around the Sun in a highly eccentric elliptical orbit.
3. A man-made spacecraft orbiting around an astronomical body is called a satellite. If the orbit of a satellite is synchronised with the Earth's rotation, it is called a geostationary satellite. If a satellite seems to be stationary from the point of view of the Sun, it is called a sun synchronous or polar satellite.
4. Satellites are used for communications, weather forecasting, remote sensing, conducting scientific experiments and for various other military uses.

NUCLEAR ENERGY

Energy released when some changes take place in the nucleus of an atom is called nuclear energy. During the phenomenon of radioactivity, a heavy atom gets split into a number of light atoms. The total mass of the products is less than the mass of the original atom. Thus there is a loss of mass, which gets converted into energy. The energy emitted in this process is known as nuclear energy.

Energy of particles and radiation emitted are measured in units known as electron volts (eV).
1 eV = 1.602 × 10^-19 joules
1 atomic mass unit (u) = 931 million electron volts of energy, that is 1 u = 931 MeV.

Types of Nuclear Energy
The energy stored in the nucleus of an atom can be obtained by either of two processes: (i) nuclear fission and (ii) nuclear fusion.

Nuclear Fission: Nuclear fission is the process of breaking of a heavy nucleus (like that of uranium) into two medium sized nuclei with the liberation of energy. It is carried out by bombarding the heavy nucleus with low energy neutrons. A neutron is a neutral particle, so it can enter the nucleus easily. When U-235 is bombarded with neutrons, the uranium nucleus disintegrates into smaller nuclei of lighter elements. The neutrons that produce fission have low energy and are called thermal neutrons or low energy neutrons.

Figure: Nuclear fission

Reaction: The uranium nucleus can split up in a number of ways, giving different fission products. Each time a uranium nucleus breaks, it releases 2 to 3 neutrons. The process also depends on the projectile and its energy. A common fission reaction of the uranium-235 isotope with thermal neutrons is:

²³⁵₉₂U + ¹₀n → ⁹⁴₄₂Mo + ¹⁴⁰₅₇La + 2 ¹₀n + β rays + E.E.

In this reaction a tremendous amount of energy is released. This energy is due to the mass defect, that is the difference in mass Δm between the original nucleus and the product nuclei. The loss of mass Δm is converted into energy E according to Einstein's mass energy equation:
E = Δm c²
where c is the speed of light in vacuum. When ²³⁵₉₂U is bombarded by a thermal neutron, each atom of uranium-235 releases 200 MeV of energy and 2 to 3 neutrons.

Comparison of Energy Produced by Nuclear Fission with Coal: During the process of nuclear fission, one atom of uranium produces 200 MeV of energy, which is 10 million times the energy produced by the combustion of an atom of carbon from coal.

Nuclear Fission Reaction is a Chain Reaction: During the fission of a uranium atom, 2 to 3 neutrons are produced. Each neutron possesses about 2 MeV of energy, which is much more than the energy of the thermal neutrons that started the fission. The energies of these neutrons can be reduced to thermal neutron energy (about 0.025 MeV) by surrounding the fissile material with a special substance known as a moderator. The moderator slows down the fast moving neutrons. Now each neutron released causes further fission and releases more energy and more neutrons. This process continues, and about 10²⁴ fission reactions take place in about one millionth of a second. As a result, a tremendous amount of energy is released in a fraction of a second. This reaction is called a chain reaction.

[Figure: The nuclear fission chain reaction: a neutron strikes a U-235 nucleus, which splits and releases neutrons that strike further U-235 nuclei, with the reaction spreading in several generations; the figure is labelled 'The nuclear fission (chain reaction)']

A reaction in which the particle which starts the reaction is also produced back during the course of the reaction, and the reaction continues to take place, is called a chain reaction.

Nuclear Fusion
In a nuclear fission reaction a heavy nucleus splits into two lighter nuclei and energy is released. Conversely, when two light nuclei combine or fuse to form a bigger nucleus, a tremendous amount of energy is also released. This process is called nuclear fusion, and it is another way of generating energy from the nucleus of an atom. For example, when two hydrogen isotopes combine, a nucleus of helium is produced:

²₁H + ²₁H → ³₂He + ¹₀n + Energy (3.3 MeV)

During nuclear fusion the loss of mass, or mass defect, is more than that in fission. This loss of mass is converted into a large amount of energy. It is estimated that the energy released during fusion is 10 times more than that released during fission.

Conditions required for the fusion reaction:
1. The nuclei should be very light.
2. The nuclei must have high kinetic energies. This can be achieved by:
i) Using a particle accelerator: the projectiles are accelerated in a particle accelerator and made to strike the target nuclei.
ii) Increasing the temperature of the nuclei: the temperature should be at least 10⁶ K, so that the positively charged nuclei overcome the electrostatic force of repulsion between them. The fusion reactions carried out at extremely high temperature are called thermonuclear reactions.

Fusion reaction on the surface of the Sun: Thermonuclear reactions are the source of energy of the Sun and other stars. Hydrogen nuclei present in the Sun, at very high temperature (millions of degrees) and millions of Pascals of pressure, fuse together to form helium.

Example of nuclear fusion.

Hydrogen Bomb: A hydrogen bomb is based on the thermonuclear fusion reaction. It contains a mixture of deuterium (²₁H), tritium (³₁H) and lithium (⁶Li) in suitable proportions, coupled with an atomic bomb. When the temperature of this mixture is raised to 10⁷ K in a few microseconds, it triggers the fusion of hydrogen with the release of very high energy in a short time.

MULTIPLE CHOICE QUESTIONS

1. Live telecast of a cricket match is possible due to
(A) geostationary satellite
(B) polar satellite
(C) low-earth orbiting satellite
(D) sum-synchronous satellite

Answer: (A) geostationary satellite

2. Satellites revolve in
(A) circular and hyperbolic orbits
(B) elliptical and parabolic orbits
(C) circular and elliptical orbits
(D) only in elliptical orbits

Answer: (C) circular and elliptical orbits

3. A spy satellite is depolyed in
(A) low-earth orbit
(B) geostationary orbit
(C) both A and B
(D) none of the above

Answer: (A) low-earth orbit

4. Ceres is
(A) satellite of the Mars
(B) satellite of the Jupiter
(C) an asteroid
(D) a meteorite that fell over Siberia in 1908

Answer: (C) an asteroid

5. Name the biggest planet.
(A) Uranus
(B) Jupiter
(C) Neptune
(D) Mars

Answer: (B) Jupiter

6. Name the farthest planet from the earth.
(A) Mercury
(B) Pluto
(C) Neptune
(D) Sometimes Pluto and at other times Neptune

Answer: (D) Sometimes Pluto and at other times Neptune

7. The orbits of which two planets intersect with each other?
(A) Mercury and Venus
(B) Mars and Jupiter
(C) Uranus and Neptune
(D) Neptune and Pluto

Answer: (D) Neptune and Pluto

8. Name the brightest non-star visible to human eye.
(A) Moon
(B) Venus
(C) Mars
(D) Jupiter

Answer: (A) Moon

9. Brightest planet visible to naked eye is
(A) Venus
(B) Mars
(C) Jupiter
(D) Mercury

Answer: (A) Venus

10. The largest satellite in the solar system is
(A) Moon
(B) Io
(C) Eros
(D) Ganymede

Answer: (D) Ganymede

11. The planet also know as red planet is
(A) Mars
(B) Venus
(C) Earth
(D) Jupiter

Answer: (A) Mars

12. Other than the earth, which other planet has the thick atmospheric layer to absorb harmful ultraviolet rays?
(A) Mars
(B) Jupiter
(C) Venus
(D) Mercury

Answer: (C) Venus

13. The planet also known as “morning star” is
(A) Mars
(B) Mercury
(C) Jupiter
(D) Venus

Answer: (D) Venus

14. Name the space telescope which was put into orbit in 1990.
(A) INSAT
(B) Aryabhatta
(C) Sputnik
(D) Hubble

Answer: (D) Hubble

15. Which of the following planets can be seen with naked eye?
(A) Mercury, Venus; Uranus, Jupiter
(B) Mars, Jupiter, Uranus, Neptune
(C) Mercury, Venus, Uranus, Pluto
(D) Mercury, Mars, Venus, Jupiter

Answer: (D) Mercury, Mars, Venus, Jupiter

16. Where do you find the “sea of tranquility”?
(A) Moon
(B) Earth
(C) Mercury
(D) Mars

Answer: (A) Moon

17. Which planet has “the great red spot”?
(A) Mars
(B) Venus
(C) Jupiter
(D) Mercury

Answer: (C) Jupiter

18. Name the hottest planet in the solar system.
(A) Mercury
(B) Venus
(C) Earth
(D) Mars

Answer: (B) Venus

19. The biggest of all constellations is
(A) Sirius
(B) Hydra
(C) Andromeda
(D) Ursa minor

Answer: (B) Hydra

20. The space vehicle used to send men on to the moon is
(A) Gemini
(B) Apollo
(C) Sputnik
(D) Discovery

Answer: (B) Apollo

21. Mercury is closer to the sun than the Venus. But Venus is hotter than Mercury. Give reason.
(A) Mercury has no atmosphere and Venus has a thick atmosphere which can retain the heat
(B) Mercury is mostly made up of sedimentary rocks while Venus contains igneous rocks
(C) Mercury being closer to the sun, sun absorbs the heat of the Mercury
(D) All the above

Answer: (A) Mercury has no atmosphere and Venus has a thick atmosphere which can retain the heat

22. Ozone is a compound containing
(A) oxygen
(B) nitrogen
(C) carbon
(D) carbon and oxygen

Answer: (A) oxygen

23. Ozone is present in
(A) troposphere
(B) stratosphere
(C) ionosphere
(D) ozonosphere

Answer: (B) stratosphere

24. The first man to land on the moon is
(A) Rakesh Sharma
(B) Kalpana Chawla
(C) Yuri Gagarin
(D) Neil Armstrong

Answer: (D) Neil Armstrong

25. The number of satellites of Venus is
(A) one
(B) two
(C) three
(D) zero

Answer: (D) zero

26. Expand ISRO.
(A) International Society for Research on Optometry
(B) Indian Satellite and Radar Organisation
(C) Indian Space Research Organization
(D) Indian Stratosphere Resourcing Organisation

Answer: (C) Indian Space Research Organization

27. Lunar eclipse occurs on
(A) full moon day
(B) new moon day
(C) both the above
(D) none of the above

Answer: (A) full moon day

28. Smallest planet is
(A) Mercury
(B) Mars
(C) Pluto
(D) Moon

Answer: (A) Mercury Pluto is now classified as a dwarf planet, so Mercury is the smallest planet.

29. Halley is the name of a/an
(A) comet
(B) asteroid
(C) satellite of Jupiter
(D) meteorite

Answer: (A) comet

30. The tail of a comet usually extends to
(A) 10 kilometres
(B) 2 light years
(C) 25 million kilometres
(D) 1.5 billion kilometres

Answer: (C) 25 million kilometres Comet tails often extend tens of millions of kilometres.

31. The closely packed part of the comet which contains solid particles, stones and frozen water is called
(A) coma
(B) nucleus
(C) tail
(D) orbit

Answer: (B) nucleus

32. Sphere of microscopic dust surrounding the nucleus of a comet is called
(A) coma
(B) tail
(C) tail
(D) nucleon

Answer: (A) coma

33. The height of low-earth satellites ranges between
(A) 300 - 800 km
(B) 20 - 80 km
(C) 36,000 km
(D) 200 - 7200 km

Answer: (A) 300 - 800 km

34. GPS means
(A) Global Positioning System
(B) Geometrical Processing Satellite
(C) Gestalt Psychological Synchronisation
(D) none of the above

Answer: (A) Global Positioning System

35. GSLV means
(A) Geostationary Satellite Launch Vehicle
(B) German Satellite Launching Vehicle
(C) Global Satellite Locus Verification System
(D) none of the above

Answer: (A) Geostationary Satellite Launch Vehicle

36. In the sun
(A) hydrogen is converted to helium
(B) helium is converted to hydrogen
(C) hydrogen is converted to uranium
(D) all the above

Answer: (A) hydrogen is converted to helium

37. Solar system was formed
(A) 16 billion years ago
(B) 4.5 billion years ago
(C) 10 billion years ago
(D) 11.5 billion years ago

Answer: (B) 4.5 billion years ago

38. Solar eclipse occurs on
(A) full moon day
(B) new moon day
(C) both the above
(D) none of the above

Answer: (B) new moon day

39. Lunar eclipse occurs when the
(A) sun comes between the earth and the sun
(B) moon comes between the earth and the sun
(C) earth comes between the moon and the sun
(D) when the earth and moon collide with each other

Answer: (C) earth comes between the moon and the sun

40. Solar eclipse occurs when the
(A) sun comes between the earth and the moon
(B) moon comes between the earth and the sun
(C) earth comes between the moon and sun
(D) none of the above

Answer: (B) moon comes between the earth and the sun

41. Who mathematically proved that the planets revolve around the sun in elliptical orbits?
(A) Isaac Newton
(B) Albert Einstein
(C) Johannes Kepler
(D) Galilei Galileo

Answer: (C) Johannes Kepler

42. One cosmic year is equal to
(A) 365 days
(B) 24 days
(C) 2.25 x 10⁶ days
(D) 225 x 10⁶ years

Answer: (D) 225 x 10⁶ years

43. Cosmic year is
(A) the time taken by the earth to revolve around the sun
(B) the time taken by the sun to revolve around itself
(C) the time taken by the earth to revolve around itself
(D) the time taken by our milky way galaxy to revolve around itself

Answer: (D) the time taken by our milky way galaxy to revolve around itself

44. Between 1979 and 1999, the farthest planet from the sun is
(A) Pluto
(B) Neptune
(C) Uranus
(D) Planet

Answer: (B) Neptune

45. The nearest galaxy to our galaxy is
(A) Andromeda
(B) X31
(C) Large magellanic cloud
(D) Small magellanic cloud

Answer: (C) Large magellanic cloud It lies about 160,000 light years away, much closer than Andromeda.

46. The planet which takes the maximum time to revolve around the sun is
(A) Mars
(B) Pluto
(C) Neptune
(D) Uranus

Answer: (B) Pluto

47. The planet which takes the maximum time to revolve around itself is
(A) Mercury
(B) Pluto
(C) Venus
(D) Neptune

Answer: (C) Venus

48. Light year is a unit of
(A) time
(B) intensity of light
(C) illuminance
(D) distance

Answer: (D) distance

49. The speed of light in vacuum is
(A) 330 m/s
(B) 300,000 m/s
(C) 300,000 km/s
(D) 1759 m/s

Answer: (C) 300,000 km/s

50. Stars produce energy by
(A) burning coal
(B) burning petroleum
(C) nuclear reactions
(D) both A and B

Answer: (C) nuclear reactions

51. Name the closest star to our solar system other than the sun.
(A) Proxima centauri
(B) Sirius
(C) Swati
(D) Ashwini

Answer: (A) Proxima centauri

52. Stars are mainly made up of
(A) oxygen and hydrogen
(B) oxygen and nitrogen
(C) hydrogen and helium
(D) water and helium

Answer: (C) hydrogen and helium

53. A group of stars which seem to form a pattern is called
(A) nebula
(B) galaxy
(C) asteroid
(D) constellation

Answer: (D) constellation

54. Galaxies
(A) move toward each other
(B) move away from each other
(C) do not move at all
(D) none of the above

Answer: (B) move away from each other

55. A meteoroid that falls on the earth is called
(A) asteroid
(B) comet
(C) meteor
(D) meteorite

Answer: (D) meteorite

56. Which of the following has a highly elongated elliptical orbit?
(A) Asteroid
(B) Meteor
(C) Comet
(D) Meteorite

Answer: (C) Comet

57. The approximate height of a geostationary satellite is
(A) 6400 km
(B) 12,800 km
(C) 7200 km
(D) 36,000 km

Answer: (D) 36,000 km

58. The first Indian satellite is
(A) INSAT
(B) Aryabhatta
(C) Ehaskara
(D) APPLE

Answer: (B) Aryabhatta

59. Expand ISS
(A) International Space Station
(B) International Space Society
(C) Indian Space Station
(D) Internet Society for Semantics

Answer: (A) International Space Station

60. Jupiter is a/ an
(A) terrestrial planet
(B) gas planet
(C) asteroid
(D) hottest planet

Answer: (B) gas planet

61. The coldest planet is
(A) Mercury
(B) Neptune
(C) Pluto
(D) Jupiter

Answer: (B) Neptune Pluto is now classified as a dwarf planet, so Neptune is the coldest planet among the options.

62. All stars appear to move from
(A) east to west
(B) west to east
(C) north to south
(D) south to north

Answer: (A) east to west

63. Pole star appears to be stationary in all seasons because
(A) pole star does not rotate on its axis
(B) pole star happens to lie on the axis of equator
(C) pole star happens to lie above the axis of north pole of the earth
(D) pole star is most distant of all the stars

Answer: (C) pole star happens to lie above the axis of north pole of the earth

64. Stars appear to move from east to west because
(A) stars actually move from east to west
(B) stars actually move from west to east
(C) earth rotates in west to east direction
(D) earth rotates in east to west direction

Answer: (C) earth rotates in west to east direction

65. Orion is a name of
(A) star
(B) planet
(C) galaxy
(D) constellation

Answer: (D) constellation

66. The force that is responsible for the rotation of the earth around the sun is
(A) electric force
(B) magnetic force
(C) electromagnetic force
(D) gravitational force

Answer: (D) gravitational force

67. Polar satellite orbits around
(A) poles
(B) north pole
(C) south pole
(D) equator

Answer: (A) poles

68. The planet of the solar system having no satellite
(A) Jupiter
(B) Venus
(C) Saturn
(D) Mars

Answer: (B) Venus

69. One light year is equal to
(A) 9.46 × 10¹² m
(B) 9.46 × 10¹⁰ m
(C) 9.46 × 10¹⁰ km
(D) 9.46 × 10¹² km

Answer: (D) 9.46 × 10¹² km

70. The time taken by light to reach the earth from the sun is
(A) 200 s
(B) 300 s
(C) 400 s
(D) 500 s

Answer: (D) 500 s

71. Asteroids are located between
(A) The Earth and the Mars
(B) The Mars and Jupiter
(C) Jupiter and Saturn
(D) The Mercury and the Venus

Answer: (B) The Mars and Jupiter

72. The Milky way Galaxy is the example of a
(A) Spiral galaxy
(B) Elliptical galaxy
(C) Irregular galaxy
(D) Circular galaxy

Answer: (A) Spiral galaxy

73. The constellation which moves around the pole star is
(A) Cassiopeia
(B) Orion
(C) Big bear
(D) Plcides

Answer: (C) Big bear

74. The scientist who proposed the big bang theory regarding the origin of universe was
(A) Galileo
(B) Archimedes
(C) Edwin Hubble
(D) Halley

Answer: (C) Edwin Hubble

75. Shooting star is another name for
(A) Comet
(B) Meteor
(C) Solar flare
(D) Nebulae

Answer: (B) Meteor

76. The part of a meteor which reaches the Earth’s surface is called a
(A) Comet
(B) Meteor
(C) Solar flare
(D) Nebulae

Answer: (B) Meteor

77. What is the number of stars in the solar system?
(A) 1
(B) 5
(C) 9
(D) Much larger than 9

Answer: (A) 1

78. The ratio of earth’s gravity to sun’s gravity is
(A) 6
(B) 1/6
(C) 28
(D) 1/28

Answer: (D) 1/28

79. The planet nearest to the sun is
(A) Mercury
(B) Earth
(C) Venus
(D) Pluto

Answer: (A) Mercury

80. The planet farthest from the sun is
(A) Mercury
(B) Venus
(C) Pluto
(D) Earth

Answer: (C) Pluto

81. Shooting star is another name for
(A) comet
(B) meteor
(C) solar flare
(D) nebulae

Answer: (B) meteor

82. The part of a meteor which reaches the earth’s surface is called a
(A) comet
(B) meteorite
(C) shooting star
(D) nebule

Answer: (B) meteorite

83. The tail of a comet always points
(A) towards the sun
(B) away from the sun
(C) towards north-east
(D) towards south-west

Answer: (B) away from the sun

84. The star nearest to the sun is
(A) Siritus
(B) Proxima centauri
(C) Alpha centauri
(D) Cygni

Answer: (B) Proxima centauri

85. The colour of a star depends upon its
(A) density
(B) distance from the sun
(C) surface temperature
(D) radius

Answer: (C) surface temperature

86. Which of the following does not represent a cluster of stars?
(A) Rigel
(B) Aquarius
(C) Capricorn
(D) Aries

Answer: (A) Rigel

87. How many constellations comprise the signs of the zodiac?
(A) 6
(B) 9
(C) 11
(D) 12

Answer: (D) 12

88. Which of the following is a star?
(A) Sun
(B) Mercury
(C) Pluto
(D) Venus

Answer: (A) Sun

89. The planet having the largest number of satellites amongst the following is
(A) Jupiter
(B) Saturn
(C) Uranus
(D) Mars

Answer: (B) Saturn

90. Which of the following planets has the least number of satellites?
(A) Earth
(B) Neptune
(C) Uranus
(D) Mars

Answer: (A) Earth

91. Which of the following is a natural satellite of our planet?
(A) Moon
(B) Sun
(C) Jupiter
(D) Saturn

Answer: (A) Moon

92. Which of the following is the smallest planet?
(A) Jupiter
(B) Venus
(C) Mercury
(D) Pluto

Answer: (C) Mercury Pluto is now classified as a dwarf planet, so Mercury is the smallest planet.

93. Which of the following is the biggest planet?
(A) Jupiter
(B) Venus
(C) Mercury
(D) Pluto

Answer: (A) Jupiter

94. Any heavenly body having light of its own is called a
(A) nebulae
(B) star
(C) comet
(D) meteorite

Answer: (B) star

95. Any heavenly body which revolves round a planet is called
(A) comet
(B) star
(C) satellite
(D) nebulae

Answer: (C) satellite

96. How much time does light from the sun take to reach the surface of the earth?
(A) 400 s
(B) 500 s
(C) 450 s
(D) 55 s

Answer: (B) 500 s

97. Velocity of light is
(A) 3 × 10⁴ km/s
(B) 3 × 10⁶ km/s
(C) 3 × 10⁵ km/s
(D) 3 × 10³ km/s

Answer: (C) 3 × 10⁵ km/s

i) Ursa Major iii) Cassiopeia
iii) Orion iv) Leo Major