NCERT Textbook: The Earth in the Solar System | Social Studies (SST) Class 6 PDF Download

 Page 1


THE EARTH IN THE SOLAR SYSTEM
How wonderful it is to watch the sky after sunset! One
would first notice one or two bright dots shining in
the sky. Soon you would see the number increasing.
You cannot count them any more. The whole sky is
filled with tiny shining objects – some are bright, others
dim. It seems as if the sky is studded with diamonds.
They all appear to be twinkling. But if you look at
them carefully you will notice that some of them do
not twinkle as others do. They simply glow without
any flicker just as the moon shines.
Along with these bright objects, you may also see
the moon on most of the days. It may, however, appear
at different times, in different shapes and at different
positions. You can see the full moon only once in about
a month’s time. It is Full moon night or Poornima. A
fortnight later, you cannot see it at all. It is a New
moon night or Amavasya. On this day, you can watch
the night sky best, provided it is a clear night.
Do you wonder why can’t we see the moon and all
those bright tiny objects during day time? It is because
the very bright light of the sun does not allow us to see
all these bright objects of the night sky.
The sun, the moon and all those objects shining in
the night sky are called celestial bodies.
Some celestial bodies  are very big and hot. They
are made up of gases. They have their own heat and
light, which they emit in large amounts. These celestial
bodies are called stars. The sun is a star.
Countless twinkling stars in the night sky are
similar to the sun. But we do not feel their heat or
light, and they look so tiny because they are very very far
from us.
1
1
Let’s Do
You’ll need : 1 torch,
1 sheet of plain
paper, pencil and a
needle.
Step :
1. Place the torch in the centre
of the paper with its glass
front touching the paper.
2. Now draw a circle around
the torch.
3. Perforate the paper with the
needle within the circled
area.
4. Now place the perforated
circle part of the paper on
the glass front and wrap the
paper around the torch
with a rubber band.
5. Take care that the switch
of the torch is not covered.
6. In a dark room, stand at
some distance facing a
plain wall. Switch off all
other lights. Now flash the
torch light on the wall. You
will see numerous dots of
light on the wall, like stars
shine in the night.
7. Switch on all the lights in
the room. All dots of light
will be almost invisible.
8. You may now compare the
situation with what happens
to the bright objects of the
night sky after the sun rises
in the morning.
Rationalised 2023-24
Page 2


THE EARTH IN THE SOLAR SYSTEM
How wonderful it is to watch the sky after sunset! One
would first notice one or two bright dots shining in
the sky. Soon you would see the number increasing.
You cannot count them any more. The whole sky is
filled with tiny shining objects – some are bright, others
dim. It seems as if the sky is studded with diamonds.
They all appear to be twinkling. But if you look at
them carefully you will notice that some of them do
not twinkle as others do. They simply glow without
any flicker just as the moon shines.
Along with these bright objects, you may also see
the moon on most of the days. It may, however, appear
at different times, in different shapes and at different
positions. You can see the full moon only once in about
a month’s time. It is Full moon night or Poornima. A
fortnight later, you cannot see it at all. It is a New
moon night or Amavasya. On this day, you can watch
the night sky best, provided it is a clear night.
Do you wonder why can’t we see the moon and all
those bright tiny objects during day time? It is because
the very bright light of the sun does not allow us to see
all these bright objects of the night sky.
The sun, the moon and all those objects shining in
the night sky are called celestial bodies.
Some celestial bodies  are very big and hot. They
are made up of gases. They have their own heat and
light, which they emit in large amounts. These celestial
bodies are called stars. The sun is a star.
Countless twinkling stars in the night sky are
similar to the sun. But we do not feel their heat or
light, and they look so tiny because they are very very far
from us.
1
1
Let’s Do
You’ll need : 1 torch,
1 sheet of plain
paper, pencil and a
needle.
Step :
1. Place the torch in the centre
of the paper with its glass
front touching the paper.
2. Now draw a circle around
the torch.
3. Perforate the paper with the
needle within the circled
area.
4. Now place the perforated
circle part of the paper on
the glass front and wrap the
paper around the torch
with a rubber band.
5. Take care that the switch
of the torch is not covered.
6. In a dark room, stand at
some distance facing a
plain wall. Switch off all
other lights. Now flash the
torch light on the wall. You
will see numerous dots of
light on the wall, like stars
shine in the night.
7. Switch on all the lights in
the room. All dots of light
will be almost invisible.
8. You may now compare the
situation with what happens
to the bright objects of the
night sky after the sun rises
in the morning.
Rationalised 2023-24
2
THE EARTH : OUR HABITAT
Figure 1.1 : Saptarishi and the
North Star
You must have noticed that all
objects look smaller when seen from a
distance. How small an aeroplane looks
when it is flying at a great height!
While watching the night sky, you
may notice various patterns formed by
different groups of stars. These are
called constellations. Ursa Major or
Big Bear is one such constellation. One
of the most easily recognisable
constellation is the Saptarishi (Sapta-
seven, rishi-sages). It is a group of seven
stars (Figure 1.1) that forms a part of
Ursa Major Constellation. Ask someone
elder in your family or neighbourhood
to show you more stars, planets and
constellations in the sky.
In ancient times, people used to
determine directions during the night
with the help of stars. The North star
indicates the north direction. It is also
called the Pole Star. It always remains
in the same position in the sky. We can
locate the position of the Pole Star with
the help of the Saptarishi. Look at
Figure 1.1. You will notice that, if an imaginary line is
drawn joining the pointer stars and extended further,
it will point to the Pole Star.
Some celestial bodies do not have their own heat
and light. They are lit by the light of the stars. Such
bodies are called planets. The word ‘planet’ comes from
the Greek word “Planetai” which means ‘wanderers’.
The earth on which we live is a planet. It gets all its
heat and light from the sun, which is our nearest star.
If we look at the earth from a great distance, say the
moon, it will appear to be shining just as the moon.
The moon that we see in the sky is a satellite. It is a
companion of our earth and moves round it. Like our
earth, there are seven other planets that get heat and
light from the sun. Some of them have their moons too.
THE SOLAR SYSTEM
The sun, eight planets, satellites and some other
celestial bodies known as asteroids and meteoroids
Interesting Fact
Jupiter, Saturn and
Uranus have rings
around them. These
are belts of small debris.
These rings may be
seen from the earth
with the help of powerful
telescopes.
Rationalised 2023-24
Page 3


THE EARTH IN THE SOLAR SYSTEM
How wonderful it is to watch the sky after sunset! One
would first notice one or two bright dots shining in
the sky. Soon you would see the number increasing.
You cannot count them any more. The whole sky is
filled with tiny shining objects – some are bright, others
dim. It seems as if the sky is studded with diamonds.
They all appear to be twinkling. But if you look at
them carefully you will notice that some of them do
not twinkle as others do. They simply glow without
any flicker just as the moon shines.
Along with these bright objects, you may also see
the moon on most of the days. It may, however, appear
at different times, in different shapes and at different
positions. You can see the full moon only once in about
a month’s time. It is Full moon night or Poornima. A
fortnight later, you cannot see it at all. It is a New
moon night or Amavasya. On this day, you can watch
the night sky best, provided it is a clear night.
Do you wonder why can’t we see the moon and all
those bright tiny objects during day time? It is because
the very bright light of the sun does not allow us to see
all these bright objects of the night sky.
The sun, the moon and all those objects shining in
the night sky are called celestial bodies.
Some celestial bodies  are very big and hot. They
are made up of gases. They have their own heat and
light, which they emit in large amounts. These celestial
bodies are called stars. The sun is a star.
Countless twinkling stars in the night sky are
similar to the sun. But we do not feel their heat or
light, and they look so tiny because they are very very far
from us.
1
1
Let’s Do
You’ll need : 1 torch,
1 sheet of plain
paper, pencil and a
needle.
Step :
1. Place the torch in the centre
of the paper with its glass
front touching the paper.
2. Now draw a circle around
the torch.
3. Perforate the paper with the
needle within the circled
area.
4. Now place the perforated
circle part of the paper on
the glass front and wrap the
paper around the torch
with a rubber band.
5. Take care that the switch
of the torch is not covered.
6. In a dark room, stand at
some distance facing a
plain wall. Switch off all
other lights. Now flash the
torch light on the wall. You
will see numerous dots of
light on the wall, like stars
shine in the night.
7. Switch on all the lights in
the room. All dots of light
will be almost invisible.
8. You may now compare the
situation with what happens
to the bright objects of the
night sky after the sun rises
in the morning.
Rationalised 2023-24
2
THE EARTH : OUR HABITAT
Figure 1.1 : Saptarishi and the
North Star
You must have noticed that all
objects look smaller when seen from a
distance. How small an aeroplane looks
when it is flying at a great height!
While watching the night sky, you
may notice various patterns formed by
different groups of stars. These are
called constellations. Ursa Major or
Big Bear is one such constellation. One
of the most easily recognisable
constellation is the Saptarishi (Sapta-
seven, rishi-sages). It is a group of seven
stars (Figure 1.1) that forms a part of
Ursa Major Constellation. Ask someone
elder in your family or neighbourhood
to show you more stars, planets and
constellations in the sky.
In ancient times, people used to
determine directions during the night
with the help of stars. The North star
indicates the north direction. It is also
called the Pole Star. It always remains
in the same position in the sky. We can
locate the position of the Pole Star with
the help of the Saptarishi. Look at
Figure 1.1. You will notice that, if an imaginary line is
drawn joining the pointer stars and extended further,
it will point to the Pole Star.
Some celestial bodies do not have their own heat
and light. They are lit by the light of the stars. Such
bodies are called planets. The word ‘planet’ comes from
the Greek word “Planetai” which means ‘wanderers’.
The earth on which we live is a planet. It gets all its
heat and light from the sun, which is our nearest star.
If we look at the earth from a great distance, say the
moon, it will appear to be shining just as the moon.
The moon that we see in the sky is a satellite. It is a
companion of our earth and moves round it. Like our
earth, there are seven other planets that get heat and
light from the sun. Some of them have their moons too.
THE SOLAR SYSTEM
The sun, eight planets, satellites and some other
celestial bodies known as asteroids and meteoroids
Interesting Fact
Jupiter, Saturn and
Uranus have rings
around them. These
are belts of small debris.
These rings may be
seen from the earth
with the help of powerful
telescopes.
Rationalised 2023-24
3
THE EARTH IN THE SOLAR SYSTEM
1. MERCURY - One orbit around sun - 88 days,
One spin on axis - 59 days.
2. VENUS - One orbit around sun - 255 days.
One spin on axis - 243 days
3. EARTH - One orbit around sun - 365 days.
One spin on axis - 1 day
Number of moons - 1
4. MARS - One orbit around sun - 687 days
One spin on axis - 1 day,
number of moons - 02
5. JUPITER - One orbit around sun - 11 years, 11
months about 12 years. One spin on
axis - 9 hours, 56 minutes, number of
moons - about 53
6. SATURN - One orbit around sun - 29 years, 5
months. One spin on axis - 10 hours 40
minutes, number of moons - about 53.
7. URANUS - One orbit around sun - 84 years. One
spin around axis - 17 hours 14 minutes,
number of moons - about 27.
8. NEPTUNE - One orbit around sun - 164 years.
One spin on axis-16 hours 7
minutes, number of moons - 13.
Inner planets - very close to the sun. They are made up
of rocks.
Outer Planets - Very-very far from the sun and are huge planets made up of gases and liquids.
Figure 1.2 : The Solar System Saurce: https://planetarynames.wr.usgs.gov/Page/Planets
Rationalised 2023-24
Page 4


THE EARTH IN THE SOLAR SYSTEM
How wonderful it is to watch the sky after sunset! One
would first notice one or two bright dots shining in
the sky. Soon you would see the number increasing.
You cannot count them any more. The whole sky is
filled with tiny shining objects – some are bright, others
dim. It seems as if the sky is studded with diamonds.
They all appear to be twinkling. But if you look at
them carefully you will notice that some of them do
not twinkle as others do. They simply glow without
any flicker just as the moon shines.
Along with these bright objects, you may also see
the moon on most of the days. It may, however, appear
at different times, in different shapes and at different
positions. You can see the full moon only once in about
a month’s time. It is Full moon night or Poornima. A
fortnight later, you cannot see it at all. It is a New
moon night or Amavasya. On this day, you can watch
the night sky best, provided it is a clear night.
Do you wonder why can’t we see the moon and all
those bright tiny objects during day time? It is because
the very bright light of the sun does not allow us to see
all these bright objects of the night sky.
The sun, the moon and all those objects shining in
the night sky are called celestial bodies.
Some celestial bodies  are very big and hot. They
are made up of gases. They have their own heat and
light, which they emit in large amounts. These celestial
bodies are called stars. The sun is a star.
Countless twinkling stars in the night sky are
similar to the sun. But we do not feel their heat or
light, and they look so tiny because they are very very far
from us.
1
1
Let’s Do
You’ll need : 1 torch,
1 sheet of plain
paper, pencil and a
needle.
Step :
1. Place the torch in the centre
of the paper with its glass
front touching the paper.
2. Now draw a circle around
the torch.
3. Perforate the paper with the
needle within the circled
area.
4. Now place the perforated
circle part of the paper on
the glass front and wrap the
paper around the torch
with a rubber band.
5. Take care that the switch
of the torch is not covered.
6. In a dark room, stand at
some distance facing a
plain wall. Switch off all
other lights. Now flash the
torch light on the wall. You
will see numerous dots of
light on the wall, like stars
shine in the night.
7. Switch on all the lights in
the room. All dots of light
will be almost invisible.
8. You may now compare the
situation with what happens
to the bright objects of the
night sky after the sun rises
in the morning.
Rationalised 2023-24
2
THE EARTH : OUR HABITAT
Figure 1.1 : Saptarishi and the
North Star
You must have noticed that all
objects look smaller when seen from a
distance. How small an aeroplane looks
when it is flying at a great height!
While watching the night sky, you
may notice various patterns formed by
different groups of stars. These are
called constellations. Ursa Major or
Big Bear is one such constellation. One
of the most easily recognisable
constellation is the Saptarishi (Sapta-
seven, rishi-sages). It is a group of seven
stars (Figure 1.1) that forms a part of
Ursa Major Constellation. Ask someone
elder in your family or neighbourhood
to show you more stars, planets and
constellations in the sky.
In ancient times, people used to
determine directions during the night
with the help of stars. The North star
indicates the north direction. It is also
called the Pole Star. It always remains
in the same position in the sky. We can
locate the position of the Pole Star with
the help of the Saptarishi. Look at
Figure 1.1. You will notice that, if an imaginary line is
drawn joining the pointer stars and extended further,
it will point to the Pole Star.
Some celestial bodies do not have their own heat
and light. They are lit by the light of the stars. Such
bodies are called planets. The word ‘planet’ comes from
the Greek word “Planetai” which means ‘wanderers’.
The earth on which we live is a planet. It gets all its
heat and light from the sun, which is our nearest star.
If we look at the earth from a great distance, say the
moon, it will appear to be shining just as the moon.
The moon that we see in the sky is a satellite. It is a
companion of our earth and moves round it. Like our
earth, there are seven other planets that get heat and
light from the sun. Some of them have their moons too.
THE SOLAR SYSTEM
The sun, eight planets, satellites and some other
celestial bodies known as asteroids and meteoroids
Interesting Fact
Jupiter, Saturn and
Uranus have rings
around them. These
are belts of small debris.
These rings may be
seen from the earth
with the help of powerful
telescopes.
Rationalised 2023-24
3
THE EARTH IN THE SOLAR SYSTEM
1. MERCURY - One orbit around sun - 88 days,
One spin on axis - 59 days.
2. VENUS - One orbit around sun - 255 days.
One spin on axis - 243 days
3. EARTH - One orbit around sun - 365 days.
One spin on axis - 1 day
Number of moons - 1
4. MARS - One orbit around sun - 687 days
One spin on axis - 1 day,
number of moons - 02
5. JUPITER - One orbit around sun - 11 years, 11
months about 12 years. One spin on
axis - 9 hours, 56 minutes, number of
moons - about 53
6. SATURN - One orbit around sun - 29 years, 5
months. One spin on axis - 10 hours 40
minutes, number of moons - about 53.
7. URANUS - One orbit around sun - 84 years. One
spin around axis - 17 hours 14 minutes,
number of moons - about 27.
8. NEPTUNE - One orbit around sun - 164 years.
One spin on axis-16 hours 7
minutes, number of moons - 13.
Inner planets - very close to the sun. They are made up
of rocks.
Outer Planets - Very-very far from the sun and are huge planets made up of gases and liquids.
Figure 1.2 : The Solar System Saurce: https://planetarynames.wr.usgs.gov/Page/Planets
Rationalised 2023-24
4
THE EARTH : OUR HABITAT
form the solar system. We often call it a solar family,
with the sun as its Head.
The Sun
The sun is in the centre of the solar system. It is huge
and made up of extremely hot gases. It provides the
pulling force that binds the solar system. The sun is
the ultimate source of heat and light for the solar
system. But that tremendous heat is not felt so much
by us because despite being our nearest star, it is far
away from us. The sun is about 150 million km away
from the earth.
Planets
There are eight planets in our solar system. In order of
their distance from the sun, they are: Mercury,
Venus, Earth, Mars, Jupiter, Saturn, Uranus and
Neptune.
An easy way to memorise the name of the planets in
order of their distance from the sun is:
MY VERY EFFICIENT MOTHER JUST SERVED US NUTS.
All the eight planets of the solar system move
around the sun in fixed paths. These paths are
elongated. They are called orbits. Mercury is nearest
to the sun. It takes only about 88 days to complete
one round along its orbit. Venus is considered as
‘Earth’s-twin’ because its size and shape are very much
similar to that of the earth.
Till recently (August 2006), Pluto was also
considered a planet. However, in a meeting of the
International Astronomical Union, a decision was
taken that Pluto like other celestial objects (Ceres, 2003
UB
313
) discovered in recent past may be called
‘dwarf planets.”
The Earth
The earth is the third nearest planet to the sun. In
size, it is the fifth largest planet. It is slightly flattened
at the poles. That is why, its shape is  described as a
Geoid. Geoid means an earth-like shape.
Word Origin
Many words used
in a language may
have been taken
from some other language.
Geography, for example, is
an English word. It has its
origin in Greek, which
relates to the description
of the earth. It is made of
two Greek words, ‘ge’
meaning’ ‘earth’ and
‘graphia’ meaning ‘writing’.
Find out more about the
earth.
Do you know?
‘Sol’ in Roman
mythology is
the ‘Sungod’.
‘Solar’ means
‘related to the sun’. The
family of the sun is,
therefore, called the solar
system. Write down as
many words using the word
solar on your own as you
can.
Do you know?
Humans have
always been
fascinated gazing at the night
sky. Those who study the
celestial bodies and their
movements are called
astronomers. Aryabhatta
was a famous astronomer of
ancient India. He said that
the moon and the planets
shine due to reflected
sunlight. Today, astronomers
all over the world are busy
exploring the universe.
Rationalised 2023-24
Page 5


THE EARTH IN THE SOLAR SYSTEM
How wonderful it is to watch the sky after sunset! One
would first notice one or two bright dots shining in
the sky. Soon you would see the number increasing.
You cannot count them any more. The whole sky is
filled with tiny shining objects – some are bright, others
dim. It seems as if the sky is studded with diamonds.
They all appear to be twinkling. But if you look at
them carefully you will notice that some of them do
not twinkle as others do. They simply glow without
any flicker just as the moon shines.
Along with these bright objects, you may also see
the moon on most of the days. It may, however, appear
at different times, in different shapes and at different
positions. You can see the full moon only once in about
a month’s time. It is Full moon night or Poornima. A
fortnight later, you cannot see it at all. It is a New
moon night or Amavasya. On this day, you can watch
the night sky best, provided it is a clear night.
Do you wonder why can’t we see the moon and all
those bright tiny objects during day time? It is because
the very bright light of the sun does not allow us to see
all these bright objects of the night sky.
The sun, the moon and all those objects shining in
the night sky are called celestial bodies.
Some celestial bodies  are very big and hot. They
are made up of gases. They have their own heat and
light, which they emit in large amounts. These celestial
bodies are called stars. The sun is a star.
Countless twinkling stars in the night sky are
similar to the sun. But we do not feel their heat or
light, and they look so tiny because they are very very far
from us.
1
1
Let’s Do
You’ll need : 1 torch,
1 sheet of plain
paper, pencil and a
needle.
Step :
1. Place the torch in the centre
of the paper with its glass
front touching the paper.
2. Now draw a circle around
the torch.
3. Perforate the paper with the
needle within the circled
area.
4. Now place the perforated
circle part of the paper on
the glass front and wrap the
paper around the torch
with a rubber band.
5. Take care that the switch
of the torch is not covered.
6. In a dark room, stand at
some distance facing a
plain wall. Switch off all
other lights. Now flash the
torch light on the wall. You
will see numerous dots of
light on the wall, like stars
shine in the night.
7. Switch on all the lights in
the room. All dots of light
will be almost invisible.
8. You may now compare the
situation with what happens
to the bright objects of the
night sky after the sun rises
in the morning.
Rationalised 2023-24
2
THE EARTH : OUR HABITAT
Figure 1.1 : Saptarishi and the
North Star
You must have noticed that all
objects look smaller when seen from a
distance. How small an aeroplane looks
when it is flying at a great height!
While watching the night sky, you
may notice various patterns formed by
different groups of stars. These are
called constellations. Ursa Major or
Big Bear is one such constellation. One
of the most easily recognisable
constellation is the Saptarishi (Sapta-
seven, rishi-sages). It is a group of seven
stars (Figure 1.1) that forms a part of
Ursa Major Constellation. Ask someone
elder in your family or neighbourhood
to show you more stars, planets and
constellations in the sky.
In ancient times, people used to
determine directions during the night
with the help of stars. The North star
indicates the north direction. It is also
called the Pole Star. It always remains
in the same position in the sky. We can
locate the position of the Pole Star with
the help of the Saptarishi. Look at
Figure 1.1. You will notice that, if an imaginary line is
drawn joining the pointer stars and extended further,
it will point to the Pole Star.
Some celestial bodies do not have their own heat
and light. They are lit by the light of the stars. Such
bodies are called planets. The word ‘planet’ comes from
the Greek word “Planetai” which means ‘wanderers’.
The earth on which we live is a planet. It gets all its
heat and light from the sun, which is our nearest star.
If we look at the earth from a great distance, say the
moon, it will appear to be shining just as the moon.
The moon that we see in the sky is a satellite. It is a
companion of our earth and moves round it. Like our
earth, there are seven other planets that get heat and
light from the sun. Some of them have their moons too.
THE SOLAR SYSTEM
The sun, eight planets, satellites and some other
celestial bodies known as asteroids and meteoroids
Interesting Fact
Jupiter, Saturn and
Uranus have rings
around them. These
are belts of small debris.
These rings may be
seen from the earth
with the help of powerful
telescopes.
Rationalised 2023-24
3
THE EARTH IN THE SOLAR SYSTEM
1. MERCURY - One orbit around sun - 88 days,
One spin on axis - 59 days.
2. VENUS - One orbit around sun - 255 days.
One spin on axis - 243 days
3. EARTH - One orbit around sun - 365 days.
One spin on axis - 1 day
Number of moons - 1
4. MARS - One orbit around sun - 687 days
One spin on axis - 1 day,
number of moons - 02
5. JUPITER - One orbit around sun - 11 years, 11
months about 12 years. One spin on
axis - 9 hours, 56 minutes, number of
moons - about 53
6. SATURN - One orbit around sun - 29 years, 5
months. One spin on axis - 10 hours 40
minutes, number of moons - about 53.
7. URANUS - One orbit around sun - 84 years. One
spin around axis - 17 hours 14 minutes,
number of moons - about 27.
8. NEPTUNE - One orbit around sun - 164 years.
One spin on axis-16 hours 7
minutes, number of moons - 13.
Inner planets - very close to the sun. They are made up
of rocks.
Outer Planets - Very-very far from the sun and are huge planets made up of gases and liquids.
Figure 1.2 : The Solar System Saurce: https://planetarynames.wr.usgs.gov/Page/Planets
Rationalised 2023-24
4
THE EARTH : OUR HABITAT
form the solar system. We often call it a solar family,
with the sun as its Head.
The Sun
The sun is in the centre of the solar system. It is huge
and made up of extremely hot gases. It provides the
pulling force that binds the solar system. The sun is
the ultimate source of heat and light for the solar
system. But that tremendous heat is not felt so much
by us because despite being our nearest star, it is far
away from us. The sun is about 150 million km away
from the earth.
Planets
There are eight planets in our solar system. In order of
their distance from the sun, they are: Mercury,
Venus, Earth, Mars, Jupiter, Saturn, Uranus and
Neptune.
An easy way to memorise the name of the planets in
order of their distance from the sun is:
MY VERY EFFICIENT MOTHER JUST SERVED US NUTS.
All the eight planets of the solar system move
around the sun in fixed paths. These paths are
elongated. They are called orbits. Mercury is nearest
to the sun. It takes only about 88 days to complete
one round along its orbit. Venus is considered as
‘Earth’s-twin’ because its size and shape are very much
similar to that of the earth.
Till recently (August 2006), Pluto was also
considered a planet. However, in a meeting of the
International Astronomical Union, a decision was
taken that Pluto like other celestial objects (Ceres, 2003
UB
313
) discovered in recent past may be called
‘dwarf planets.”
The Earth
The earth is the third nearest planet to the sun. In
size, it is the fifth largest planet. It is slightly flattened
at the poles. That is why, its shape is  described as a
Geoid. Geoid means an earth-like shape.
Word Origin
Many words used
in a language may
have been taken
from some other language.
Geography, for example, is
an English word. It has its
origin in Greek, which
relates to the description
of the earth. It is made of
two Greek words, ‘ge’
meaning’ ‘earth’ and
‘graphia’ meaning ‘writing’.
Find out more about the
earth.
Do you know?
‘Sol’ in Roman
mythology is
the ‘Sungod’.
‘Solar’ means
‘related to the sun’. The
family of the sun is,
therefore, called the solar
system. Write down as
many words using the word
solar on your own as you
can.
Do you know?
Humans have
always been
fascinated gazing at the night
sky. Those who study the
celestial bodies and their
movements are called
astronomers. Aryabhatta
was a famous astronomer of
ancient India. He said that
the moon and the planets
shine due to reflected
sunlight. Today, astronomers
all over the world are busy
exploring the universe.
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5
THE EARTH IN THE SOLAR SYSTEM
Conditions favourable to support life are probably
found only on the earth. The earth is neither too hot
nor too cold. It has  water and air, which are very
essential for our survival. The air has life-supporting
gases like oxygen. Because of these reasons, the earth
is a unique planet in the solar system.
From the outer space, the earth appears blue
because its two-thirds surface is covered by water. It
is, therefore, called a blue planet.
The Moon
Our earth has only one
satellite, that is, the
moon. Its diametre is
only one-quarter that of
the earth. It appears so
big because it is nearer to
our planet than other
celestial bodies. It is
about 3,84,400 km away
from us. Now you can
compare the distance of
the earth from the sun
and that from the moon.
The moon moves around the earth in about 27 days.
It takes exactly the same time to complete one spin. As
a result, only one side of the moon is visible to us on
the earth.
The moon does not have conditions favourable for
life. It has mountains, plains and depressions on its
What do animals and
plants require in order
to grow and survive?
Figure 1.3 : The moon as seen from
the space
Do you know?
Light travels at
the speed of
about 300,000
km per second.
Yet, even with this speed,
the light of the sun takes
about eight minutes to
reach the earth.
Interesting Fact
Neil Armstrong was
the first man to
step on the surface
of the moon on 20 July
1969. Find out whether
any Indian has landed on
the moon?
A Satellite is a celestial
body that moves around
the planets in the same
way as the planets move
around the sun.
A Human-made Satellite
is an artificial body. It is
designed by scientists to
gather information about
the universe or for
communication. It is
carried by a rocket and
placed in the orbit around
the earth.
Some of the Indian
satellites in space are INSAT,
IRS, EDUSAT, etc.
Figure 1.4 : Human-made Satellite
Rocket launch Rocket falls back to the Earth Satellite enters orbit
? ?
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