7
The Earth And
Its Companions
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Learning Objectives
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After completing this chapter, you will be able to :
• name the planets in the solar system • know the shape of the Earth
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• describe rotation and revolution of the Earth • identify the phases of moon
• know about constellations and galaxy
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K Use Cordova Smart Class Software on the smart board in class to make learning enjoyable.
Identify the pictures and unscramble the words to write their names.
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RTAHE OMON ARTSS
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1. _______________ 2. _______________ 3. _______________
We live on a beautiful planet called the Earth. The Earth moves around the Sun.
There are seven other planets that also move around the Sun. These are Mercury,
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Venus, Mars, Jupiter, Saturn, Uranus and Neptune. This family of the Sun and the
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eight planets is called the solar system.
Mercury Venus Earth Mars
Saturn Uranus Neptune
Sun Jupiter
Solar system
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PLANETS
Planets do not have their own light. They reflect the light that falls on them from the
Sun. The planets revolve around the Sun in their fixed path called orbits. A satellite
is a heavenly body that revolves around the planets. Moon is the natural satellite of
the Earth.
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THE EARTH
The Earth is the only planet in the solar system where
From space, the
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life exists. The surface of the Earth is covered with Earth looks blue-
land and water. It is surrounded by a layer of air called green in colour due
atmosphere. The Earth gets heat and light from the to the presence of
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Sun. Air and water support life on the Earth. water and forests.
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SHAPE OF THE EARTH
The Earth looks flat to us. But it is not
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so. The Earth is round and bulging in the
middle, just like an orange. It is slightly
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flat at the two poles. When we see a ship
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sailing away from the seashore, its lower
The Earth is round.
part disappears first. Its top part is the
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last to disappear. This is because ship is sailing on a curved surface of the Earth, and
not on a flat surface.
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We also have photographs of the Earth taken by astronauts from spaceships.
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Astronauts are the people who go into the space.
The Earth is round but why does it look flat? The Earth is very big. We can see only a
small part of it. This small part appears flat to us. north pole
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MOVEMENTS OF THE EARTH
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axis
The Earth is moving all the time. It shows two types of movements:
(a) rotation (b) revolution
1. Rotation of the Earth
Earth
The Earth spins like a top on an imaginary line. This line passes
south pole
through the centre of the Earth vertically and joins the two poles The Earth spins like
(north pole and south pole). This line is called the axis. The spinning a top on its axis.
Science-3 (Term-2) 207
of the Earth on its own axis is called rotation. The Earth completes one rotation in
24 hours. This rotation causes day and night on the Earth.
Use Cordova Smart Class Software on the smart board in class to perform this activity.
Activity
To show how days and nights are caused
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Take a globe and a torch. Imagine that the globe is our Earth and the torch is the
Sun. Mark one side of the globe A and the other B.
Place the globe on a table in a dark room. Now, throw light from torch on side
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A of the globe. Half of the globe (side A) gets lighted. The other half (side B)
remains dark [Fig. (a)].
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In the same way, the part of the Earth that faces the Sun gets sunlight and has
day. At the same time, the other part of the Earth that does not get sunlight has
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night.
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B A
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Fig. (a)
Now, slowly spin the globe from left to right. The lighted side A of the globe
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moves away from the light and comes in dark. At the same time, the dark side B
of the globe receives the light and lights up [Fig. (b)].
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A B
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Fig. (b)
Look at the globe. You see that India is on the opposite side of America. So, when
it is day in India, it is night in America and when it is night in India, it is day in
America.
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2. Revolution of the Earth summer spring
While the Earth rotates on its axis, at
the same time, it also goes around
the Sun. The Earth follows a fixed
path during its journey around the
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Sun. This path is called the orbit of SUN
the Earth. The movement of the
Earth around the Sun in a fixed
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orbit is called revolution. The
Earth completes one revolution in
autumn winter
365¼ days. Revolution of the Earth
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Revolution of the Earth around the Sun
causes seasons.
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Multiple Choice Questions (MCQs)
Tick () the correct answers:
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1. The shape of our Earth is ........................ .
(a) round (b) flat (c) square
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2. Rotation of the Earth causes ........................ .
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(a) seasons (b) earthquakes (c) day and night
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THE SUN
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The Sun is like a big ball of hot gases and fire. It is a star closest to the Earth. The Sun
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has its own light and heat. The temperature of the Sun is about 5400°C. The Earth
and other planets get light and heat from the Sun.
THE MOON
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The moon is the only natural satellite of the Earth.
It is about 384,400 km away from the Earth. It takes
about 27.3 days to complete one rotation as well as
revolution around the Earth. The moon does not have
any light of its own. It reflects the light of the Sun and
we call this ‘moonlight’. There are huge holes on the
surface of the moon called craters. There is no air on Craters on moon
the moon.
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Phases of the Moon
Every night, the shape of the moon is different. However, the moon does not really
change its shape. Due to revolution of the moon around the Earth, the moon appears
to change its shape.
The day-to-day changes in the shape of the moon as seen from the Earth are called
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phases of the moon. We see that portion of the moon which is lighted due to the
sunlight.
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New Moon
When the moon is between the Earth and the Sun, we cannot see the
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moon at all. This is called new moon. It is dark on the new moon night.
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Crescent Moon
When we see a small sunlit portion of the moon, it is called crescent
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moon.
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Half Moon
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When we see half of the moon, it is called half moon.
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Gibbous Moon
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When we see more than half of the moon, it is called gibbous moon.
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Full Moon
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When we see complete moon, it is called full moon.
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Multiple Choice Questions (MCQs)
Tick () the correct answers:
1. The only natural satellite of the Earth is ........................ .
(a) star (b) Sun (c) moon
2. Holes on the moon’s surface are called ........................ .
(a) meteorites (b) craters (c) asteroids
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THE STARS
Stars are big heavenly bodies that have their own light.
Most of the stars are much bigger than our own Sun. But
they look so small because they are far away from the
Earth. We can observe stars with a telescope.
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Stars are there in the sky all the time. But we are able to
see them only at night. This is because during the day- Stars in the sky at night
time, the sunlight is brighter than the light of the stars.
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In the north, we can see a very bright star. It is called LEO (lion) ORION
(hunter)
the Pole Star (Dhruv Tara). It is the only stationary
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star in the sky. It helps to find the north direction. In
olden days, when there were no instruments like the
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magnetic compass, sailors used to take the help of
the Pole Star to find their ways.
K URSA MAJOR
(great bear)
SCORPIUS
(scorpion)
Some stars are arranged in groups and form patterns in
the sky. Such groups of stars are called constellations.
They form patterns of various animals and objects. Various constellations
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in the sky at night
There are about eighty eight different constellations.
Some of them are – Ursa Major (The Great Bear), Scorpius (Scorpion), Orion (Hunter)
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and Leo (Lion).
GALAXY
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The solar system, stars and constellations together form
a galaxy. Our solar system is in a galaxy, called the Milky
Way. It is spiral in shape. Our solar system is only a small
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part of the Milky Way galaxy. Milky Way galaxy
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Key Words
Solar system : family of the Sun and the eight planets
Astronauts : people who go into the space
Rotation : spinning of the Earth on its own axis
Revolution : movement of the Earth around the Sun in a fixed orbit
Satellite : heavenly body that revolves around a planet
Constellation : group of stars forming pattern in the sky
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E Very Short Answer Questions:
1. Name one constellation.
2. Write the names of the phases of the moon.
F Short Answer Questions:
1. What are craters?
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2. What is meant by the phases of the moon?
3. The Earth follows a fixed path during its revolution around the Sun.
(a) What is this fixed path called?
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(b) What do you learn from this act of the Earth? (Value Corner)
G Long Answer Questions:
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1. What is meant by rotation of the Earth? How much time does the Earth take to
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complete one rotation?
2. What is meant by revolution of the Earth? What does it cause?
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PICTURE TALK
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Identify the pictures and write their names in the spaces provided:
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1. ______________ 2. ______________ 3. ______________ 4. ______________
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Think And Answer
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1. How many hours will be there in one whole day (one day and one night), if the
Earth completes its one rotation in 28 hours?
2. If we see a new moon on January 1, then on which date can we see a full moon?
Group Activity/Project : Collect information about some Indian astronauts like Rakesh
Sharma, Kalpana Chawla and Sunita Williams and write about them in your notebook.
Group Discussion : Discuss in the class: ‘The importance of movements of the Earth’
Science-3 (Term-2) 213
