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Sun – The star at the centre of the solar system is called sun.
The sun lies at the centre of our solar system.
It is about 150 million kilometres from the earth.
The sun, like other stars, is a sphere of hot glowing gases.
Temperature at the surface of sun is nearly 6000 degree centigrade.
Sun diameter is about 110 times wider than earth.
Around 74% of the sun mass is made up of hydrogen.
Earth – The planet on which we live is called Earth.
It has land, water, mountains, plains but it has not always been like this.
For millions of years, it kept on spinning.
As it spun, its outer surface grew cold and hard.
Some gases escaped, while some were trapped inside.
As a result, its outer surface became hard and the hot, molten material remained in its core.
After a period of millions of years, life was originated on the earth.
The first time we got a complete view of the earth was only in 1968, when Apollo 8 astronauts flew around the moon and saw the earth.
Structure of the earth –
Earth is a unique planet.
Earth is flattened at the poles and bluges at the equator.
Earth is also called a blue planet.
The blue colour is because of the oceans.
The white colour is due to the clouds and snow.
The brown patches make up the land.
The green colour is due to the plants.
Layers of the earth –
Crust
Mantle
Core
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Crust – The outermost layer of the Earth which is made up of soil and rocks are called crust.
Crust is made up of soil and rock.
It is the outermost layer of the earth.
It is around 5 kilometres thick under the sea level.
It 70 km thick below the continent.
Mantle – The second layer of the Earth which is made up of solid Rock materials are called mantle.
Mantle is made up of solid rock.
It containing minerals and metals.
It is about 2900 km thick.
Core – The innermost layer of the earth surface is called core.
The core of the Earth is very hot and under high pressure.
The liquids and gases in the core push against the outer crust.
Movement of the earth:-
Rotation
Revolution
Rotation – The movement of the Earth on its axis is called rotation.
The effect of rotation on the earth causes day and night.
The places on the earth that face the sun experience daytime.
While those facing away from the sun experience night time.
The earth complete one rotation in 24 hours.
Revolution – The movement of the earth around the sun in a fixed Orbit are called revolution.
The revolution of the earth around the sun causes different types of season.
The Earth takes 365 days and 6 hour to complete one revolution.
Axis – The imaginary line running through the earth from the North Pole to South Pole are called axis.
The earth axis is slightly tilted at an angle of 23.5 degrees.
Equator – An imaginary line which divides the earth horizontally into two equal halves are called Equator.
The two equal halves are Northern hemisphere and the southern hemisphere.
Northern hemisphere – The upper half between the equator and the North Pole is called the northern hemisphere.
Southern hemisphere – The lower half between the equator and the South Pole is called the southern hemisphere.
How Seasons are formed?
(a) When the North Pole is towards the sun:
It is summer in the northern hemisphere.
At the North Pole, there is sunlight throughout the day and the days are longer.
During this time the South Pole is turned away from the sun and has winter.
There is not much day light at the South Pole.
(b) When the North Pole is turned away from the sun:
It is winter in the northern hemisphere.
The days are shorter and nights are longer in the northern hemisphere.
It is summer in the southern hemisphere.
The region near the equator gets the same amount of sunlight all the year round.
It has summer throughout the year.
Days and nights are of about twelve hours each.
Solar System – The family of the sun, planets and their satellites together is known as the solar system.
There are 8 planets in the solar system.
It consists of Sun and all other object that travels around Sun.
These objects include planets, asteroids, meteoroids, natural satellites etc.
Our solar system is a part of the Milky Way galaxy.
Our galaxy is an elliptical Galaxy.
Planet – A very large round object in space that moves around the Sun or another star is called planet.
There are 8 planets in the solar system.
Planets do not have light of their own.
It reflects the sunlight that falls on them.
The Planet of the solar system is –
Mercury –
It is the closest planet to the sun.
It does not have an atmosphere to regulate the temperature.
It is boiling hot during the day and freezing cold at night.
It has no natural satellites.
Venus –
It is the brightest planet in the night sky and is called the evening star.
Venus has no atmosphere.
It is made up of carbon Dioxide, hence is the hottest known planet.
It has no natural satellite.
Earth –
Life exists on this planet.
It has an atmosphere which protects the earth.
It has water for survival.
It has one natural satellite known as the moon.
Mars –
It is called the red planet because it appears red.
It is covered by red dust.
Mars has two natural satellites or moons called Demo and Phobes.
There is a mountain on Mars, and it is twice the size of Mount Everest.
It is known as Olympus Mons.
Jupiter –
It is the largest and fastest spinning planet in the solar system.
It has 66 moons or natural satellites.
Jupiter is made up of gas and has a red spot on it.
Red spot is a storm and is clearly visible from the earth through a telescope.
Jupiter is so large that we could fit 1000 earths in it.
Saturn –
It is the sixth planet in the solar system.
It can be identified by the rings around it.
It rings are made up of rocks, ice and dust.
It has 62 moons or natural satellites.
It is the lightest planet in the solar system.
The largest moon of Saturn is called Titan.
Uranus –
It is the seventh planet in the solar system.
It is covered by a green blue gas.
It has 27 moons or natural satellites.
Neptune –
It is the farthest planet in the solar system.
It has cold winds that blow at very high speed.
It has 13 moons revolving around it.
Pluto –
It is no longer included in the list of planets.
In 2006 it was classified as a dwarf planet.
Satellite – The heavenly body which revolve around planet in fixed Orbit are called satellite.
The entire planet except Mercury and Venus has satellites.
The moon is a natural satellite of the earth.
The rotation and the revolution of the Moon around the earth cause phases of the Moon.
Types of satellite:-
Natural satellites
Artificial satellites
Natural satellites – Any celestial body in space that orbits around a larger body are called natural satellites.
Moon is the only natural satellite of the earth.
The moon takes 27 days to complete one Revolution around the earth.
It does not have it own light but reflect the light of the Sun.
It does not have an atmosphere to protect itself from extreme heat or cold.
It may be very hot in the day and very cold at night.
Artificial satellites – An artificial object that is manufactured by humans and launched into the Earth’s orbit are called artificial satellites.
There are many artificial satellites revolving around the earth.
They are all manmade and have been sent into space by rockets.
The first artificial satellite was Sputnik 1 launched by Russia in 1957.
Aryabhatta was the first artificial satellite sent by India in 1975.
Constellation – A group of stars in the sky appear to form a shape of pattern is called constellation.
There are about 88 constellations in the sky.
Example – Orion, Scorpio, USA major
