The Earth And The Solar System

 THE SOLAR SYSTEM


The family of the sun is known as the solar system. It consists of the sun, eight planets, about 100 known satellites, like the moon, and asteroids, meteors and comets.

The solar system is a section of the Milky Way galaxy. It is about 27,000 light years away from the centre of the Milky Way galaxy. The solar system is about 470 crore years old and is about 1.200 crore km wide.


THE SUN

The sun is the largest member of the solar system and is located at its centre. 

The diameter of the sun is approx 109 times greater than the diameter of the earth. The sun is the main source of heat and light for all types of life on earth.

That is why, ancient people always worshipped the sun as a god. The sun is at an average distance of about 15 crore km from the earth. The brilliant disc of the sun, that is seen from the earth, is called the photosphere




The temperature at the surface of the sun is about 6,000 C, while at the centre of the sun, it is about 1,50,000,000 °C. The light from the sun, travelling at a speed of 3,00,000 km per second, takes about 8 minutes and 20 seconds to reach the surface of the earth.


The gravitational pull of the sun keeps all the members of the solar system together.

The light coming from the sun is very strong We should not look directly at the bright sun with naked eyes, particularly through a telescope or binoculars. This can damage the eyes

THE PLANETS

There are eight planets in the solar system. According to  their distance from the sun, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.The eight planets in order of their decreasing size are Jupiter, Saturn, Uranus. Neptune, Earth, Venus, Mars and Mercury. The planets are generally classified into two groups




Inner Planets Mercury, Venus, Earth and Mars are the inner planets. These four planets are close to the sun and are made up of rocks Thus, they are also called terrestrial planets, Le the earth-like planets.


Outer Planets Jupiter, Saturn, Uranus and Neptune are the outer planets. They are called


gas giants, as they are made up of gases. 




The planets are heavenly bodies.


They do not have their own heat and light.


They shine, as they reflect the light of the sun.


 All the planets are spherical in shape. 


They revolve around the sun in elliptical paths called orbits.


They move around the sun from west to east.


While revolving around the sun, the planets also rotate on their axes.


Each planet takes a different time to complete one revolution around the sun and one rotation on its axis.




OUR PLANET-THE EARTH




The earth is the third planet from the sun and is the fifth largest in the solar system. It is the largest among the inner planets. The earth is our home. It is unique in the solar system.


Its uniqueness is due to 


the best location, with reference to the sun.


Favourable environmental conditions for the origin and survival of various forms of life.


the rotation of the earth on its axis keeps the extremes of temperature between day and night within tolerable limits.




A favourable temperature for the existence of life. (If the heat received from the sun was to increase or decrease by about 10 per cent, a large part of the earth would become unfit for living organisms.)


The range of temperature on the surface of the earth, wherein water can remain in its three forms-ice, water and vapour.




the presence of adequate water in the oceans, which provides ideal conditions for the origin and evolution of life.




 The presence of an atmosphere, which protects the earth from harmful ultraviolet radiations coming from the sun. 


the oxygen-rich atmosphere, which is necessary for the survival of human beings and other forms of life.




The earth is the only planet in the solar system, which is not named after a mythological deity. The symbol of our planet is a circle containing two lines perpendicular to each other. It represents the intersection of the equator and the Prime Meridian.


When astronauts first saw the earth from space, it looked blue in colour due to the presence of water all over it. So, the earth is also called the watery planet or the blue planet.




. In ancient times, people thought that the earth was flat in shape. .


 Aristotle and then Copernicus declared that the earth is spherical in shape.


Actually, the earth is not a perfect sphere 


Due to the rotation of the earth, it is slightly bulging at the equator and flattened at the poles.


Thus, its equatorial diameter is about 44 k more than its polar diameter.




OTHER PLANETS IN THE SOLAR SYSTEM




Mercury is named after the messenger of Roman gods. It is closest to the sun. There is great difference between the day temperatur (about 400 °C) and the night temperature (about -170 °C). It has no moon.




Venus is named after the Roman god of love and beauty. It is the second planet from the sun. It is almost the same size as the earth and is known as the 'Earth's Twin'. It is visible after sunset (Evening Star) or before sunrise (Morning Star). It is very hot and has no moon.


Mars is named after the Roman god of war. It is known as the 'Red Planet'. Mars is about half the size of earth. It has almost the same period of rotation as the earth. It has two moons.


Jupiter is named after the ruler of the Roman gods. It is the largest planet in the solar system. Jupiter, with its 39 known moons, is often described by National Aeronautics and Space Administration (NASA) as a mini solar system.

Saturn is named after Jupiter's father in Roman mythology, It is the most beautiful planet in the solar system. It has bright rings made of icy particles around its equator. Saturn, according to NASA, has 32 known moons.

Uranus is named after the Greek god of the sky. It was discovered in 1781 by William Herschel. Uranus also has rings around its equator. According to NASA, it has 21 known moons.

Neptune is named after the Roman god of the sea. It is similar to Uranus in size and structure. The two are called the Twin Giants". Neptune has eight known moons.

THE SATELLITES

The word 'satellite means an attendant or a companion.

The moon was the only known satellite in the solar system until 1610.

Today, there are more than 100 known satellites in the solar system.

Mercury and Venus are the only planets which do not have any known satellite 

The satellites move around the planets from west to east

The satellites do not have their own light they reflect the light of the sun,

THE MOON

The moon is the heavenly body which is closest to the earth.

The average distance of the moon from the earth is about 3.84,400 km. Its diameter is about 3,480 km.

The moon appears larger and brighter than any other celestial body in the night sky. The reflected light of the sun from the moon reaches the earth's surface in about 1.3 seconds. 

No life can exist on the moon due to the absence of atmosphere and moisture.

 There is no sound, as there is no air to carry the sound waves

The moon rotates on its axis and revolves around the earth from west to east. 

The time taken by the moon to complete one rotation and one revolution is the same. Thus, we always see the same face of the moon. 

The days on the moon are very hen (120°C) and the nights are very cold (-120 °C).

Two American astronauts, Neil Armstrong and Buzz Aldrin, landed on the moon on 21 July 1969. They explored and photographed the surface of the moon This was followed by several other attempts by USA and Russia.

Phases of the moon

We know that the moon reflects the light of the sun. Thus, the visible shape of the moon changes from night to night.

In its journey from New Moon to Full Moon, the visible portion increases and the moon is said to wax.

In its journey from Full Moon to New Moon, the visible portion decreases and the moon is said to wane.

The waxing and waning of the moon is known as the phases of the moon 

In fact, the moon is always half dark a half bright, but the angle of view from the earth keeps changing. 

On the New Moon day, the dark hemisphere of the moon faces the earth, whereas on the Full Moon day, the bright hemisphere is visible to us

ASTEROIDS

Asteroids are small planet-like solid objects found in the solar system. They are also called planetoids or minor planets.

Each asteroid follows its own orbit around the sun. 

The main belt, which has billions of asteroids, lies between the orbits of Mars and Jupiter. This belt stretches from about 250 million to 600 million km from the sun .

It is now widely believed that asteroids arr broken pieces of some planet, which probably esploded soon after its birth.

METEORS

Every night,we can see some bright streaks of light in the sky. These are called meteors.They are also known as shooting stars.

Meteors are small pieces of nocks revolving around the sun. 

The presence of meteors in the sky is known only when they enter the earth's atmosphere

Most of them bum up and become gases. 

Some of them are big and thus, are not bumt up completely.

When they hit the surface of the earth, they are called meteorites.

A well-known site is the Meteor Crater in Arizona state in USA

COMETS

It is believed that there are about 200 crore comets orbiting the sun.

Comets are huge lumps of snow and rocky dust. Each comet follows its own orbit around the sun. 

When comets reach near the sun, they start glowing and develop a long tail. The most famous comet is the Halley's comet. It was last seen in 1986. It will appear again after 76 years, ie in 2062.

THE CONSTELLATIONS

The constellations are groups of bright stars in the sky. The people of ancient civilizations attributed figures of animals, people and mythical beasts to these groups.

In ancient days, the constellations were believed to influence the daily life of people on earth.

The constellations were used as a guide for planting and harvesting crops and slaughtering animals The most easily recognizable constellation is the Saptarishi, which is a group of seven stars.

In ancient times, people used to find the north direction with the help of stars. The Pole Star indicates the north. We can locate the position of the Pole Star with the help of the Saptarishi.

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