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THE UNIVERSE
THE UNIVERSE
INTRODUCTION
The plastic earth that we live on is a tiny speck in the vast surroundings space called ‘The Universe’.
The sun which sustains all life on our planet in only one of the innumerable stars which light up our night sky.
In this chapter we will study about stars, planets, satellites as well as earth from their birth to the inactive state
through the period of drastic changes.
IMPORTANT TERMS AND CONCEPTS
1.
The Universe. The vast space surrounding us is called universe. The universe includes everything that
exists–the most distant stars, planets, satellites, as well as own earth and all the objects on it.
2.
Light Year. It is the distance traveled by light in the one year is equal to 9.46 × 1012 kilometers.
It is the unit of distance.
1 light year = 300000 × 365 × 24 × 60 × 60 = 9.46 × 1012 km. The actual distance of the alpha centuari
in kilometers is (4.3 light years) 4.3 × 9.46 × 1012 km = 4.067 × 1013 km.
3.
Parsec. It is an astronomical unit of distance which is equal to 3.26 light years. 1 parsec = 3.26 light
years.
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Galaxy. A cluster or group of billions of stars is called galaxy Milky way galaxy, Andromeda galaxy.
There are about 100 billion galaxies (1011 galaxies) in the universe an each galaxy on an average has 100
billion stares (1011 stars) in the universe. So, the total number of stars in the universe is 1022 stars.
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Classification of Galaxies. Galaxies have many different shapes and sizes. The galaxies are usually
classified on the basis of their shape. The two most common shapes of galaxies are-Spiral and Elliptical.
Some of them have irregular shape, they are called irregulars galaxies. Thus, there are three types of
galaxies (i) Some galaxies (ii) Elliptical galaxies (iii) Irregular galaxies. They are shown in following
figures:
(a) Spiral galaxy
(b) Elliptical galaxy
Fig. 17.1 Different shapes of galaxies
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(c) Irregular galaxy
The Milky Way: Our own galaxy. Ours is the Milky Way galaxy. It is a spiral type of galaxy. We live
near the outer of Milky Way which is 1,00,000 light years in diameter and is slowly rotating. The view
of the Milky Way galaxy as seen from above is shown in the given fig. (a) which looks like disc of stars.
The stars are not uniformly distributed in the place of disc, but are arranged is spiral arms emerging
from the nucleus of the galaxy. The side view of Milky Way galaxy is shown in the given fig (b). In sky,
our galaxy appears like a river of light running from one corner to another. So it is called “Akash
Ganga”.
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THE UNIVERSE
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(a) Top view of Milky Way galaxy
(b) Side view of Milky Way galaxy
Fig. 17.2: The Milky Way galaxy.
The andromeda galaxy is one of the brightest and most accessible galaxy from Earth. It is about 2
million light years (2 × 106) from Earth. It is only half the size of our Milky Way galaxy.
Constellations. The stars which appear in the form of closed groups and form recognizable shapes and
patterns are known as constellation. Some of the important constellations. Some of the important
constellations are (i) Ursa Major (Great bear) ‘Saptarishi’ (ii) Ursa minor (Little bear), ‘Langhu
Saptarishi’ or ‘Dhruv Matsaya’ (iii) Orion (Hunter) ‘Vyadha’ or Mriga (iv) Scorpio ‘Vrishchika’ (v)
Pleides ‘Kruttika’ (vi) Cassiopeia – ‘Sarmishtha’.
(i) Ursa Major Constellation. The arrangement of stars is shown in the given figure. It reminds us of a
large ladle or a question mark studded in the sky. The ursa major is called great bear because its stars are
arranged is such a way that they also seem to form the outline of a big bear or great bear. It can be seen
clearly in April in summer season in the northern part of the sky at night. It is called summer
constellation.
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2
6
5
4
7
3
Fig. 17.3: Ursa Major or Great Bear
(ii) Ursa Minor Constellation (Little Bear Constellation). It is a close of seven stars. The arrangement
is similar to those in ursa, major, the only difference being that the stars in ursa minor are closed
together and appear to form the outline of a little bear. The stars in Ursa Minor are less bright than those
of Ursa Major. At the end of the tail of Ursa Minor is a very important star of average brightness which
is called pole star. The Ursa Minor constellation can see in the northern part of the sky in July during the
summer season.
Fig 17.4: Ursa Minor
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THE UNIVERSE
(iii) Orion constellation (Hunter constellation). The arrangement of stars in orion constellation is
supported to resemble a hunting stars are supposed to form of a hunter. The head and limbs of the hunter
are formed from other faint stars which are not shown in the given figure. The orion constellation is
visible during the winter season.
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Fig. 17.5: Orion Constellation
Scorpio Constellation. The arrangement of stars is the Scorpio constellation is as shown in the given
figure. The Scorpio constellation resembles a Scorpio (bichchhu) complete with tail and pincers. It is
usually visible in the summer season.
Fig. 17.6: The arrangement of stars in Scorpio Constellation
Pleides Constellation. It does not have specific arrangement of stars which can be compared to a
definite shape. It looks a cluster of twinkling gems in the night sky. The cluster of stars represented by
pleides constellation in called star cluster. It is visible in winter season. The Indian name is Kruttika.
Fig. 17.7: Pleides Constellation
Difference between a Galaxy and a constellation:
Galaxy
1. Galaxy is a collection of billion of stars
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Constellation
1. Constellation is a collection of only a few stars.
2. Galaxy does not form a definite pattern 2. Constellation resembles with a shape of human
resembling an animal or human being.
being or animal.
Stars. They are the heavenly bodies ike the sun that are extremely hot and have light of their own. They
are made up of vast of hydrogen gas, some helium and dust. Hydrogen atoms are being continuously
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converted into helium and a large amount of nuclear energy in the form of heat and light is released. The
stars are not permanent. They are born, mature, grow old and finally die.
Classification of stars. They are classified on the basis of four physical characteristics (i) size (ii) color
(iii) brightness (iv) temperature.
Pole star. The star which lies immediately above the earth’s north pole and around which all other stars
seem to revolve is called pole star. The Indian name of pole star is ‘Dhruv tara’. It appears to be
stationary in the sky and does not change its position at all. It has been observed that all the stars
including pole star, appear to move from east to west. Sun cannot be used to find direction, since it does
not rise exactly from east. So pole star is used as a reference to find direction.
Sun. The sun is also a star around which the earth and other planets revolve. The sun is small and of
average brightness as compared to other stars. The star appears to be larger and brighter because it is
much more nearer to the earth than any other star. It is nearer to us, therefore, it does not twinkle like
other stars. The temperature on the surface of sun is about 6000°C whereas the temperature of its center
is about 20 million degree Celsius. It is the main source of heat and light energy for all the members of
solar system. Sun also rotates about the center of galaxy with period 250 million years.
Mass of the sun is 1.98 × 1030 kg and its diameter is 13.9 × 108 m. It also rotates its own axis with a
period of 34 days at poles and 25 days at the equator. The luminous high pressure of the interior of sun
is called the photosphere. Surrounding the photosphere is the chromosphere at a temperature of 6000 K.
Sun at Solar Eclipse. Layers above the photosphere are extremely hot but densities are extremely low.
There are not visible is strong light from the disc of sun. During solar eclipse, when the sun’s disc is
completely covered, the outer-most layer becomes visible. This appears like a crown round the sun
called corona.
Energy of sun. The protons/hydrogen in sun combines to form a heavy helium nucleus. There is slight
difference between the mass of helium formed and the mass of four protons which are fused together.
According to Einstein, energy and mass are interconvertible. Energy E = mc2 where c is the velocity of
light. The difference in mass gets converted into energy.
Birth and Evolution of star. The raw material for formation of a star is mainly H2 gas and some helium
gas. The life cycle of star begins with gathering of H2 gas and helium gas present in galaxies to form
dense clouds of these gases. The stars are then formed by the gravitational collapse of these highly dense
clouds of gases in the galaxy. The first step in the formation of star from gases in the protostar.
Protostar. It is a highly condensed cloud of gases, mainly hydrogen and some helium, formed by the
gravitational contraction of gases present in the galaxy. It looks like a huge, dark ball of gas. The
formation of protostar is only a stage in the formation of complete star. A protostar does not emit light.
Formation of star from protostar. The protostar is a highly dense gaseous mass which continuous to
contract further (shrink further) due to tremendous gravitational force. As the protostar begins to
contract further, the hydrogen atoms present in gas cloud collide with one another more frequently.
Core
Outer shell
Or envelope
(a) A huge cloud of
Contracting hydrogen
gas
(b) A protostar.
(c) A star is formed,
(Formed by the
(Here, hydrogen is
shrinking of huge
converted into helium
cloud of hydrogen
through nuclear fusion)
gas)
Fig. 17.8: Diagrams to explain the formation of a star.
Collisions of hydrogen atoms raise the temperature of protostar from – 173°C to 107°C. At this high
temperature, nuclear fusion of hydrogen stars and high amount of heat and light is emitted.
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4 H  H + huge amount of energy
This further raises the temperature and pressure inside. The protostar now begins to glow and becomes a
star.
The increased pressure from within the star the gaseous matter from collapsing further. The star is now
in delicate equilibrium under two opposing forces – the gravitational attraction trying to compress and
ignite the fusion reaction, and the internal pressure generate by the energy released by fusion. The
balance can continue for thousands of millions of years, the temperature in the interior of the star being
just right to sustain the fusion reaction, and the rate of this reaction is just right for balancing the
pressure of compression. All the while the fusion reaction continues to liberate energy.
Final Stages of a Star’s Life (Red-giant phase). As the fusion continues in the interior of the star,
more and more hydrogen is converted into helium. After some time, the matter in its core will have
mainly helium, and the fusion reactions will stop. The pressure inside the core will then drop and the star
begins to contract again under its own gravity. However, in the outershell, hydrogen will continue to
fuse and liberate energy. The shell would, therefore begin to expand, increasing its surface area and
reducing the intensity of radiant energy. At this stage, the star enters Red-Giant Phase. It will begin to
change color and appear red. Our sun, when reaches this stage will engulf the inner planets Mercury,
Venus and may be Earth also.
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4
2
Corc
Core shrinks
Outer shell expands
Outer shell
or
Envelope
Normal Star
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Red-giant star
Fig. 17.9: Diagram to show the transition from normal star to red-giants star.
In this transition, the core shrinks while the envelope expands.
White dwarf star. One a star reaches the red-giant phase; its further depends on its initial mass. A star
with a mass similar to sun would loose its expanding shell. The core left behind would gradually
condense into and externally ball of matter. The resulting high temperatures in its interior would then,
begin to convert helium into higher elements like carbon in the same way as hydrogen was fused into
helium. The energy liberated by the fusion of helium would make this small core glow as white dwarf
star as long as the helium lasts before fading into dense lump. Matter inside the white dwarf is highly
compressed. One such white dwarf has been observed near the star SIRIUS. In a typical white dwarf
star 10,000 kg are packed in 10–6 m3.
Core
Outer shell is lost;
Core shrinks
Outer shell
Or
Envelope
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Red-giant star
(Having mass similar to the sun)
White
dwarf star
Formation of Supernova Star. If the star is much more massive than the sun, its end could be quite
spectacular. The core of helium formed during the red-giant phase would continue to contract, building
up higher and higher temperatures. As this contraction continues the energy liberated causes the outer
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envelope to explode with a brilliant flash. The explosion of the envelope would be so great that it could
release in one second, the same amount of energy that the sum radiated in about a hundred years. It
would light up the sky for many days. Such an exploding star is called Supernova.
Neutron star. The stars which are composed of matter mainly in the form of neutrons are called neutron
stars. The neutron star arises from the collapsed core of a supernova. After the supernova explosion, the
outershell of the red giant star explodes and only the helium core survives. The core continues to
contract under the tremendous force of gravitation and ultimately it forms and extremely dense lump of
matter which is called neutron star. It has very high densities.
A spinning neutron star emits radio waves and is called a pulsar.
Core
Outer shell
Or Envelope
Supernova explosion
Outer shell explode;
Core shrinks
Neutron
star
Red giant star
(Having mass much than sun)
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Fig. 17.11 Diagram showing the supernova explosion and formation of neutron star.
Black hole. A hole is an object with such a strong gravitational field that even light cannot escape from
its surface. It may be formed by the indefinite contraction of heavy neutron stars under the action of
their own gravity.
They are invisible. They can be felt only the effect of its gravitational field on its neighboring objects in
the sky. One such black hole is seen in the Cygnus constellation.
Chandrashekhar Limiting Mass or Chandrashekar’s Limit. Like everything else, stars do live, and
die. When all hydrogen in them is used up, Helium starts fusing to form carbon. Its core starts
contracting and density becomes very high. This stage of an inactive star is called white dwarf star. This
result of the mass being only 1.4 times the mass of the sun is called Chandershekar limit. Beyond this
mass of 1.4 times the mass of sun, the star explodes into pieces and ends up as neutron stars or Black
holes.
About Dr. Chandershekar. Born on 19th of October 1910, a Physics graduate from the Presidency
College, Madras, he got his first paper published in “Compton Scattering and the new Statistics” at the
age of just 18. He got his PhD from Cambridge University, England in 1933.
Changing Night Sky. As Sun sets, starts rise up in the sky (visibly). The stars can be seen to rise (reach
a designated observing position) 4 minutes earlier than the previous day. They appear to revolve with a
period of 24 hours round the earth. They rise 1 degree per day. In a month they rise 30° higher. The
other stars also change their relative positions. So every month the star map in the sky varies with
season.
Summer Solstice. When the sun is at the greatest angular displacement on Northern side, it is called
summer solstice. It occurs on June 21st and the begins to move towards south. It is called as
Dakshinayan.
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Winter Solstice. When the sun is at the greatest angular displacement on Southern side, it is called
winter solstice. It occurs on 21st December and the sun begins to move towards north. It is called as
Uttaranyan.
Equinox. When the sun appears to cross the celestial equator, it is called euinox. When it crosses south
to north, it is called vernal euinox and occurs on March 21st. At the sun crosses north to south, it is called
autumnal equinox. It occurs on September 23rd.
The Solar System. It consists of the sun, the nine planets and their satellites (or moons) and thousands
of other smaller heavenly bodies such as asteroids, comets and meteors. The sun is at the center of the
solar system and all these bodies are revolving around it. It holds them with a gravitational pull. In other
words, the motion of all the members of solar system is governed by the gravitational force of the sun.
The sun accounts for almost 99.9% of the matter of the whole system.
Venus
Mars
Saturn
Neptune
Sun
Mercury
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Earth
Jupiter
Uranus
Pluto
Terrestrial Planets. The planets, nearest to the sun, called Mercury, Venus, Earth and Mars are called
the terrestrial planets. They are similar in structure to the Earth.
Common features of terrestrial planets:
(i) A thin rocky crust-outer layer.
(ii) A mantle rich in iron and magnesium.
(iii) A core of molten metals.
(iv) Very few moons and
(v) Very thin atmospheres.
Jovian Planets. The planets outside the orbit of Mars are much further than any other planets. The
temperature on those planets is very low. Their atmosphere contains gases like CO2, methane and
ammonia. This makes no possibility for life existing on them. They have rings around them and have
large number of moons.
Planets. They are solid heavily bodies which revolve round the sun in closed elliptical paths. They are
made of rock and metal. They have no light of its own. They shine because it reflects light of the sun.
The planets are very small as compared to sun. There are 9 major including Earth.
Mercury (Budha). It is smallest planet. It is nearest to the sun. It can be seen with the naked eye. It is
very because it is close to the sun. Life is not possible on it. It is fairly bright planet which can be seen in
the east just before sunrise or in west after the sunset. It takes 88 days for one revolution around sun.
Venus (Shukra). It is the brightest object in the night sky except the moon. It has high level of CO2. It is
visible in the early morning in the eastern sky or in the early in the western sky. It appears bright
because it reflects 75% of the light which it receives from the sun. It is 108 × 106 km away from the sun.
its time of revolution around sun is 243 days. It has no moon (satellite). It has/protective blanket to
prevent harmful radiations.
Earth (Prithvi). It is only planet in solar system which is surrounded by oxygen, the gas we need in
order in live. It is only planet where large quantity of water is available. The earth’s atmosphere contains
N2, O2, CO2 and water vapour. The two planets which lie between sun and the earth are Venus and
mercury. The earth has one moon. It is only planet where life exists.
Jupiter (Brihspati). It is the biggest planet of the solar system. It is 778 × 106 km from sun. It takes
11.75 years to complete one revolution around sun. It has 12 moons. It can be seen with naked eye. It
consists of methane, hydrogen and carbon dioxide.
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Saturn (Shani). It is second biggest planet. It is the only planet with a system of rings round it. It is
1427 × 106 km from the sun. It has 10 moons. It takes 29½ years to take one revolution around sun. It
can be seen with naked eye. It contains H2, CO2 and methane.
Uranus (Indra). It is the third largest planet of the solar system. It rotates on its axis from east to west
whereas all other planets revolve from west to east. It has 5 moons. It takes 84 years to complete one
revolution around sun. It is 15 times heavier than earth. It also consists of hydrogen, methane and CO2.
Neptune (Varun). It is the second farthest away form the sun. It is 4504 × 106 km from the sun. It
completes one revolution around sun in 165 days years. It has 2 moons. It cannot be seen with naked
eye.
Pluto (Yama). It is farthest away from the sun as well as earth. It is 5900 × 106 km. It takes 248 years to
complete one revolution around sun. It has no moon. It cannot be seen with naked eye.
Mars (Mangal). It is 228 × 106 km away from sun. It is a cold planet. It takes 687 days to complete one
revolution around sun. It has two moons. Life cannot exist on it due to lack of oxygen and water. Mars
must have earlier a moderate climate and enough surface water. But being a smaller planet, with a
smaller gravitational field, it could not hold on to its CO2. The solar energy which is trapped by the gas
could, therefore no longer be retained.
Differences between Star and Planet
Star
1. A star has its own light.
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Planet
1. A planet does not have its own light. It reflects
that of sun.
2. Stars twinkle at night, which are light 2. They do not twinkle at all.
increases and decreases continuously.
3. Stars and countless.
3. There are only 9 major planets.
4. Stars are very big in size. They appear 4. Planets are very small in size as compared to
small because they are very far off.
stars.
5. Stars do not change their position in sky.
5. Planets change their positions day by day.
6. Stars appear to be moving from east to 6. Planets move around sun from west to east.
west.
7. A star is a huge mass of extremely hot 7. It is made up of rocks and metals and the
gases and its temperature is very high.
temperature depends upon the distance from the sun.
Satellites (Moon). A satellite is a solid heavenly body that revolves round a planet the moon revolves
round the earth, so moo is a satellite of the earth. Five other planets also have their moons. The satellites
have no light of their own. They shine because they reflect the light of the sun.
Moon. The moon is a natural satellite of the earth. It revolves around the earth and gravitational
attraction holds the moon in its orbit. Moon has no air or water. On the moon, days are extremely hot
and nights are very cold. It is near to earth; therefore, it seems bigger than stars.
Asteroids. They are very small planets of rock and metal which revolve around sun mainly between
mars and Jupiter. They are a belt of debris which failed to assemble into planet keeps on revolving
around sun.
Comets. A comet is a collection of gas and dust which appears a bright ball of light in the sky with a
long growing tail which always points away from sun. They revolve around sun like planets, e.g.
Halley’s Comet was last seen in 1986 after 76 years. It is visible only when it approaches sun. Comets
do not last for ever. Each time a comet passes the sun, it loses some gas and ultimately only the dust
particles are left in space. When these particles enter into the earth’s atmosphere, they burn up due to
heat produced by air resistance and produce a shower of meteors or shooting stars.
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Fig. 17.13: A comet in the sky.
Meteors. They are the heavenly bodies from sky which, we see as bright streak of light that flashes for a
moment across the sky. They are also called shooting stars.
Some of them are the dust particles left behind by comets and others are piece of asteroids. Most of them
are smaller than a grain of sand and burn up completely on entering the earth atmosphere but some are
big and do not burn up completely.
Fig. 17.14: A meteor (shooting star) in the night sky.
Meteorite. A meteor which does not burn completely on entering the earth’s atmosphere and lands on
earth is known as meteorite. Meteorites are a sort of stones from the sky.
Differences between Star and Shooting Star.
Star
Shooting Star
1. A star is made up of gases like H2.
1. A shooting star is made up of rock and metal.
2. A star has light of its own.
2. A shooting star has no light of its own.
3. A star does burn due to friction
3. A shooting star burns due to heat produced by
friction on entering atmosphere.
4. A star has very big size.
4. Shooting star is very small.
Asteroid Collide with earth. There is less possibility for an asteroid to collide with the earth. They can
cause large number of craters on the surface. They bring damage to life and property on the earth. The
craters are filled by natural processes like erosion, wind and rain. Only a few craters survived. Lonar
Lake in Maharashtra is one such crater.
Comets as timekeepers. Comets having elliptical orbits are very regular. So we can fix time with their
motion. Since the material content of comets can be used to analyse the life of the celestial bodies in
solar system, one can get an idea regarding the age of the solar system.
SETI. Short form of Search for Extra-Terrestrial Intelligence is the project in which mankind is looking
for the evidence of life of the planetary systems of remote stars.
Formation of sun. The sun was formed about 5000 million years ago from the dense clouds of mainly
hydrogen gas, some helium and dust. The dense cover over and cold cloud of H2 gas shrank under its
molecules in the protostar raised its temperature greatly which started the nuclear fusion reactions. The
nuclear fusion reactions, in which hydrogen was converted into helium, produced a tremendous amount
of energy duo to which the protostar began emitting heat and light and became the sun (which is a star).
The sun would become a red-giant star and die out as white dwarf star after 5000 million years.
Formation of planet. When the sun was formed about 5000 million years ago, the left over gases (mainly
hydrogen and some helium) formed a disc shaped cloud around the sun. These left over gases were very
cold and condensed to form small chunks of matter called planetesimals. These planetesimals started
rearranging themselves by constant collisions among themselves, breaking up and then reassembling to
form various planets.
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Age of solar system. The age of solar system (including earth has been estimated to be about 5000
million years by radiometric dating.
Age of earth. The earth contains various types of rocks. Some of these rocks contain a radioactive
substance called uranium which is unstable and gradually decomposes to form a stable element lead.
The rate at which the atoms of radioactive uranium decay, to form, non-radioactive lead remains
constant (has been determined by experiments). It helps in determining age of earth by using half-life of
uranium which is equal to 4.5 × 109 years.
Age of meteorites. The meteorites falling on the earth contain uranium rocks having radioactive atoms
or uranium and some radioactive atoms of lead. If we know the of uranium of lead we can determine the
age of meteorites. This method is called radioactive dating.
Formation of earth. The earth began as a cold aggregate of planetesimals, Compounds of silicon, iron
and magnesium and traces of other elements were found. As more and more planetesimals collided with
the earth and struck to it, their kinetic energy was converted into heat. Radioactive disintegration of the
atoms of U, Th, K and compression of earth, also heated the planet and eventually melted it some 800
million years after its formation. The earth began to reorganize itself under the influence of gravity. As
the temperature of earth increased, iron melted which formed large drops and began to fall to the center
of the earth displacing lighter elements of the surface.
Differentiation. The organization of earth into different layers is called differentiation. It was divided
into three major layers.
(a) Crust. The outermost layer of earth is called crust. It is made up of lighter rocks rich is silica and Al.
3/4th of earth is covered with water. Over the earth’s crust there is a layer of atmosphere.
Light
rocks
6350 km
Crust
Mantle
Dense
rocks
Outer core
Inner core
Molten
rocks
Earth
Solid iron
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Fig. 17.15: The inner structures of earth.
(b) Mantle. The central region between the crust of the earth and core of earths is called mantle. It
consists of rocks mainly made up of largely iron silicate and magnesium silicate. The pressure inside the
mantle increases with depth. Under extreme pressure and temperature, some of rocks near the bottom of
the mantle tend to flow. The density of mantle increases as we go downwards.
(c) Core. The innermost part of earth is called core. It consists of inner solid sphere surrounded by an
outer fluid shell. The temperature at the center of earth is around 4000°C and the pressure is about 3.7
million times the atmospheric pressure. It is because of high pressure in the inner core that iron can
remain in solid form despite the high temperature. However in outer core where the pressure is lower,
iron becomes molten.
Earth as a special planet.
(a) It has building blocks like carbon, hydrogen, nitrogen and oxygen from which more complicated
molecules can be synthesized.
(b) The temperature is such as to permit life sustaining chemical reactions.
(c) A liquid medium like water to transport nutrients.
(d) A protective blanket around the earth is to prevent harmful radiations from entering the atmosphere.
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Study of earthquake. Earthquake is caused by fracturing and slipping of rocks inside the earth. When
earthquakes occur, they shake the whole body of the earth and hence produce waves and vibrations. The
study of earthquake tells us that the core of the earth is mainly made up of a liquid (molten iron). The
scale used to measure of earthquake is Richter scale. The study of earthquake is called seismology.
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Earthquakes. The convection current in molten magma cause the plates of the lithosphere to glide,
scrape and push each other, sometimes. When the rock is sufficiently slippery at the joint, they interlock
each and put tremendous amount of pressure. This sends shock waves in all the directions and is felt as
earthquake.
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Epicenter. The center from which the earthquake waves originate is called seismic focus and the point
of the earth’s surface vertically above the focus is called epicenter. The intensity of earthquake is
maximum at epicenter and decreases with distances from epicenter. Seismograph records the intensity
and time of occurrence of earthquake.
68.
Consequence of earthquakes. (i) Strong earthquakes can cause damage to life and property. They are
less frequent. (ii) Cracks may appear on earth’s surface over long distance. (iii) River courses may be
altered leading to sudden floods. (iv) Roads, railway lines and buildings may be damaged. (v) In cities,
water pipelines and gas pipelines may get disrupted.
69.
Intensity of earthquake. When earthquake occurs, tremendous amount of energy is released which
sends shock waves all around. The intensity of earthquake is indicated by the amount of energy released
when the plates of lithosphere give way (break) due to pressure from within the earth. The intensity is
earthquake which do not cause may damage to life and property. Earthquake, which is measured 8 or
more on Richter scale can destroy entire cities and villages causing a great loss to life and property.
70.
Composition of atmosphere. The majority of earth’s cover of gases which we call the atmosphere
extends up to about 40 km. Even above this height from the surface, gases are distributed very thinly. 99
percent of the air resides in first 40 km. Traces of air have been observed even above 100 km.
Atmosphere contains mainly N2 and O2 along with small amounts of CO2 water, vapour, the rare gases
argon, neon, krypton and xenon and fine dust particles.
71.
Ozone. Oxygen is converted into ozone in upper atmosphere by action of U. V. light. Ozone is a
molecule with three atoms of oxygen (O3). Ozone blanket is thickest at about 23 km. It absorbs U. V.
radiations from the sun and protests us from U. V. light.
72.
The Big-Bang theory. According to this theory, all the matter in the universe was originally
concentrated in one vast lump called primeval atom which was 100 million light years wide. About 15
billion years ago, this superdense and extremely hot primeval atom (which was a concentrate of neutrons
and protons) exploded with a big-bang, galaxies of stars and other heavenly bodies. It suggests that
universe has definite age and definite size.
73.
The Beginning of the Universe. Galaxies are the building blocks of the universe. All the galaxies are
traveling away from one another at a great speed. The speed with which the galaxies run away from one
another is directly proportional to the distance between them. Since the galaxies are racing away from
one another at present, so many astronomers believe that they must have originally started from a single
point is space. It is concluded that the universe began in a big bang (big explosion).
74.
Doppler Effect. The apparent change in frequency of sound or light due to relative motion between the
observer and the source of energy is called Doppler Effect.
As the source moves towards the stationary observer, the frequency increases (wavelength decreases)
and when the source moves away the frequency decreases (wavelength increases).
Application. When Doppler effect is applied to light waves coming from various stars in the galaxies, it
tell us that the various galaxies are receding from us (moving away from us) or coming towards us with
greater and greater speeds. It has been concluded that all galaxies move away from one another
continuously. If star is moving towards the earth, then the frequency of light emitted by it will increase
gradually and shifts towards the violet end of visible spectrum, it is called violet shift. On the other
hand, if the star is moving away from away from earth, the frequency of light emitted will decrease and
shift towards red end of spectrum. It is called red shift.
75.
Space Exploration. The collection of information about the various objects in outer space is called
space exploration.
Graphics By: - Roshan Dhawan
- 11 Written By:- R K. Badhan
76.
77.
THE UNIVERSE
Satellite. A satellite is a celestial object revolves around a planet in a circular path or elliptical path.
They are two types:
(a) Natural Satellite. The satellites which occur in nature are called natural satellite, e.g. moon is natural
satellite or earth.
(b) Man-made Satellite. These satellites are man-made and they revolve around the earth. They are also
called artificial satellite, e.g. INSAT-IB.
Orbit. The closed path of a satellite around the earth is called its orbit. It may be circular or elliptical is
shape. The various characteristics which define the orbit of a satellite around the earth are.
(i) Apogee. It is the farthest point ‘A’ from the earth on the orbit of a satellite.
(ii) Perigee. It is the nearest point ‘B’ from the earth of the orbit of the satellite.
(iii) Inclination. It is the angle made by the orbit of satellite with the equator of the earth. It is shown by
angle C in the Fig. 17.16.
A
Apogee
Satellite
Inclination
equator
Earth
C
B
78.
Perigee
History of Space Exploration.
(i) Sputnik I. (Meaning fellow traveler). It was launched by USSR on 4th October 194. It was the first
artificial satellite in space. In satellite weighed 84 kg. It had an orbit with apogee of 941 km and perigee
of 277 km. It was launched to carry out studies as a part of International Geographical Year. The USA
sent Explorer after few months later. It weighed only few kg.
(ii) Sputnik II. It was launched on 3rd Nov. 1957 by USSR. It was the first satellite which carried a
living dog ‘Lalika’ into space. The weight of satellite was 500 kg. The blood pressure, temperature and
heart beat of Lalika were maintained from the earth for eight days. The data provided vital information
and paved the way for putting the first man into space.
(iii) Score. It was first communication satellite put into space on 18th Dec. 1958.
(iv) Luna 3. It was the first space probe which sent photographs of the far side of moon which is not
visible from earth. It was sent on 4th Oct. 1959.
(v) Vostok I. Yuri Gagarin of USSR was the first man in space who completed a single orbit around the
earth on 12th April 1961. The USA followed the event on 5 May 1961 when Alan Shepherd becomes
first American to go into space.
(vi) Vostak II. The first woman Valentina Tereshkova of USSR sent into space on 4th Dec. 1963.
(vii) INTELSAT I. It was first communication satellite for commercial use put into space. It was sent
on 16th April 1965.
(viii) Venera 3. The spacecraft sent to another planet ‘Venus’ on 16th November 1965.
(ix) Luna 9. The first successful soft landing of space-probe on the surface of moon on 21st October
1968.
(x) Soyuz 4. On 14th Jan. 1969 first experimental space was established.
(xi) Apollo II. On 16th July 1969 Apollo-II was sent into space with Neil Armstrong of America who
landed on Moon first time on 20th July 1969. Edwin Aldrin was the second to land on moon.
(xii) Mars 2. It was the first landing of space probe on the planet ‘Mars’ on 19th May 1971.
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THE UNIVERSE
(xiii) Pioneer 10. It was the first space probe to explore the asteroid belt and to take photograph of the
planet “Jupiter” from close range on 2nd March 1972.
(xiv) LANDSAT 1. The first satellite dedicated to remote sensing. It was launched on 10th July 1972,
(xv) Apollo Soyuz Test Project. The first international link up of satellite in space on 15th July 1975.
The significant development in area of space science during the eighties was the establishment of
permanent space stations and development of space shuttles which were used to carry astronaut’s
permanent observatory in space and the maiden flight of Voyager II to all planets of the solar system are
other significant developments of the eighties. Another remarkable achievement has been carrying our
repaired satellite was put back on its original orbit.
79.
Space Science in India. India is one of the six nations of the world which has the technical know how
for putting satellite in an orbit around the earth. The objectives of space research programme in India
are:
(i) Rapid development of mass communication and education especially in widely dispersed rural
communities and
(ii) Timely survey and management of the country’s natural resources.
80.
ISRO. (Indian Space Research Organization). It is involved in development of know how to fabricate
the rocket, its propellants, its control and guidance systems and to design and fabricate satellites. The
first Indian rocket RH-75 was launched in 1967 from Thumba Equatorial Rocket launching station
(TERLS) near Thiruvananthapuram on 20 May 1992, ASLV (Augmented Satellite Launch Vehicle) was
launched. The objectives of Indian space progamme are:
(i) Development of expertise in planning, designing and fabricating space satellites for various purposes.
(ii) Development of suitable launch vehicles to place satellite in predetermined orbits around the earth.
81.
Aryabhata. It was the fist Indian satellite launched from Soviet Union. It was purely experimental in
nature. The satellite enabled Indian scientists to develop the skills and facilities for fabricating satellites
and monitoring their performance in the orbit. It also facilitated establishment of ground facilities for
communicating with satellite tracking it and passing commands to it to carry out various tasks. It helped
to conduct some experiments in the field of X-ray, astronomy, solar physics and meteorology (weather
forecasting).
82.
Bhaskra-I. It was second Indian satellite which was launched on 7th June 1979 from Soviet Union. It
was used to develop expertise in collecting data on natural resources through remote sensing techniques.
Groundwater surveys, forestry and geological surveys were conducted through this satellite by
collecting valuable data until March 1981.
83.
Bhaskra-II. It was launched on 20th November 1981, functioned successfully for over two years. It was
similar to Bhaskra-I with some improvements.
84.
IRS-IA. The first Indian Remote Sensing Satellite, IRS-IA, was launched on 17th March 1988 while
IRS-IB was successfully put into orbit on 29 August 1991. Both these satellite were launched from
USSR. The IRS-IB is still operational and is providing valuable data relating to a variety of resources.
85.
APPLE. (Ariane Passenger Pay Load Experiment). It was third type of Indian satellite. It was launched
on 19th June 1981 with the help of the European Space Agency from Kouron launching facilities in
French Gayana (South America). This was the first Indian satellite put in a geostationary orbit.
86.
Geostationary orbit. The orbit of satellite is called geostationary orbit if the position of the satellite
does not change with respect to a first station of the earth.
87.
Geostationary orbit. The satellite whose period of revolution in its orbit is same as the period of
rotation of earth about its axis that is 24 hours.
88.
INSAT (Indian National Satellite). It was first operational satellite on a commercial basis. It was
expected to carry out three independent tasks
(i) Communication (ii) Television an radio broadcasting (iii) meteorological observations. INSAT-IA
was launched on 4th September 1982 which failed in its mission. INSAT-IB was paved the way for
revolutionising communication system in India. The INSAT-IC intended to replace INSAT-IB was a
failure. The INSAT-ID was put into geostationary orbit in June 1990.
The first Indian satellite INSAT-2A was launched in 1992 and was unsuccessful. The first success in the
launching of an indigenously developed Indian satellite was achieved on 18th July 1980. The launch
Graphics By: - Roshan Dhawan
- 13 Written By:- R K. Badhan
89.
90.
91.
THE UNIVERSE
vehicle for carrying the satellite was a four stage rocket SLV-3. It carried a 35 kg satellite named
‘Rohini’ into an orbit with an apogee of 900 kg and perigee of 300 kg. The main objective of this launch
was of test the performance of the fourth stage of the launch vehicle. The fourth satellite was
successfully launched on 17th April 1983.
SROSS (Streched Rohini Satellite) was developed after the Rohini series. The second generation
launch vehicle (ASLV) was also developed simultaneously. The first attempt to launch SROSS-1 by
(ASLV) on 24th March 1987 was a failure. The second attempt to launch SROSS-2 by ASLV on 13th
July 1988 also met with failure. It provided valuable data and information on various aspects of the
ASLV flight o determine the reasons for its failure. The analysis of the data so obtained was utilized to
incorporate many modifications in he design of ASLV. On 10th July 1992 historic event of launching of
an Indian Satellite on an Indian launch vehicle took place. The launch vehicle was a 23 meter tall five
stage solid fuelled rocket ASLV-D3, a modified version of ASLV. It carried with it 106 kg SROSS-C
satellite and placed it into an orbit 450 km above the earth.
PSLV (Polar Satellite Launch Vehicle). It will use a solid propellant in the first and third stage while
in the stage and fourth stages, liqid propellant. GSLV (Geostationary Satellite Launch Vehicle) will also
be used in future.
Application of Space Science.
(i) Satellite Communication. It is done through geostationary satellite. These satellites have devices
which can receives signals from an earth station and transmit them again in different directions. Such a
device is called TRANSPONDER. The signals in the form of electromagnetic waves carrying audio
(sound) or video (picture) messages are transmitted from earth station like TV transmitter, which are
received by satellite by satellite and they sent the signals in all direction which are received by large
number of ground stations located on various regions. The signals received from the satellite are weak,
therefore, the ground stations amplify the signals before transmitting them again. It is actually these
signals which are received by TV sets located far away from programme transmitting stations. Similar
mechanism is used fro sending messages through telecommunications like telephone, telex (i.e. printed
message) and FAX (i.e. facsimile of printed matter or pictures). It is used for international
communication; often two or more satellite is linked together.
(ii) Weather Monitering. Satellites are used in collecting information about carious factors of
atmosphere which governs the weather and climating conditions, everybody an aerial photograph of the
country is shown on T.V. The data collected by INSAT satellite has enabled our scientists to make short
term and long term prediction about weather. It is now possible to get prior information about an
emergency cyclone or floods or possible rain or drought conditions.
(iii) Remote sensing. It refers to collections of information about an object without physical contact
with that object and using Imaging techniques. The orbits of the satellites dedicated to remote sensing
are such that the satellite passes over particular latitude at approximately at the same local time. It means
that the position of the sun with respect to a point on earth remains approximately the same as the
satellite passes over it. Such orbits are called sun-synchronous orbit. It enables remote sensing satellite
to take photographs of a particular region with nearly the same illumination every time it passes through
that region.
The data receive by Indian remote sensing IRS-IA and IB has been used for (i) forestry (ii) preparing
wasteland maps (iii) ground water surveys (iv) agriculture (v) drought assessment (vi) estimation of crop
yields and detection of crop diseases and (vii) detection of potential fishing zones.
It has made possible repetitive surveys of remote areas in very short time even if the areas are
inaccessible.
(iv) Collection of Information about planets and outer space. The leading on moon by man has
provided an opportunity to collect information about surface of moon, its structure and composition.
Voyager spacecrafts launched by the USA have transmitted photographs of all planets from close range.
Voyager spacecrafts have discovered new rings of moons Saturn. Voyager’s camera has detected four
previously unknown of Neptune, in addition to two satellites known earlier. It has also discovered two
rings around Neptune.
Graphics By: - Roshan Dhawan
- 14 -
Written By:- R K. Badhan
92.
93.
94.
95.
96.
THE UNIVERSE
The application of space technology are expanding at such a pace that the present era can be called ‘the
space age’.
Launch of an Artificial Satellite. Bodies thrown up in space returns back to the surface of earth, due t
gravi tational pull of earth. Unless it is given sufficient energy to overcome this pull, it cannot escape the
gravitational pull of earth; artificial satellites are powered by rockets of multistage fuel combustion.
After acquiring sufficient velocity, they are directed towards an orbit-predetermined. The minimum
velocity required to escape from the gravitational pull of the earth is called escape velocity. The velocity
with which these satellites are placed in an orbit is called orbital velocity. The minimum speed for an
orbit, close to the surface of each is 8 km/second.
Characteristics of furls used in Rockets.
1. Should burn rapidly.
2. Release large energy without unburnt particles or ash.
3. Bring high pressure gas at large volume.
4. Should not explode violently and should be easily controlled in flow and combustion.
Liquid fuels. Mixture of liquid hydrogen and oxygen, or kerosene with liquid oxygen. They are carried
in separate chambers and allowed to mix in the combustion chamber. It is risky to store them due to
leakage problem.
Solid fuels. Mixture of aluminium powder and ammonium nitrate or ammonium percholae.
Orbital velocity. Consider a satellite of mass going around the earth Mass ‘m’. If the orbit is at a height
GMm
‘h’ above the surface of earth, the force of gravitation =
2
R  h
Where R is the radius of earth of mass M. The centripetal force required is given by this gravitational
force. If v0 is the orbital velocity then,
Vo
mv02
GMm

 R + h   R + h 2
R
Earth
Satellite
GM
M
v0 
m
h
R+h
If r = (R + h) is the distance of the satellite from the center of earth.
GM
Then, v0 
r
(R + h)
Relation between time period and height of satellite. We know that, velocity =
distance travelled
time taken
2r
where T is the time period of
T
revolution of the satellite. Since r = R + h (i.e.) h = r – R, the orbital velocity depends on the height of
the satellite.
Kepler’s Law. According to this law of Kepler, the square of the time period T of a satellite to move
around the earth is directly proportional to the cube of the distance of the satellite from the center of the
earth r.
(i.e) T²  r³
Proof of Kepler’s law. We know that,
 In a orbit of radius r = (R + h), the velocity of the satellite is, v0 
97.
98.
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Written By:- R K. Badhan
THE UNIVERSE
mv
GMm
2r
 2 and v0 
r
r
T
GM 2r

v0 

r
T
squaring either side, we have,
2
0
GM 42 r 2

r
T2
4 3 r 3

T2 
 i.e. T 2 r 3
GM
1 MARK QUESTIONS
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
Which planet of the solar system is the hottest?
Name the planet nearer to and farthest from the sun.
Besides Earth, which other planet has a protective blanket to prevent harmful radioations?
Name the planet which could not hold on to its carbondioxide due to its smaller gravitational field.
Write one point of difference between a star and a neutron star.
Draw the shape of the constellation “Great Bear” showing the position of stars.
Draw the shape of the constellation ‘Orion’ showing the position of stars.
How is a protostar formed?
Name any two constellations that are visible during winter in the northern hemisphere.
On what basis is predicted whether a star would end up as a white dwarf or as a supernova?
Between which two planets do the asteroid lie?
What is a pulsar?
What is neutron star?
Which planet takes maximum time in one revolution round the sun?
Who proposed the Big-Bang theory about the origin of universe?
Who discovered that all galaxies are moving away from each other?
Name the fuel of (i) a white dwarf star and (ii) the sun.
During which season of the year are the constellations of Orion and Scorpio visible?
Name the gases that constitute a protostar.
Name any one celestial object that emits waves.
What are planetesimals?
Name two planets, which are between the sun and the earth.
What are asteroids?
A constellation having 7 prominent stars is visible during the winter. Name the constellation.
A group of stars visible in winter season looks like a cluster of twinkling stars. Name such group of
stars.
A star is now 20 times heavier than the sun. What will it be in future-a white dwarf or a
supernova?
Which one of the following will ultimately turn into a neutron star:
White dwarf or supernova?
Which two planets have asteroids between them?
Write any one difference between a protostar and the sun.
Mention one point of difference between a red giant star and a white dwarf star.
Write one point of difference between a neutron star and the sun.
Name the fuel of a star when it glows in its red giant phase.
Name the two forces acting in star which prevent it form collapsing.
State the factor which decides the future of a star after the red giant phase.
Name the planet which us farthest from the sun than Neptune.
Graphics By: - Roshan Dhawan
- 16 -
Written By:- R K. Badhan
36.
37.
38.
39.
40.
THE UNIVERSE
Give one resemblance between the structure of atom and the solar system.
Give the evidence in favour of big-bang theory.
Write the name of dense contracting gaseous mass of helium and hydrogen as found in the life of a
star.
Notice the pattern of star shown in the figure below. Identify the constellation corresponding to it.
Notice the pattern of stars shown in the diagram below. Identify the constellation corresponding to
it.
1
2
6
5
4
7
41.
42.
43.
44.
45.
46.
3
Name the scientist who proposed the big-bang theory.
What are the differences between fuel of sun and white dwarf?
Which of the following are constellations?
Pleides, Sirius, Pole Star, Great bear.
Write the names of any two constellations.
In which of the following, the source of energy is fusion of helium nuclei:
A protostar, a red giant star, a white dwarf, the sun
Name the star which is nearest to the earth.
2 MARKS QUESTIONS
1.
2.
3.
4.
5.
What are meteorites? How are they dated?
What are constellations? At what time of the year is Scorpio constellation seen?
How is the formation of stars different from that of planets?
At what time of h year is orion constellation seen? Draw the diagram showing the position of stars.
What is a constellation? Draw a diagram to show the relative positions of stars in the Constellation
orion.
6.
Two constellations are seen in the sky having seven prominent stars in each. Name the one which
appears during winter. Draw its diagram showing the position of stars.
7.
Explain why (i) Venus and (ii) Mars cannot retain water on their surface.
8.
What is meant by a constellation? Draw the shape of Ursa Major showing the position of stars in
it.
9.
State two observations made by Edwin Hubble which led to the formulation of Big-Bang theory.
10.
What is a galaxy? Draw diagrams to show the shape of Milky Way, when seen from (i) front and
(ii) side.
Graphics By: - Roshan Dhawan
- 17 Written By:- R K. Badhan
THE UNIVERSE
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
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31.
32.
33.
34.
35.
36.
37.
38.
Give two differences between a star and a shooting star.
Describe the sequence of events occurring in the final stages of star’s life when the initial mass of
the star is made more than that of the sun.
What is supernova? When does a supernova form?
How were the planets formed? Name the group of objects left out from the planet formation.
Between which two planets do these objects lie?
An astronomer located a celestial object by detecting radio waves emitted by it. He found that this
object had very small and its mass density was very high. Name the category of celestial objects to
which it belongs. Describes hoe it might have been formed.
A star ends its life as a neutron star. Can a star having double the mass of the star and its life as a
white dwarf? Give reasons.
How does the Milky Way galaxy appear when it is viewed from the front an from the side? Show
these views by appropriate diagrams.
Draw the shapes of any two constellations and mention their names.
Name the season in which scorpio is visible on the earth. Draw a diagram to show the position of
stars in Scropio.
List two differences between a planet and a star.
List four conditions for life to exist on planets.
Astronomers believe that planet Mars must have had earlier a moderate climate and enough
surface water. In spite of this, why life could not originate and flourish on it. Give two reasons.
List four physical characteristics according to which stars can be classified.
Give two differences between a galaxy and a constellation.
A star of mass 100 times that of the sun has entered its red giant phase. Explain the changes it
would undergo during the next two phases of its life.
Galaxies A and B moving away from each other with a speed of 2 × 108 cm/s white galaxies C and
D are moving away from each other with a speed of 2.5 × 108 cm/s. In which pair, the two galaxies
would be separated by a longer distance. Give reason.
The distance between the two members galaxies be moving away from each other at galaxies A
and B. In which pair will the two member galaxies be moving away from each other at a great
speed? Give reason.
The distance between the galaxies A and B is x light years while that between the galaxies C and D
is 1.5 x light years. In which pair will the two galaxies be moving away from each other at a higher
speed? Give reason.
How does the big-bang theory explain the formation of heavenly bodies in the universe?
Define a light year. What is a parsec?
Which stage comes earlier in the life of a star protostar or neutron star? State the names of the
gases and the temperature of the cloud which form a star.
Distinguish between a star and a planet.
How are meteorites dated?
Name the characteristics involved in the final stages of the life of a star.
What is the evidence for the hypothesis that the universe began with a big-bang?
What is a comet? Name the periodic comet that appeared in 1986 after a period of 76 years.
What is the shape and size of the Milky Way? Why is the Milky Way not uniformly bright
through out?
3 MARKS QUESTIONS
1.
2.
3.
State what is meant by “Expanding Universe”. Who discovered that the universe is expanding?
What was the basis of the discovery?
When does a supernova occur? Describe what happens during this period.
Describe the final stages in the life cycle of the star of the size of the sun.
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Written By:- R K. Badhan
4.
5.
6.
7.
8.
9.
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18.
19.
20.
THE UNIVERSE
Why is there no life on (a) Venus (b) Mars and (c) Mercury? Write two reasons for each in
support of your answer.
What happens after a star has reached red giant phase?
Describe sequentially the different stages in the process of evolution of star starting from
accumulation of galactic cloud to its birth.
The mass of a star is 10 times that of sun. Describe last two stages in its life cycle.
State the evidence that led to the hypothesis that the universe is expanding. Name the scientist who
made these observations and what were his conclusions about the origin of the universe?
The mass of star ‘A’ are one tenth of that of star ‘B’. If the mass of A is nearly equal to that of the
sun, which one of the two stars will end up as supernova? What would happen to the other star at
the end of red giant phase?
Describe briefly the formation of a star a protostar.
Write two points of differences between a galaxy and a constellation. Name a constellation which
resembles a large ladle, a cluster of twinkling gems.
Write any four differences between star and planets. Name the planet (i) farthest from the earth
(ii) nearest to the earth.
What is Big-Bang theory? Who proposed it? How does this theory explain the formation of
heavenly bodies in the universe?
The mass of a star is 25 times greater than the sun. Explain the different stages that would take
place after its red giant phase is over?
Who discovered that the universe is expanding? What was the basis of this discovery? State the
law connected with it?
What is red giant phase in the life of a star? If the mass of star is many times larger than that of
the sun, explain what would happen to it after its red giant phase it over.
What is the red giant phase of a star? Describe how it is important in the life of a star. When will
our sun enter red giant phase?
Mention four conditions which need to exist on a planet for life to originate and flowish. Which
one of these conditions is not present on the planet Venus?
State the differences between a star and a planet.
What are meteors? How do they become visible? How do they differ from a meteorite?
SELF EVALUATION TEST
Graphics By: - Roshan Dhawan
- 19 -
Written By:- R K. Badhan
THE UNIVERSE
Time Allowed: 1 Hour
Max. Marks: 25
1.
Name a celestial object that can be used as a time keeper?
2.
Write the full form of (i) INSAT and (ii) GSLV.
3.
What is the significance of a Pole Star?
4.
What are terrestrial and jovian planets? Give example for each.
5.
How do stars differ from planets?
6.
What are seismic waves? How do they convey information to us?
7.
What is Dr. Chandrasekhar’s limit? How does it suggest the path of the life of a star?
8.
Does our night sky remain the same always? Name two constellations seen in winter season and
show their pattern.
9.
Name the types of fuels used for launch vehicles. Why do we have to use large fuel and acquire
large energy to launch a satellite? What is the minimum velocity to be provided from the surface
of earth?
10.
What is big-bang theory? Who proposed it? How does it support the view of expanding Universe?
11.
(i) What is Orbital velocity? Derive an expression for the same.
(ii) For a satellite to be in geostationary orbit, derive the height of the orbit.
Graphics By: - Roshan Dhawan
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Written By:- R K. Badhan