WBBSE Class 6 Geography Solutions Chapter 1 The Universe and The Solar System

Detailed explanations in West Bengal Board Class 6 Geography Book Solutions Chapter 1 The Universe and The Solar System offer valuable context and analysis.

WBBSE Class 6 Geography Chapter 1 Question Answer – The Universe and The Solar System

Objective Type Questions :

Question 1.
In which unit the distances of universe are measured?
Answer:
Light year

Question 2.
What is the speed of light ?
Answer:
1,86,000 miles or 3,00,000 km per second

Question 3.
Which planet is known as ‘blue planet’?
Answer:
Earth

Question 4.
Which planet is known as ‘red planet’?
Answer:
Mars

Question 5.
Which is the brightest plaent?
Answer:
Venus

Question 6.
Which planet has the largest number of satellites?
Answer:
Jupiter

Question 7.
Which planet has only one satellite?
Answer:
Earth

Question 8.
Name the largest satellite of the Solar System.
Answer:
Titan

Question 9.
Name the planets between the Sun and the Earth.
Answer:
Mercury and Venus

Question 10.
What is the smallest planet in the Solar System?
Answer:
Mercury

Question 11.
Name the planet closest to the Sun.
Answer:
Mercury

Question 12.
Name the planet farthest from the Sun.
Answer:
Neptune

Question 13.
What is the position of the Earth from the Sun?
Answer:
Third

Question 14.
Name the first astronaut who landed on the Moon.
Answer:
Neil Armstrong

Question 15.
Which planet is known as Earth’s twin?
Answer:
Venus

Question 16.
How many planets are there in the Solar System ?
Answer:
Eight

Question 17.
Name the largest planet of the Solar System.
Answer:
Jupiter

Question 18.
How much time does a ray of sunlight take to reach the Earth?
Answer:
About 8 minutes

Question 19.
How much time does a ray of moonlight take to reach the Earth ?
Answer:
About one second

Question 20.
Which planets have no satellites?
Answer:
Mecury, Venus

Question 21.
Which planet has three rings round it?
Answer:
Saturn

Question 22.
What is the distance between the Sun and the Earth?
Answer:
150 million km

Question 23.
Which star is known as ‘Evening Star’ or ‘Morning Star’?
Answer:
Venus

Question 24.
What is the direction of rotation of Venus planet?
Answer:
From East to West

Question 25.
Name the two satellites of Mars.
Answer:
Deimos and Phobos

Question 26.
Name two Indian astronauts who went into space.
Answer:
Rakesh Sharma and Kalpana Chawla

Question 27.
How many satellites are there in Solar System?
Answer:
About 100

Question 28.
How many stars are there in our Galaxy ?
Answer:
About 1,00,000 million stars

Question 29.
Which is the centre of the Solar System – Sun or Earth ?
Answer:
Sun

Question 30.
State the significances of atmosphere.
Answer:
It acts as a Protective Blanket around the Earth

Question 31.
What is meant by Hydrosphere?
Answer:
The layer of water on the surface of the Earth is called the Hydrosphere.

Question 32.
What is the period of rotation of Moon?
Answer:
27 days 7 hours 43 minutes

Question 33.
Why is Mars an object of great interest amongst planets nowadays ?
Answer:
Due to possibility of life on it

Question 34.
What is the Red Spot?
Answer:
Red soil on the mars containing iron, silica, titanium.

Question 35.
Which planet is tilted at an angle of 98° ?
Answer:
Urenus

Question 36.
Name the planet whose polar caps show seasonal changes.
Answer:
Mars

Question 37.
With which planet do you associate the Great Red Spot?
Answer:
Jupiter

Question 38.
Name one gas found in the upper layer of the cloud of this planet.
Answer:
Ammonia and Methane

Question 39.
Which two planets are our closest celestial neighbours?
Answer:
Venus and Mars

Question 40.
The yellow face of the Sun is called-
Answer:
Photosphere

Question 41.
The outer layer of the Sun is called-
Answer:
Corona

Question 42.
The Sun moves faster at its equator than at its poles. At equator the rotation takes about-
Answer:
30 days

Question 43.
Light year is the unit of-
Answer:
Distance

Question 44.
Which planet is said to be cruel according to Indian astrology ?
Answer:
Saturn

Question 45.
Which planet shows the same face towards Sun ?
Answer:
Mercury

Question 46.
The Moon’s orbit is inclined to the Earth’s orbit at an angle of about-
Answer:
5 degree

Question 47.
From new Moon to full Moon, more and more of the Moon’s illuminated half faces the Earth and the Moon is said to be-
Answer:
Waxing

Question 48.
From full Moon to new Moon, less and less of the Moon’s illuminated half faces the Earth, so it is said to be-
Answer:
Waning

Question 49.
Which unmanned spacecraft landed on Mars in 1976 ?
Answer:
Viking-1

Question 50.
Which two poisonous gases are found on Jupiter ?
Answer:
Ammonia and Methane

Question 51.
Who discovered the Uranus planet?
Answer:
Sir William Herschel

Question 52.
What is the average temperature of the Earth?
Answer:
17°C

Question 53.
Planet is like a greenhouse.
Answer:
Venus

Question 54.
Planet spins on its axis from east to west.
Answer:
Venus

Question 55.
The planet which has the shortest day?
Answer:
Jupiter

Question 56.
The Halley’s Comet is seen from the earth after every-
Answer:
76 years

Question 57.
Name of the largest planetoid is-
Answer:
Ceres

Question 58.
Celestial body which radiats heat and light-
Answer:
Star

Question 59.
The planet having the longest orbit around the Sun is-
Answer:
Neptune

Question 60.
The natural science that deals with the study of celestial objects is-
Answer:
Astronomy

Question 61.
The theory that explains the expanse of the universe is-
Answer:
Big Bang Theory.

Define the following briefly : 2 mark each

Question 1.
What is an orbit ?
Answer:
Orbit is the fixed path along which the planets revolve round the Sun.

Question 2.
What are Sunspots ?
Answer:
The dark patches or black spots on the bright surface of the Sun are known as Sunspots.

Question 3.
What do you mean by Asteroids?
Answer:
Millions of tiny planets made of cosmic fragments found in the wide gap between the orbits of Mars and Jupiter are known as Asteroids.

Question 4.
What are Comets ?
Answer:
Comets are heavenly bodies, with a head and a tail, formed by condensation of small particles of gas and rock fragments.

Question 5.
What are Meteors ?
Answer:
Meteors are small fragments of metallic rock scattered in the Solar System. Meteors burn when they enter the Earth’s atmosphere and are called ‘Shooting Stars’.

Question 6.
What do you understand by “Meteorites”?
Answer:
The unconsumed parts of the Meteors which reach the earth’s surface are known as Meteorites.

Question 7.
What is universe ?
Answer:
Universe is a vast, infinite, heavenly space which comprises all the heavenly bodies, the Sun, the planets and several galaxies of stars.

Question 8.
What is a light year ?
Answer:
A light year is the distance which a ray of light would cover in a year’s time (About 9.5 Trillion kilometre).

Question 9.
What is Galaxy ?
Answer:
A Galaxy is a group of millions of shining stars scattered regularly in space. It is also known as the Milky Way or Akash Ganga.

Question 10.
What are the satellites?
Answer:
Satellites are small spherical bodies which revolve around a particular planet.

Question 11.
What is new Moon?
Answer:
When the Moon shows its dark side to the Earth.

Question 12.
What is full Moon ?
Answer:
When the Moon shows full face to the Earth.

Question 13.
What is Astronomy?
Answer:
It is the study of positions and motions of heavenly bodies.

Question 14.
What are shooting stars?
Answer:
When a meteor enters the Earth’s atmosphere, it burns and is called a shooting star.

Question 15.
What is cosmology ? known as cosmology.
Answer:
The study of Solar System is known as cosmology.

Identify the correct answers (MCQ) : 1 mark each

Question 1.
Which planet shows the same face towards the Sun
(a) Earth
(b) Neptune
(c) Venus
(d) Mercury
Answer:
(c) Venus

Question 2.
Which planet experiences all the season as of earth
(a) Saturn
(b) Uranus
(c) Mars
(d) Pluto
Answer:
(c) Mars

Question 3.
In Indian astrology, which one is cruel planet
(a) Mars
(b) Saturn
(c) Venus
(d) Uranus
Answer:
(b) Saturn

Question 4.
Which of the following is the cold planet
(a) Uranus
(b) Mars
(c) Venus
(d) Jupiter
Answer:
(d) Jupiter

Question 5.
Phobos and Demos are the satellite of
(a) Venus
(b) Neptune
(c) Mars
(d) Saturn
Answer:
(c) Mars

Question 6.
The age of the universe is about
(a) 10 billion
(b) 15 billion
(c) 20 billion
(d) 18 billion
Answer:
(b) 15 billion

Question 7.
The word nebula is Latin means
(a) rain
(b) clouds
(c) frost
(d) drizzle
Answer:
(b) clouds

Question 8.
The word planasthai in Greek means
(a) to return
(b) to come
(c) to wander
(d) to see
Answer:
(c) to wander

Question 9.
The word Solaris in Latin means
(a) Planet
(b) Sun
(c) Star
(d) Moon
Answer:
(b) Sun

Question 10.
Which planet experiences all the season as of earth
(a) Saturn
(b) Uranus
(c) Mars
(d) Jupiter
Answer:
(c) Mars

Question 11.
What position earth occupies in size from Sun
(a) 2nd
(b) 5 th
(c) 7 th
(d) 4 th
Answer:
(b) 5 th

Question 12.
Which two planets are nearly alike in size
(a) Neptune and Uranus
(b) Mercury and Venus
(c) Mars and Pluto
(d) Mercury and Mars
Answer:
(a) Neptune and Uranus

Question 13.
Which planets are called the ‘big four’?
(a) Jupiter, Saturn, Earth and Mars
(b) Jupiter, Uranus, Pluto and Earth
(c) Jupiter, Saturn, Uranus and Neptune
(d) Saturn, Uranus, Neptune and Earth
Answer:
(c) Jupiter, Saturn, Uranus and Neptune

Question 14.
Which two planets are called twin planets ?
(a) Venus and Earth
(b) Mercury and Venus
(c) Earth and Mars
(d) Pluto and Neptune
Answer:
(a) Venus and Earth

Question 15.
Halley’s Comet reappears after about
(a) 56 years
(b) 76 years
(c) 96 years
(d) 106 years
Answer:
(b) 76 years

Question 16.
Name the planet of which the orbit is very eccentric ?
(a) Neptune
(b) Pluto
(c) Uranus
(d) Saturn
Answer:
(b) Pluto

Fill in the blanks with correct words : 1 mark each

1. Heavenly bodies which radiates heat and light are called ____.
Answer:
Stars

2. The Earth is located at the _____ position from the Sun.
Answer:
Third

3. The Sun is about _____ million km. away from the Earth.
Answer:
150

4. Uranus completes one revolution in _____ years.
Answer:
84 years

5. The milky way is barred _____ shaped galaxy.
Answer:
Spiral

6 . _____ is called the ‘red planet’.
Answer:
Mars

7. The Moon has about _____ th the gravity of the Earth.
Answer:
1 / 6

8. The speed of the Moon’s revolution is about _____ km / hr.
Answer:
3,683

9. _____ was the first man to orbit around the Earth.
Answer:
Col. Yuri Gagarin

10. _____ became the first man to walk on the Moon.
Answer:
Neil Armstrong.

If the sentence is true, write ‘T’ and if false write ‘F’ against the followings : 1 mark each

1. Planets move around the Sun in circular orbits.
Answer: False

2. Satellites are smaller than the planets.
Answer: True

3. Saturn is the largest planet in the solar system.
Answer: False

4. The Moon reflects light from the Earth.
Answer: False

5. The Earth appears as a blue planet from space.
Answer: True

6. Rakesh Sharma was the first Indian to fly into space.
Answer: True

7. Kalpana Chawla was the first Indian woman in space.
Answer: True

8. Meteors are popularly known as ‘shooting stars’.
Answer: True

9. An asteroid is a tiny planet revolving around the Earth.
Answer: False

10. Uranus is the largest planet in the Solar System.
Answer: False

The Universe and The Solar System Class 6 WBBSE Notes

Earth : A unique planet. The Earth is a unique planet (Watery planet or Blue planet) because it is the only planet on which life exists.

The Universe : The science of Cosmology and Astronomy and solar system.

The Solar system : Solar system consists of the sun, planets, satellites, comets, asteroids and meteors. The Sun is the centre of the solar system. The sun is a vast hot gaseous mass. The distance between the Sun and the Earth is about 150 million kilometres. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune are eight planets. The gravitational force of the Sun keeps the planets in their orbits.

Life on Planets : The Earth is a unique planet because life exists only on this planet. Other planets have no atmospheres. There is a possibility of life on Mars.

Other Heavenly bodies : There are about 100 satellites revolving around different planets. The Earth has one satellite-Moon. Neil Armstrong, an American Astronaut was the first man to land on Moon on 21st July 1969. Comets are heavenly bodies with a head and a tail. Halley’s comet is visible on Earth after a period of 76 years.

Introduction :

A star-studded sky on a cloudless night is a facinating sight. It is very wonderful to watch the sky after the sunset. One would first see one or two bright dots shining in the sky. Soon you would notice the number of shining dots increasing. Then you cannot count them any more. The whole sky is filled with tiny shining objects – some of them are bright and others are dim. It seems as if the sky is studded with diamonds. That is why “Twinkle, twinkle, little star” is a significant line of a nursery rhyme. All objects that pertain in the sky are called celestial bodies. The Sun, the Moon and millions of shining objects in the sky are also celestial bodies. Sometimes celestial bodies are called heavenly bodies. Stars, planets, comets, meteors, meteorites, asteroids are all celestial bodies. The stars in this infinite space or sky cling together in groups. Each large group is called the galaxy.

The Universe :

Definition : The Universe can be defined as everything that exists, everything that has existed, and everything that will exist. The Universe is all of space and time (space time) and its contents, which includes planets, moons, minor planets, stars, galaxies, the contents of intergalactic space and all matter and energy. The size of the entire Universe is still unknown.

Etymology : The word ‘Universe’ derives from the Old French word ‘univers’, which in turn derives from the Latin word ‘Universum’. The latin word was used by Cicero and later Latin authors in many of the same senses as the modern English word is used.

How vast is the Universe? : The Universe is indeed very vast in size and infinite space having millions of galaxies and heavenly bodies. The vastness of the Universe cannot be easily imagined, in view of great distances involved. Distances between heavenly bodies cannot be expressed in units like kilometre or mile which are used for measuring this Universe. A light year is the unit adopted for measuring distances in the Universe. The Star nearest to the Sun is Proxima Centauri. It takes about four years for light to travel the distance between Proxima Centauri and the Earth. Then it is very difficult to imagine how big the Universe is ! Scientists are still trying to find out more and more and more about it. We are not certain about its size, but we know that all of us-you, I belong to this Universe.

How did the Universe originate?

The Universe consists of all things that exist planets, stars and galaxies. The origin of this Universe has its root in the “Big Bang Theory”, Most astronomers beliese that the Univetse came into existerce about 15 billion years ago in a gigantic explosion celled the Bia Bang. Acconding to this theory, about 15 billici years ago all of the matter and energy of space wes concentrated at one point. Thus there was a tremendous explosion.

This explosion is lanown as the Big Beng in present drys. Small atoms formed within mirnutes of the explosion and the process of creation was started. All of the matter and energy, even the space itself, which were compressed into an infinitely small volume, then began to expand at an incredible rate. Within two to three minute, the whole thing that grown to the size of the solar system. In course of time it cooled enough to form Hydrogen and small amount of Helium gas. The Bia Beng modet states that the exrliest state of the Universe was extremely hot and dense and that it suberquently expanded.

The initial hot, dense state is celled the Planck epoch, a brief period extending from time seto to one planck time unit. During the Planck epoch, all types of matter and all types of energy were concentrated into a dense state, where gravitation is belisved to have been er strong es the other fundamental foroes, and all the forces may have been unified. During the bilions of years that followed, immense heat and huge energy together with the gases and coemic clouds fomed the so called Universe. The golaxy was created by this Big Bang process and from them the sters, the planets and other cosmic objects wete formed or we see it today. The expansion of unikerse is still continuing.

Age of this Universe : The gigantic explosion is called the “Big Bang” which cccured 15 billion years ago. The age of the Univetse is thus considered about 15 billion years starting from the Big Bang episode. The current estimate of the age of the Universe is about 13 billion years.

The Celestial Bodies  :
Definition : All objects that belongs to the sky are called celestial bodies. The Sun, the Moon and millions of shining objects in the clear night sky are also celestial bodies. Sometimes celestial bodies are called heavenly bodies. Stars, planets, comets, meteors, meteorites, asteroids are all celestial bodies. Some celestial bodies have their own heat and light and are called stars. Some heavenly bodies do not have their own heat and light. They receive the light from the stars. These are called planets, clusters of millions of stars in the Universe are called Galaxies.

Galaxy :
Definition : A large group of stars, dust and light gases bound together by their own gravity is called a galaxy. It is a flattened system of different shapes and sizes. Several galaxies make up the Universe. There are 10″ galaxies in the Universe. Our Solar System is a part of the Universe which consists of clusters of millions of stars. These are called galaxies.
Earth’s Galaxy : Earth’s galaxy is called the Milky Way or Akash Ganga. The Milky way is a large spiral-shaped galaxy. It spans about 100,000 light years across and is about 10,000 light years thick at the centre.

Why its name Milky Way?

Earth’s Galaxy is called the Milky Way because it appears as a soft glowing light of billions of stars so far away that they cannot be seen individually. With his telescope, Galileo discovered this band of light was produced by countless individual stars which the naked eye cannot resolve.

Nebula :
Terminology : The word ‘nebula’ is derived from the Latin word for ‘Clouds’.
Definition : A nebula is the cloudy luminous patch of gas (cosmic cloud), made up of dust, hydrogen, helium gas, whirling around the centre of an eddy in the space. More than one nebula is called nebulae.
Formation : Scientists think the Nebulae are the hot gaseous form of matter. When the Nabulae cool, the stars are born.

Hubble, Wyse and Mayall have found new facts about the nebulae after making special studies.
Types : The Nabulae belong to two types-(i) Galactic Nebulae and (ii) Extra Galactic Nebulae.

(i) Galactic Nebulae : These nebulae exist within our Milky Way. Their sizes are thousands times larger than our solar system.
(ii) Extra-galactic Nabulae: These nebulae are situated away from our Milky Way. They have a definite and similar shape. Some are spiral nebulae.

How the Sun, the solar system were formed?

About 4.6 billion years ago the Solar System was just a spinning disc of dust and gas. These gases, mainly hydrogen and partly helium, together with dust in space created a cosmic cloud. This cloud then got disturbed by various cosmic factors and thus squeezed. Gradual cooling caused gradual contraction in the size.

The disc gradually formed a nebula called solar nebula. The more the size of the nebula continued to decrease, the more the velocity of rotatory motion continued to increase. Thus, the nebula started spinning at a faster speed and consequently centrifugal force became so great that it exceeded the centripetal force. The outer layer of the disc, the matters became thinner and fragmented. The particles, either began to stick together or collided with others to form clumps. They began to revolve around the centre of the so called concentrated mass (new born Sun) due to its central gravitational pull.

The central part of the nebula which remained behind became the Sun and originate nine rings and thus nine planets have been formed. Some rings also separated from the gaseous mass of the planets and revolved round them as sub-planets. The remaining part of the original gaseous mass became the Sun. These planets and sub-planets along with the Sun are known as Solar System or Solar Family. However, in our own Solar System the members may be grouped into the following six categories :

• Stars
• Planets
• Satellites
• Comets
• Meteores
• Asteroids.

Stars :

Definition : Some celestial bodies in the Universe are very huge and hot. They are made up of various gases. They have their own heat and light, which they emit in large amounts. These celestial bodies are called stars. The Sun is also a star. The Sun is the nearest star to the Earth. It is about 14.70 crore kilometre away from the Earth. The light of the Sun takes eight minute and twenty second to reach the earth.

Physical Properties : Stars are self luminous bodies. It means they have their own heat and light. Stars are made up of hot gases giving out flames. They are usually very big in size but they are very far away from our earth. That is why they look very small. There are millions of stars in this limitless sky.

Why stars seems twinkling to us ?
The light from the stars passes through different layers of the atmosphere with varying densities. As a result, stars seem twinkling to us.

Second nearest star : Next to the Sun, the second nearest star is the Proxima Centauri or Alpha Centauri. It lies at a distance of about 4.25 light years from the earth. It was discovered in 1913. The mass of this star is 0.1 times than that of the Sun.

Sources of heat and light : Stars are intensely hot, glowing masses which produce massive energy. Hydrogen is the primary elements of building block of stars. The main source of the heat of a star is due to the conversion of Hydrogen gas into Helium gas. This heat is the primary source of self-illumination or shining of the stars.

Number of visible stars : There are 10²² stars in the Universe. It has been estimated that about 8000 stars visible from the Earth by the naked eye. Out of this, 4000 stars are visible in the Northern Hemisphere and 4000 in the Southern Hemisphere. In either hemisphere, 2000 stars are visible at any given time. The other 2000 stars are located in the day time sky and are not visible due to the brightness of the Sun.
Constellations : While watching the clear night sky, you may notice various

patterns formed by different groups of stars. These are called constellations. These constellations were named in honour of mythological characters. They hardly bear resemblence to names they are given. Today, 88 constellations are recognised.

Ursa Major or Great Bear is visible throughout the year in the northern sky in most of the Northern Hemisphere. The seven brightest stars of Ursa Major form a pattern known as the Big-Dipper in USA, the Plough in U.K. and Saptarshi in India. It’s name means ‘the great bear’. Orion, the hunter, is one of the most beautiful of all constellations. It is seen in the south-southwestern sky. In Bengal it is known as Kalpurush.

The Sun :
Definition : The Sun is a medium size star situated at the centre of a huge rotating solar system consisting of nine planets (now eight planets except Pluto), their satellites and numerous small bodies known as asteroids. Its gravitational pull holds the other members in orbit and governs their motion.

Shape, size and colour : The shape of the Sun is perfectly spherical or round. Although it is slightly less than average sized star. Like all stars it is a ball of hot glowing gaseous body in the sky. The Sun is 13 lakh times bigger than our earth. It has a radius of about 700,000 km. The Sun is gaseous and not solid like the Earth. It looks big and bright because it is comparatively nearer to us or Earth. It is yellowish in colour and is of medium shape and size among the stars. Astronomers describe it as ‘a yellow dwarf’.

Weight and Volume : Though Sun is made up of hot gases i.e., very light substances it will still weight over 750 times more than all the planets put together. In volume Sun is so big that a million earths would fit into it. It is 1.3 billion (1 billion = 1000000000) times the volume of the Earth.

Temperature : We get heat and light from the Sun. The surface temperature of the Sun is about 6000° C. In the core of the Sun, the temperatue is estimated to be about 20,000,000°C. Such extremely high temperatures are produced by the conversion of hydrogen into helium by the process of fusion. Heat is generated by this process and the Sun radiates energy in the form of electro-magnetic radiation. Solar prominences rise like huge flames hundreds of kilometer from the Sun’s surface.

Time takes for light : The Sun is about 150 million (1 million = 10,00000) km away from the Earth. Light, which travels at the speed of 3,00,000 km per second, takes about 8.5 minutes to reach the Earth from the Sun.

Layers of the Sun : From centre to the surface of the Sun, there are four distinctive layers; they are-

(a) Core : Interior core of the Sun, consist of hydrogen and helium gases with a temperature is called Solar core. The temperature at the core or centre of the Sun is around 1.4 million °C.

(b) Photosphere: The visible yellow face around the core of the Sun is called the photosphere or the sphere of light where, the temperature is about 6000° C. The rays and heat radiate from it.

(c) Chromosphere : Surrounding the photosphere is Chromosphere (temperature 32,400°C) which is pink or reddish in colour. The flames of the chromosphere go up thousands of kilometre and are called Prominences.

(d) Corona : It is the uppermost layer of the Sun. It is visible to unaided eyes only during solar eclipses. Temperature of the Corona is about 2,700,000° C, hot enough to emit X-rays.
Density of Gas : The density of the gas in each layer decreases with the increasing altitude, just as the earth’s atmosphere thins with height. The corona, accordingly, is the least dense of the Sun’s layer.

Planets :
Definition : Some celestial bodies are made up of solid material. Since they not made of burning gases they do not have heat and light of their own. They only reflect the light which they receive from a star. Such celestial bodies are called planets. The Sun is a star and our Earth is also a planet which receives its light and heat from the Sun (star).

Etymology : The word ‘planet’ comes from the Greek word ‘planetai’ which means ‘wanderers’ as they seemed to move about or wander in the sky. All planets are revolving around the Sun in their respective elliptical orbits. Time taken for a complete revolution in each case is fixed.
Revolution speed of planets : All planets revolve the Sun in ellipse-like orbits. Their average speed including Pluto is 22.7 km per second. The planets closer to the Sun move faster than those which are more distant from it.

A Rotation of planets : Each planet rotates at different speed about their respective axis. All except Venus rotates in an anti-clockwise direction. It is really surprising that Venus rotates in a clockwise direction. To every one’s astonishment Venus sees the Sun rising in the West.

Smallest and closest planet : Mercury is the smallest planet in the Solar System and closest planet to the Sun.

• A Earth’s position : In terms of distant from the Sun, the Earth’s position is third.
• Largest planet : Jupiter is the largest planet in the solar system.
• Brightest planet : Venus is the brightest planet in the solar system.
• Number of planets : Our solar system is made up of eight planets. In order of their distance from the Sun, these are : Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

An easy way to memorise the name of the planets in order of their distance from the Sun is :
“My Very Efficient Mother Just Served Us Nuts”

Classification of planets : Almost all the planets fall into two groups :

(a) Inner planets : Mercury, Venus, Mars and Earth are called the Inner planets. They are also known as terrestrial (earth like) planets.
(b) Outer planets : These lie beyond the orbit of Mars, Jupiter, Saturn, Uranus and Neptune are the Outer planets.

There is another way of grouping the planets-
(a) Inferior planets : Mercury and Venus are called inferior planets because they lie closer to the Sun than the Earth.
(b) Superior planets: All the planets which have their orbits outside the Earth’s orbit are called superior planets.

Comparison of Stars and Planets :

Stars	Planets
1. A star is made up of hot, burning gases.	1. Planets are made up of solid material like rocks and stones.
2. Stars emit light of their own.	2. They shine because of the light they reflect from the Sun.
3. Stars twinkle.	3. Planets do not twinkle.
4. Stars are very big.	4. Planets are very small as compared to the stars.
5. Stars are very hot.	5. Temperature of planets depends on its distance from the Sun.
6. There are millions of stars.	6. There are nine planets.
7. The Sun is an exmaple of a star.	7. The Earth revolves around the Sun. It is an example of a planet.

The brief description of the planets of our Solar System is given below :

Inner Planets:

1. Mercury: The Innermost planet : Mercury is the nearest planet to the Sun and smallest planet in the solar system. It is named after the messenger of the Roman Gods.

• Distanc: Its distance is about 58 million km.
• Diameter : Its diameter is 4878 km.
• Max. and Min.

Temperature :
The maximum temperature of this planet is 430°C and minimum temperature at opposite side is – 180°C.

• Rotational Period : 58 days.
• Length of day : 58 days, 15 hrs 30 minutes
• Length of year : 87.97 days.
• Satellite : None.
• Revolutionary Speed : It is the swiftest planet and completes one revolution in 88 days.

Venus : The veiled planet : Venus is named after the Roman Goddess of love and beauty.

• Distance from Sun : It is the second planet from the Sun and lies 107 million km distance from the Sun.
• Size : It is like the Earth in size and mass and hence also known as the “Earth’s twin”.
• Diameter : 12104 km.
• Average surface temperature : It is the hottest planet in the Solar System and its average surface temperature is 450°C. It is the warmest planet.
• Orbital period : 225 days.
• Length of day : 243 days, 14 minutes.
• Direction of rotation : It spins clockwise, opposite to that of Earth.

Earth : The Blue Planet : It is the largest of the inner planets. It is the fifth largest planet in the solar system and third in distance from the Sun. The Earth is known as the “Watery planet” or the “Blue planet”. It is the only known planet which has life on it.

• Distance from the Sun : 150 million km.
• Average surface temperature of the Earth : 15°C or + 14°C
• Length of day : 23 hrs, 56 minutes, 4 seconds.
• Length of year : 364 days, 48 minutes, 46 seconds approximately 365.25 days.
• Average speed of Revolution : 29 km. per second and direction of the revolution is anti-clockwise.
• Satellite : One (moon).

Earth : The Blue, Watery Planet The “full Earth” was an unknown spectacle before the Apollo space flights. Such photographs of the Earthhave vastly increased our knowledge of weather patterns and climate. The Earth is called a waterly planet because 70% of its surface is covered with water. The Earth reflects about one third of the light that falls on it. The Earth’s atmosphere scatters the light and creates a predominantly blue planet.

Mars : The Red Planet :
Mars is named after the Roman God of war. Its iron-rich red soil and pink sky give it the name ‘Red planet’. ‘

• Distance from the sun : 228 million km (1.5 times that of Earth).
• Average surface temperature: -25° C,
• Length of day : 24 hours, 37 minutes,
• Length of year : 1 year and 321.73 days.
• Satellites : 2 (Phobos and Deimos).
• Size : Small (diameter less and 25km).
• Discovered : In 1877.

Jupiter : The Giant Planet : Venus is named after the Roman Goddess of love and beauty. It is the largest planet of the Solar System. About 1300 Earthsized balls could fit within this enormous planet.

Jupiter rotates faster than any other planet. This fast spin causes high winds. D

• Average surface temperature : 150° C.
• Length of day : 9 hours, 50 minutes.
• Length of year : 11 ye ars and 315 days.
• Distance from the sun : 778 million km.
• Satellites : 63
• Size : Diameter ranges from 3000 km to 5000 km.
• Discovered : In 1610 by Galileo Galilei.

Saturn : The Jewel Planet : Saturn is named after Jupiter’s father in Roman mythology. It is the second largest planet and the most beautiful planet in the solar mainly because of its spectacular rings. Which are made up of ice and icecovered-dust particles. The other giant planets also have rings, but the saturn’s rings are brighest and most complex.

• Average surface temperature: -178°C
• Length of Day : 10 hours, 41 minutes..
• Length of year : 29 years and 167.25 days.
• Distance from the Sun : 1,400 million km (9.6 times that of Earth)
• Satellites : 18 known (22 or more expected).
• Discovered : Between 1655 and 1684.

Uranus : A Planet on its side : Uranus is named after the Roman God of the sky. This planet is about 4 times the size of Earth. Its axis is fitted at 98°. Unlike the other planets that spin like tops as they circle the Sun. Uranus seems to be rolling along its orbit. It completes one revolution in 84 years. This planet appears greenish in colour because the methane gas present absorb the reddish colour from the sunlight.

• Average surface temperature: -213° C.
• Length of day : 16 hours, 48 minutes. It spins on its side, clockwise, opposite to that of Earth.
• Length of year : 84 years and 3.65 days.
• Distance from the Sun : 2870 million km.
• Satellites: 15.
• Discovered : Between 1787 and 1948.

Neptune : The Last Giant : Neptune is named after the Roman God of the sea, the son of Saturn and brother of Jupiter. Neptune is very similar to Uranus and can be considered its twin.

1. Average surface temperature: -214° C
2. Length of day : 16 hours, 3 minutes.
3. Length of year : 164 years and 288.54 days.
4. Distance from the sun : 4,500 million km.
5. Satellites : 8.
6. Discovered : Between 1787 and 1948.

Pluto : The Dwarf Planet : Once it considered to be the ninth planet in the Solar System. Pluto’s orbit is unusual. It is highly elongated and tilted at an angle of 17° as compared to the orbits of the rest of the planets and for these causes Pluto was declared to be a ‘Dwarf Planet’ by the astronomers in 2006. According to them, dwarf planets cannot repel a celestial body that intrudes into its orbit and it is another cause for termed as dwarf planet Pluto, even smaller than the Moon, completes one revolution in 248 years. It has one satellite, named Charon (son of Pluto). Pluto was discovered in 1978.

Comparative Details of planets

Negative values of rotation period indicate that the planet rotates in opposite direction to that it revolves round the Sun.

Satellites :

Definition: The celestial bodies which rotate on their own axes and revolve round the planets are called satellites. The satellites revolve around the planets in the same way as the planets revolve around the Sun. Satellites shine by reflecting light from the Sun. These natural satellies are frequently referred as ‘Moon’ Humanmode satellite: They are artificial bodies. They are designed by scientists to gather information about universe.

Word Origin : The word satellite has its root in the Latin ‘Satelles’, which means ‘attendant’. The word ‘satellite’ means a follower and they follow the planets in their paths around the Sun. Planets and their satellites: Satellites are opaque bodies like the planets shining by reflected sunlight falling on them. All planet’s do not have satellites. As a result of recent space exploration the number of known satellites has increased. Saturn has the largest number of satellites, namely 20. It is now known that there are at least 57 satellites in the Solar System. Four satellites Ganymede and Callisto of Jupiter, Titan of Saturn and Triton of Naptune are larger than Mercury, the smallest planet. Most of the satellites are too small to hold an atmosphere around them. Titan, the largest satellite of saturn has an atmosphere around it.

The Moon :

Moon, the only natural satellite of the Earth, is our nearest heavenly body being only 3,85,000 ~km away from the Earth. It is about 50 times smaller than the Earth.

The diameter of the moon is about one-fourth the Earth’s diameter. The day temperature may be as high as 127° C and the temperature may drop down to -173° C just before the lunar dawn. Due to lack of atmosphere there is no weather, no clouds, no rain, no wind and no water on its surface.

The moon moves around the earth on an elliptical orbit at an average speed of about 3700 ~km per hour. It completes one revolution around the earth in 27 days. The time taken to complete one rotation in about 29 days.

Since moon takes almost the same time to rotate on its axis and complete one revolution, the same side of the Moon always faces the Earth. The Moon has about 1 / 6 th the gravity of the Earth. So if you weighted 100 kg on Earth you would weigh 16.6 kg on the Moon.

Phases of the Moon : The Moon’s
appearance changes
as it moves around the Earth. These changing shapes, or the changes in the Moon’s visible shape are known as the phases of the Moon.

1. New Moon : When the moon is between the Earth and the Sun, the part of the Moon facing the Earth is in complete darkness. This position is called the New Moon
2. Waxing Crescent: Three days after the New Moon, a thin illuminated surface of the Moon is visible from the Earth.
3. First Quarter: On the 7th day after the New Moon, the Moon looks like a luminous halfcircle.
4. Waxing Gibbous : On the 10 day after the New Moon, more than half, but less than full portion of the Moon is lighted.
5. Full Moon : On the 14th day after the New Moon, the Moon shows its full lighted surface. This face is the Full Moon.
6. Waning Gibbous : The 17th day after the New Moon is waning gibbous.
7. Last Quarter : On the 21st day after the New Moon, again the Moon looks like a luminous half circle. This phase is the Last Quarter.
8. Waning Crescent: On the 28th day after the first New Moon, once again the New Moon occurs. This circle is repeated every month. The period of time from one Full Moon or New Moon to the immediate next one is called a Lunar Month.

Eclipse : An eclipse is the darkening of a heavenly body when the shadow of one object in space falls on another object.

1. Lunar Eclipse : A lunar eclipse occurs when the earth (small object) is between the Sun (large light source) and the Moon, i.e., the Sun, Earth and Moon are in a straight line with the Earth in between the Sun and the Moon. The shadow of the Earth falls on the Moon.
2. Solar Eclipse : A solar eclipse occurs when the Sun Earth and Moon are in a straight line with the Moon positioned in between the Sun and the Earth. The shadow of the Moon is cast on the Earth.

Other Members of the Solar Family –

1. Asteroids : Definition : Thousands of small planetary bodies which revolve around the sun in big gap of about 550 million km. between the orbits of Mars and Jupiter are called asteroids. Asteroids are also called Planetoids or minor planets. Facts about Asteroids : They are rocky objects. This has come to be called the asteroid belt. So far more than 5000 asteroids have been identified and catalogued. They are irregular in shaped. Regardless of size and shape, all asteroids rotate on their axes every 5 to 20 hours. Mean period of their revolution is 4.5 years. The largest or biggest of the asteroids in Ceres, has a diameter of about 1000 km.

Meteors and Meteorites :

Definition : When asteroids collide with one another, fragments of rock may break off. These pieces may find their way towards the Earth.

Such objects are called meteors. Meteors are popularly known as ‘shooting stars’. Meteors are usually small and burn up before they can reach the earth’s surface. When meteors are large and do not burn up completely, they land on the earth’s surface and are known as meteorites. Sometimes a large meteorite strikes earth and make large holes, called Craters. Such a meteorite struck Siberia in Russia in 1908 . The most famous site is the Meteor Crater in Arizona of USA. The Crater is 1.2 km across and 170 metre deep.

Comets : Visitors of the Solar System –

Definition : Comets are bright objects with an elongated tail which have curved orbits around the Sun. As they have long orbits they appear at long intervals. Comets are heavenly bodies with a head and a tail. Word Origin : The word comet comes from the Latin word ‘Stella Cometa’ meaning ‘hairy star’.

Orbit and movement : Comets move around the Sun in irregular orbits but their orbits are such elongated ellipse that it takes them hundreds and sometimes even thousands of years. Comets have been compared to large dirty snowballs.

The comet becomes visible only when it travels close to the sun. Example: The most famous comet is Halley’s Comet. Its orbital period averages 76 years. It was seen in 1910 and last sighted in 1986 . It is due to return in 2061 or 2062.

What is coma? A comet is characterised by a long, luminous tail. But this is visible only when the comet’s orbit passes close to the Sun. When the comet travels close to the Sun, the ice melts to a head of gas called coma.

Space Venture or Journey to Sapce

During the years since world war II, a new science of space technology and astronautics has developed and the first successful man made earth satellite was Sputnik-I, launched by Russia on october 4, 1957.

For centuries man had hoped that one day he would set foot on the Moon. On 4th October, 1957, the Soviet spaceship Sputnik-1 had gone beyond the force of gravitation and moved round the Earth for 56 minutes at a height of 900 ~km. In the same year Russia had sent another spaceship, Sputnik-II, with a passenger dog named Laika. But unfortunately Sputnik-II was destroged in the space.

Advancement of Space and Moon Exploration –

1. Space exploration began with the launching of Russia’s Sputnik-1 into space on October 4, 1957.
2. Sputnik-2 followed a month later and carried with it a dog ‘Laika’.
3. The USA entered the space arena on January 31, 1958 with the launching of the Explorer-1.
4. In October 1959, the Russian satellite Luna- 3 sent pictures of the far side of the moon.
5. In 1959 Russian scientists had launched manless Lunik-1 and Lunik-2 directly towards the moon.

But Lunik-2 dashed against the Moon and was broken. At the end of the year Lunik-3 was launched successfully and it began to move around the Moon and televised the picture of the Moon’s opposite side.

6. First honours for space flight went to Russian Air Force Major Yuri Gagarin in 1961.
7. The first women cosmonaut, Valentina Tereshkova of Russia (now CIS) flew into space in June 1963 and stayed for about 3 days in the orbit.
8. Later Russian moon-ship Lunik-9 alighted in the Moon and had sending pictures to the Earth.
9. In 1966 and 1967 American Scientists had sent several spaceships with men and they came back with resourceful information about the Moon.
10. The man stepped on to the surface of the Moon for the first time on July 21,1969 at 8.26 a.m. as per Indian standard time. The rocket named Saturn was launched from the Cape Kennedy Space Centre at Florida, USA on July 16, 1969. A giant spacecraft, Appollo-II was fitted atop the Saturn. The Apollo-II carried Eagle, the lunar landing craft.

Three astronauts, named Neil Armstrong, Michael Collins and Edwin Aldrin Jr. got into ApolloII. As the craft came near the Moon, the astronauts prepared to land. Michael Collins stayed in the spacecraft while the other two entered the lunar module Eagle. When everything was ready, the Eagle separated from space-craft and headed towards the Moon. As it reached the Sea of Tranquility – a vast dry plain or maria, the lunar module landed on its spidery legs. Then, the hatch of the Eagle was opened and Neil Armstrong stepped on to the Moon.

Just after landing on the Moon Armstrong remarked with joy, ‘That’s one small step for a man, one giant leap for mankind’. After 30 minutes Aldrin came down from the Eagle to become the second man on the Moon.

Other Explorations

USSR sent up the unmanned Luna-16 (September 12, 1970) and Luna-17 (November 19, 1970). Luna-16 picked up Moon Soil samples and returned to the earth on September 24, 1970.

India’s Space Research

ISRO (Indian Space Research Organization)the government institution that conducts and supervises space research in India. India’s first artificial satellite was Aryabhatta. Bhaskara-1, Bhaskara-2, INSAT, etc. are a few others satellites. The first Indian to travel successfully to space was Rakesh Sharma in 1984. The first Indian lunar vehicle from earth to land successfully on the moon was Chandrayana (2008).

India’s first Moon exploration by Chandrayaan-1 carried four Indian payloads and six foreign made science instruments, including the Moon Minerology Mapper (M₃) which first detected water molecules on the surface of the Moon. ISRO’s (Indian Space Research Organisation’s) Chandrayaan-1 spacecraft, launched in October 2008. had experienced instrument failures earlier this year, leading to loss of communication with the spacecraft and prompting the agency to end the lunar mission in August.

Notable Indian Astronauts :

Kalpana Chawla : She was the first Indian-American astronaut and was the first Indian woman in 1997.

She went into space as a mission specialist on space shuttle Columbia in 1997 and spent about 372 hours in space. Her second space mission was on January 16, 2003. On February 1, 2003,

her space shuttle columbia met with a disaster during re-entry into the earth’s atmosphere and along with all the seven crew members Kalpana Chawla died.

Rakesh Sharma : He was the first Indian to fly into space aboard Soyuz T-II on 2nd April, 1984. He spent eight days in space in the Salyut-7 space station.

Sunita Williams : She was an American astronaut of Indian origin holds the record for the longest single space flight by a woman for about 195 days. She is accredited with a record 50 hours 40 minutes of most space walk time for a woman.

Do you know?

Question 1.
What is sky?
Answer:
The space above the earth that you can see when you look up, where clouds and the Sun, Moon and Stars appear. The sky is limitless. The sky is bright blue in colour, like the sky in a clear day.

Question 2.
What is a light year?
Answer:
A light year is the unit adopted for measuring distances in the Universe. A ray of light travels at a speed of 300,000 km per second. A light year is the distance which a ray of light would cover in a year’s time. This works out to 9.5 million million kilometre.

Question 3.
What is epoch?
Answer:
A length of time, which is a division of a period.

Question 4.
Origin of the word Solar:
Answer:
The word ‘Solar’ comes from the Latin word ‘Solaris’ meaning ‘Sun’.

Question 5.
Some well-known Constellations :
Answer:
Some well-known Constellations with their Indian names are given below :

1. Ursa major (Great Bear)-Saptarishi
2. Ursa minor (Little Bear)-Dhruva Matsya
3. Orion (Hunter)Mirga
4. Draco (Dragon)Kaleya
5. Scorpio-Vrishchika.

Question 6.
Orbit
Answer:
All the eight planets of the Solar System revolve around the Sun in fixed paths. These paths are elongated. They are called orbits.

Question 7.
Why is venus hotter than Mercury (nearest planet to the Sun), even though venus is further away (second nearest to the Sun) from the Sun?
Answer:
It is all for the atmosphere that venus has. The intense heat is the result of accumulation of CO₂ (carbon dioxide) and SO₂ (sulfur dioxide) gas in the atmosphere of this planet. Radiation from the Sun is absorbed by the plaent (venus) and the heat emitted is trapped by the CO₂ in venus’s atmosphere which creates increase of heat extensively. The atmosphere of the venus is made up of mostly carbon dioxide which traps the heat of the Sun, making the surface temperature as high as 450° C.

Question 8.
Why is Venus called veiled planet ?
Answer:
Venus is surrounded by a thick cloud cover hence known as the ‘veiled planet’.

Question 9.
Why is Venus known as ‘evening star’ and ‘morning star’?
Answer:
Venus is the first to be seen in western night sky. It is never seen throughout the night. It rises before dawn and sets at sunset. These happen due to clockwise rotation of venus.