The Earth in the Solar System { CBSE Class 6th Geography }
Today we will study about our Earth and Solar System. The sun shines during the day. In the night,
the sky is dotted with numerous bodies that shine
and twinkle. The moon also appears at night. All
these bodies appear to us hanging up in space
which the ancient people called ‘Heaven’. Our own earth is also a part of this system
and thus it is also called a heavenly body or a
celestial body.
These heavenly bodies are grouped as stars,
planets, satellites and asteroids.
Stars
These are self-luminous bodies. It
means they have their own heat and light. Stars are
made of hot, burning gases. They are usually very
big in size but as they are very far away from us,
they look small and tiny like little dots in the sky.
Our sun is also a star. It looks bigger and brighter
because, compared to other stars, it is much nearer
to our earth. Groups of stars, forming a
particular pattern, are called constellations. One
such constellation is a group of seven stars which
is called the Saptarishi.
The Saptarishi are regarded as very important
because in ancient times they used to guide the
sailors at night. Stars are very far off from our earth. The light
from the stars passes through different layers of the
atmosphere with varying densities. As a result,
they seem to be twinkling.
Stars are so far off from us that we cannot
understand or express this distance in kilometres or miles. We express this great distance in terms of
light years. Light travels at a tremendous speed of
about 3,00,000 kilometres per second. The
distance that light travels in a year is called a light
year.
The Solar System
The solar system means
the ‘Family of the Sun’. The sun and the eight
planets that revolve round the sun are members of
the solar system. The eight planets are —Mercury,
Venus, Earth, Mars, Jupiter, Saturn, Uranus, and
Neptune. Besides the sun and the planets, there
are some smaller celestial bodies as well in the
solar system.
The Sun
The sun is the biggest member of
the solar family. All the planets and satellites, etc.
revolve round the sun. It is the center of the solar system. It is about 13,00,000 times
bigger than our earth. The sun is made up of extremely hot gases
and it gives out a lot of heat and light which is the
source of all energy in the solar system. Our earth
gets only a part of the energy. Without the sun’s
energy, our earth would become cold and lifeless.
It is the sun which sustains all life.
Planets
There are eight planets in our
solar system. They, according to their distance
from the sun, are—Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus and Neptune.
Venus is the hottest. Planets can also be rated according to their
size. In the ascending order, they are— Mercury,
Mars, Venus, Earth, Neptune, Uranus, Saturn and
Jupiter.
In this way, the largest planet in our solar
system is Jupiter while the smallest planet is
Mercury. The planets revolve round the sun in fixed
paths which are called their orbits. They also
rotate on their own axis. All the planets move round the sun in the same direction but they do
not take the same time to complete a revolution.
A planet which is nearer the sun takes less time
than the one which is farther from the sun.
Earth
Our earth is also a planet because it revolves
round the sun. It completes one revolution round
the sun in 365¼ days. In size, it ranks fifth after
Jupiter, Saturn, Uranus and Neptune. If you see it from the outer space, it looks blue
in color. It is because of the presence of water in its oceans and seas. It is, therefore, sometimes
called the blue planet.
In fact our earth is a unique
planet in the whole solar system because climate which is best
suited for the development of man and
other forms of life on the earth. Its atmosphere is rich in oxygen that
makes life possible on this planet. On this planet water occurs in
vast quantities which makes life possible
on the earth.
Shape of the Earth
Earlier it was believed
that the earth was flat but later on scientists proved
beyond doubt that it is not flat but spherical in
shape. The pictures of the earth, as
taken by different astronauts
who went into outer space,
show that the earth is
spherical in shape. It is argued that sailors like Magellan and
Drake, who sailed round the world,
started from one point and sailing in the
same direction, at last reached the same spot. If the earth had been flat they would
have reached some abrupt edge.
Satellites
A satellite moves round the
planet in the same way as a planet
moves round the sun. In other words,
while revolving round the planet, the
satellites also revolve round the sun.
Our earth has one satellite which we
call Moon while Uranus has 27
satellites and Neptune 14 satellites.
Mercury and Venus have no Satellites. Satellites, like the planets, have no light
or heat of their own. They reflect the light of the
sun. There are some differences between them.
While planets revolve round the sun, the satellites
revolve round the planets. For example, the earth
revolves round the sun, but the moon (a satellite)
moves round the earth.
The Moon
Earth’s satellite is known as the
moon. Its diameter is about one fourth of the
earth’s diameter and it is about 3,84,000 km away
from the earth. It has no light of its own. It reflects
the sun’s light which reaches the earth in one and
a quarter seconds. The moon does not look the
same every night. It keeps on changing its face
every night. As discussed above, it has no light of
its own and it simply reflects the light of the sun.
The moon completes its revolution around the
earth in 29 days and 8 hours. It is called a lunar
month. It also completes its rotation on its own
axis in the same time. As a result, it shows only
one side to us while the other side of the moon
remains away from us. An American astronaut, Neil
Armstrong, was the first man to land on the moon. They all show that the
moon’s surface is very rough and uneven. There is
no air or water on the moon and it is very hot
during the day while the nights are very cold. As
a result, there is no life on the moon.
Other Celestial Bodies
Besides the planets and satellites, there are
numerous other small celestial bodies which move
around the sun. They are known as asteroids,
meteors and comets.
Asteroids :--They are very small planet-like
bodies which revolve around the sun between the
orbits of Mars and Jupiter. Meteors :-- Meteors are small pieces of solid
mass which move about in the sky, revolving around the sun. Sometimes they enter the earth’s
atmosphere with great speed. They become heated
by friction and start burning. That is why
sometimes meteors are also called Shooting Stars. Comets :-- There is another category of
heavenly bodies known as comets. They too move
around the sun, but they follow long elongated
orbits. They appear as beautiful shining bodies in
the sky with long tails.
India’s Space Programme
India’s space programme began in 1975 with
the launching of Aryabhatta, the first Indian
satellite, into space with the help of Russia. Then
two other satellites, namely, Bhaskara I and
Bhaskara II, were sent into space in 1979 and
1981 respectively with Soviet help. After this,
India with the help of U.S.A. launched INSAT-1A
and INSAT-1B into space in 1983. The launching
of INSAT-1B proved quite successful. Then in
1984 Squadron Leader Rakesh Sharma was sent
into space along with two other Russian
cosmonauts.
The artificial satellites have proved very useful
in telecommunication, meteorology, T.V. relay and
broadcasting. In a single day in June, 2016 ISRO launched
20 satellites into space, most of them foreign. In
2014, Indian space vehicle Mangalyaan was
launched into the orbit of Mars to carry out
explorations and discoveries. INSAT- 3DR, the
most advanced meteorological satellite of India
was launched by GSLV-FO5.
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