Celestial Bodies
The sun, the moon and all those natural objects shining or moving in the night sky are called celestial bodies.
The Star
The very big and hot celestial gases bodies which emit in large amounts of their own heat and light are called stars. The sun is a star. Thus the sun is our nearest star.
Q. Why do We not feel the heat or light of twinkling stars?
Ans. We do not feel the heat or light of twinkling stars because they are very very far from us.
Q. Why does the stars look so tiny?
Ans. The stars look so tiny because they are very very far from us.
Constellations
The recognisable patterns formed by stars in the night sky are called constellations. Ursa Major or Big Bear is one such constellation.
Pole Star
The North star indicates the direction of the north pole of the earth. So it is also called the Pole Star.
It always remains in the same position in the sky. In ancient times, people used to determine directions during the night with the help of stars.
We can locate the position of the Pole Star with the help of the Saptarishi. We will notice that, if an imaginary line is drawn joining the pointer stars and extended further, will point out to the Pole Star.
Saptarishi
One of the most easily recognisable constellation is the Saptarishi (Sapta seven, rishi-sages). It is a group of seven stars that forms a part of Ursa Major Constellation.
Planets
The celestial bodies movie around the sun (star) and do not have their own heat and light. They are lit by the light of the stars. Such bodies are called planets. The earth on which we live is a planet.
The word 'planet' comes from the Greek word "Planetai" which means 'wanderers.
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.
Like our earth, there are seven other planets that get heat and light from the sun. Some of them have their moons too.
A Satellite is a celestial body that moves around the planets in the same way as the planets move around the sun.
Satellite –> A celestial body revolving around a planet in the same way as the planets move around the sun is called a satellite. Satellite are of two types
1. Natural satellite
2. Artificial or Man-made satellite
1. Natural Satellite –> An Natural satellite is an yenatural object that continuously moves in the orbit of the Earth or some other celestial body in space.
★ Moon is a natural satellite of the earth.
2. Artificial Satellite –> An artificial satellite is a man-made object that continuously moves in the orbit of the Earth or some other celestial body in space.
Moon
The moon that we see in the sky is a satellite. It is a companion of our earth and moves round it. The moon does not have conditions favourable for life. It has mountains, plains and depressions on its surface. These cast shadows on the moon's surface. Look at the full moon and observe these shadows.
Moon is Earth's closest neighbour in space. Moon is the natural satellite of Earth. A satellite is a heavenly object which revolves around a planet. It is held in its orbit by Earth's gravity. It is about 3,84,400 km away from Earth.
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.
Q. Being a satellite, it has no light of its own. Have you ever wondered how then does it shine?
Ans. Moon does not have light of its own. It reflects the light of sun falling on it.
The Phases of Moon
Moon appears to be changing shape everyday. It appear at different times, in different shapes and at different positions. These different shapes of Moon as visible from Earth are called phases of Moon.
The shape during a particular phase depends on reflecting light of sun falling on the part that can be seen by us on Earth.
Full moon night or Poornima
We can see the full moon only once in about a month's time. It is called Full moon night or Poornima.
No moon night or Amavasya
We cannot see the moon in the sky only once in about a month's time. It is called No moon night or Amavasya.
A fortnight
The time period or time duration between Poornima (Full moon night) to Amavasya (No moon night) or vise versa. A fortnight is about to 14 or 15 days.
Q. How do we always see the same side of Moon from Earth?
Ans.
The moon moves around the earth in about 27 days. Moon also rotates on its axis once in about 27 days. Since it takes exactly the same time (about 27days) to complete one rotation (spin) and one revolution (round). As a result, only same side of the moon is visible to us on the earth.
Q. Do you wonder why can't we see the moon and all those bright tiny objects during day time?
Ans. We cannot see the moon and all the bright tiny objects during day time, because the very bright light of the sun does not allow us to see all these bright objects of the night sky in the day.
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.
THE SOLAR SYSTEM
The sun, eight planets, satellites and some other celestial bodies known as asteroids and meteoroids form the solar system. We often call it a solar family, with the sun as its Head.
The Sun
'Sol' in Roman mythology is the 'Sungod'. 'Solar' means 'related to the sun'. The family of the sun is, therefore, called the solar system.
The sun is huge hot ball and made up of extremely hot gases. It is the ultimate source of heat and light for the solar system.
The sun is in the centre of the solar system. It is about 150 million km away from the earth.
It provides the pulling force that binds the solar system.
Q. We do not feel the tremendous heat of the Sun?
Ans. The tremendous heat of the sun is not felt so much by us because despite being our nearest star, it is about 150 million km far away from us.
Special for solar system
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.
Orbits
All the eight planets of the solar system move around the sun in an elongated fixed paths. These elongated fixed paths are called orbits.
Mercury is nearest to the sun. It takes only about 88 days to complete one round along its orbit.
Q. Why does Venus considered as 'Earth's-twin?
Ans. Venus is considered as 'Earth's-twin' because its size and shape are very much similar to that of the earth.
Q. Why did the Pluto remove from planet family.
Ans. Till recently (August 2006), Pluto was also considered as a planet.
But, in a meeting of the International Astronomical Union, a decision was taken that Pluto like other celestial objects (Ceres, 2003 UB) 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.
Q. What are favourable Conditions to support life on the earth?
Or
Why the earth is a unique planet in the solar system ?
Or
Q. What do animals and plants require in order to grow and survive?
Ans. 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.
Q. What is the speed of the light? How much times takes the light of the sun to reach on the earth?
Ans. 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.
Q. From the outer space, the earth appears blue, why ?
Or
Why the earth is called blue planet?
Ans. From the outer space, the earth appears blue because its two-thirds surface is covered by water. It is, therefore, called a blue planet.
Word Origin
Words used in geography have been taken from some other language.
For example, Geography, is an English word. It has its origin in Greek, which relates to the description of the earth.
It is made up of two Greek words, 'geo' meaning' 'earth' and 'graphia' meaning 'writing'.
Find out more about the earth.
Astronomers
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 sunlight.
Astronaut
A person who has been trained for travelling or living in in space.
★ Neil Armstrong was the first man to step on the surface, of the moon on 20 July 1969.
Meteoroids
The small pieces of celestial bodie which move around the sun are called meteoroids.
Shooting Stars
Sometimes meteoroids come near the earth and tend to drop upon it. During this process due to friction with the air they get heated up and burn with a flash of light. This phenomenon is called shooting stars.
Sometimes, a meteor without being completely burnt, falls on the earth and creates a hollow.
A galaxy
A huge system of billions of stars, and clouds of dust and gases is called a galaxy. The Milky Way galaxy or Akash Ganga is our galaxy.
Our Galaxy Milky Way or Akash Ganga
We see a whitish clusters broad band, like a white glowing path (way) of milk across the sky on a clear starry night. This whitish clusters band consists of millions of stars is the Milky Way galaxy.
In ancient India, it was imagined to be a river of light in the sky. Thus, it was named Akash Ganga.
Universe
The Universe is a cluster of millions of galaxies. A galaxy is a huge system of billions of stars, planet, clouds of dust and gases etc.
Our Universe
Our solar system is a part of our Milky Way galaxy with Millions of other solar systems. There are millions of such galaxies in the Universe.
Scientists are not certain about its size but we know that all of us you and I belong to this universe.
EXERCISES
1. Answer the following questions briefly.
(a) How does a planet differ from a star?
Ans.
(b) What is meant by the 'Solar System?
Ans. The sun, eight planets, satellites and some other celestial bodies known as comet, asteroids and meteoroids form the solar system. We often call it a solar family, with the sun as its Head.
(c) Name all the planets according to their distance from the sun.
Ans. The planets are as follows:
(The Sun) –> Mercury –> Venus –> Earth –> Mars –> Jupiter –> Saturn –> Uranus –> Neptune
(d) Why is the Earth called a unique planet?
Ans. 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.
(e) Why do we see only one side of the moon always?
Ans. The moon moves around the earth in about 27 days. Moon also rotates on its axis once in about 27 days. Since it takes exactly the same time (about 27days) to complete one rotation (spin) and one revolution (round). As a result, only same side of the moon is visible to us on the earth.
(f) What is the Universe?
Ans. The Universe is a cluster of millions of galaxies. A galaxy is a huge system of billions of stars, planet, clouds of dust and gases etc.
2. Tick the correct answer
A. The planet that is known as the "Earth's Twin" is:
1. Jupiter. 2. Saturn. 3. Venus
B. Which is the third nearest planet to the Sun?1. Venus. 2. Earth. 3. Mercury
C. All the planets move around the Sun in
1. Circular path
2. Rectangular path
3. Elongated path
D. The Pole Star indicates the direction to the
1. South. 2. North. 3. East
E. Asteroids are found between the Orbits of
1. Saturn and Jupiter
2. Mars and Jupiter
3. The Earth and Mars
Ans:
A –> (3) Venus
B –> (2) Earth
C –> (3) Elongated path
D –> (2) North
E –> (2) Mars and Jupiter
3. Fill in the Blanks.
1. A group of ________ forming various patterns is called a _________.
2. A huge system of stars is called _________.
3. _________ is the closest celestial body to our earth.
4. __________ is the third nearest planet to the sun.
Ans: Earth
5. Planets do not have their own __________ and ____________ .
Ans.
1. stars, constellations, 2. galaxy, 3. Moon, 4. Earth, 5. heat, light
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