6.Chapter1.Geo.Planet Earth and the Solar System

Chapter 1.Geography.

Planet Earth and the Solar System

We can see countless glittering tiny objects in the sky at night.  Most of these appear twinkling They are stars.  The other glittering objects which do not seem to be twinkling may be planets.  During the day, we see the Sun, which is also a star all the objects in the sky, which appear similar to us, are the heavenly bodies.  The sun, the stars, the moon, the planets and other objects are all heavenly or celestial bodies.  You would be surprised to know that even our earth, on which we live, is a celestial body.  Foida fas.  The stars and the planets, which we see in the sky, are very small part of the vast 'Space', which is limitless.  There are billions of celestial bodies spread over the vast space.  They are very, very far away from us.  Hence, we cannot see all of them.  The vast limitless space which includes all celestial bodies is called Universe.  GALAXIES Though there are billions of celestial bodies spread in the vast universe, they are not uniformly distributed in the space.  The countless stars in the space form huge clusters.  One cluster may contain billions of stars.  All the stars in a cluster are held together by mutual gravitational force.  Such a huge cluster of billions of stars, along with the giant collection of gas and dust, is called a Galaxy.

Page 2 Our earth, along with the other planets, forms the Solar System.  The Do You Know?  Solar System is located in the outward spiral (Orion Arm) of the Milky Way Milky Way Galaxy, a faint white band, stretching Galaxy (Akash Ganga).  Most likely, there across the sky, is a barred spiral galaxy.  It contains a billions of other solar systems in bar across its center region and has two major arms.  The Orion Arm is located between two major arms.  our galaxy and billions of galaxies in the universe.  As we know, there are different types of celestial bodies in the universe.  Let us learn more about some of them STARS gasta Stars are self - luminous heavenly bodies.  They are made up of hot gases.  They generate heat and light and radiate it in the space.  The number of stars is countless) we cannot see all of them at a time.  It has been said that, at one time, we can see not more than 6,000 stars.  Though, stars are very huge bodies, they look very small as they are very far away from the earth.  The distance between celestial bodies is usually measured in a unit known as light year.  Some stars are so far away that the light radiated by them reaches us in millions of years.  The nearest star to the earth, other than the sun, is the 'Proxima Centauri'.  It is about 4% light years away from us.  Do you know?  Disturbance in the atmosphere causes star light to bend slightly.  As a result, some of the light reaches us directly and some gets slightly bent away.  This makes a star to twinkle.  • Light travels at a speed of about 3 lakh km per second the distance covered by a ray of light in a year or 365 days is called a light year.  ) 

CONSTELLATIONS If you observe the stars in the clear night sky, they appear to form different shapes and patterns and move from west to east.  The formations may resemble animals, humans or any other object.  The groups of stars which are recognized by their formations are called Constellations.  

Ursa Major, also called the Great Bear, is a constellation of several stars.  It appears in the northern sky.  In India, the seven stars called Saptarishi Mandal, is a part of Great Bear.  There are several other 

Page 3formations of stars, which have been given names by the astronomers.  The Polan's two brightest stars at the head of the Saptarishi Mandal, called Pointers, point towards the stationary star called Pole Star or Dhruv Tara in the northern sky.  Pole Star lies above the North Pole.  It always indicates the North direction Indians and Greeks have been studying the shapes and patterns of stars since ancient times.  In modern constellation times, the space scientists and astronomers use powerful and large - sized telescopes to study the celestial bodies.  The SOLAR system the sun and its companion celestial bodies constitute the solar system.  The eight planets, their Tutagatharam companion satellites, asteroids, meteors and comēts are the members of the solar system.  They all revolve around the sun on their fixed paths called Orbits.  The Evolution of the Solar System A question sometimes arises in our minds, how were the sun and its companions born?  Some scientists believe that a giant cloud of gases and dust, called the Nebula, appeared moving in the space about 4.6 billions of years ago.  It cooled and gained very fast rotation.  The eight balls of gases of different sizes were separated from the Nebula.  The remaining central mass of the Nebula changed into a star known as the Sun.  The other eight balls changed into planets, It is believed that the satellites were formed when small balls of gases separated from the central mass and were attracted by their companion planets.  They began Nebula forming planets to revolve around their planets

.Page 4 Do you know?  The word 'planet' is derived from the Greek word planas thai which means 'wanderer The word' satellite 'is derived from the Latin word satellite which means an attendant'.  The word 'solar' is derived from a Latin word solaris which means sun.  THE SUN GURUTWA The Sun is a star.  A star does not have a solid surface, but is a ball of gases held together by its own gravity.  It generates heat and light and radiates them into space.  The Sun does not have any rings.  It is the center of our solar system.  Life would not be possible on earth without the sun's intense energy The Sun is a very huge mass, much bigger than all its companions put together.  It is about 1.3 million times bigger than our earth.  Due to the sun's huge size, all members of the solar system are held by its gravitational pull and they revolve round it in their respective orbits.  Though, the distance between the earth and the sun is about 150 million kilometres, it is the nearest star to the earth as compared to other stars.  The rays of the sun reach the earth's surface in about eight minutes.  The Sun THE PLANETS Planets are the heavenly bodies which receive light and heat from the Sun.  They do not have their own light.  The total number of planets in the solar system are eight.  In the order of their distances from the sun, they are - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.  The first four planets in order of their distance from the Sun are- Mercury, Venus, Earth and Mars.  They are called the terrestrial planets because they have solid, rocky surfaces.  Two of the outer planets, Jupiter and Saturn, are known as gas giants whereas the more distant, Uranus and Neptune, are called ice giants.  Mercury has a thin atmosphere.  The days are very hot, but at night temperature drops hundreds of degrees below freezing point.  It is the smallest planet in our solar system.  Venus is the hottest planet due to its volcanic activities and thick atmosphere.  It spins backwards.  Earth, our home planet, is the only planet which supports life due to its optimum amount of heat, light and oxygen (Mars, known.

Page 5 Sun Saturn Venus Mars Neptune Mercury Earth Uranus Jupiter The eight planets in the order of their distance from the Sun as the Red Planet, is a cold desert.  Its atmosphere is too thin for liquid water to exist for long on the surface.  Jupiter, Saturn, Uranus and Neptune have rings.  The rings around Jupiter are very faint and hence, cannot be seen by naked eyes.  The atmosphere of Jupiter, Saturn and Uranus is mostly made up of hydrogen and helium.  Other than these gases, Uranus has methane, which gives blue tint to it.  Neptune is similar in composition to Uranus, composed primarily of hydrogen and helium along with traces of hydrocarbons and nitrogen.  It also contains a higher proportion of ammonia and methane.  Do you know?  STT TE.  Earlier Pluto was considered as the ninth planet.  In 2006, the International Astronomical Union (IAU) established a new category, dwarf planet, for Eris and Pluto.  The ring around the saturn were first seen by Galileo - a great astronomer of Italy, through his telescope in 1610 A.D.  The rotation time and revolution time of eight planets are as follows:.  Rotation Time Revolution Time around the Sun Planets Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune 59 days 243 days 24 hours Little over 24 hours 10 hours 10.7 hours 17 hours 88 days 225 days 365 days and 6 hours 687 days 12 years 29 years 84 years 165  years 16 hours

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THE EARTH - A UNIQUE PLANET 

The earth, on which we live, is placed at third position in order of the distance from the sun.  It ranks fifth in size.  The earth completes one rotation on its axis from west to east direction in about 24 hours, which makes one day.  Its revolution around the sun is covered in 365 days and 6 hours, which makes one year.  In ancient times, it was believed that the earth is a flat body, but in the fifth century CE, Aryabhatta, an Indian astronomer declared that the earth is spherical in shape.  Now, the photographs of the earth taken from the space confirm its spherical shape.  The earth bulges slightly at the equator and Photograph of the earth taken flattens at the poles.  from the space Now let us learn the favourable conditions which support life on the earth.  Firstly, the earth receives moderate heat and light from the sun.  This much quantity of heat and light is just sufficient to evolve and sustain all forms of life on the earth's surface.  Other planets ar either very hot or very cold.  Secondly, about two - third of earth's area is covered with water.  Water is essential for human beings, animals and plants.  No life can exist without water.  Thirdly, the earth has an envelope of air around it.  It contains gases, water vapors and dus particles which help in supporting life on the planet.  Earth's atmosphere protects us from the incoming meteoroids. 

Do You Know? 

On September 24, 2014, India became the fourth country in the world to reach the orbit of Mars and the first to achieve it in its first attempt!  Satellites the heavenly bodies that revolve around their respective planets are called Satellites.  Like the planets, satellites also do not have their own light and heat.  They reflect light, which they receive from the sun.  Each planet has one or more satellites, except the Mercury and the Venus.  Our earth has one satellite.  We call it the Moon.  As of 2015 Saturn has 53, Jupiter has 50, Uranus has 27 Neptune has 13 and Mars has 2 satellites. 

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THE MOON - OUR NEAREST COMPANION

The moon is the closest celestial body to the  earth.  Its distance from the earth is about 3,84,000 km.  The moon also enters light which it receives from the sun.  The moon rotates on its axis and also revolves around the earth.  The period of rotation of moon on its axis and that of revolution around the earth is the same, that is, 27.3 days.  Due to the same period of both the movements, only one side of the moon is visible from the earth.  The other side always remains invisible.  The moon has a barren land comprising of plains, valleys, and craters.  Scientists believe that long ago, earth collided with another space object and resulted in throwing a big chunk of rocky material into the space and that led to the Moon formation of the moon.  The moon does not have atmosphere around it.  It becomes extremely hot during the day time in the light of the sun and extremely cold during night or in shadow.  The temperature may increase to more than 214 ° C during the day and falls down to - 184 * C during the night.  Thus, no life can possibly exist on the moon.  Phases of the Moon We have already learnt that one side of the moon gets illuminated by the sun, which is visible to us.  The position of the moon in relation to the sun changes every day.  When the illuminated side of the moon is fully hidden from our view, it is called the New Moon (Amavasya)

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Do you know?  Astronaut Neil Armstrong was the first human to set foot on the moon.  He, along with Edwin Aldrin, landed the Lunar Module of Apollo 11 on the moon's surface on July 20, 1969.  The visible portion goes on increasing gradually day by day after the New Moon Day.  At the weft moon appears in crescent shape.  On eighth day, half portion of the moon comes in our view.  The full moon becomes visible after 15 days when half of its revolution is completed.  The day when the moon is completely visible to us, is the Full Moon Day (Purnima).  After this day, the decline of the moon's illuminated part starts.  The illuminated part slowly disappears and the moon again comes to the position of New Moon.  QOQOQO b 9 New Moon Full Moon New Moon Various phases of Moon The phases of the moon are used to determine the lunar dates and to fix the duration of lunar months in India and Arab countries.  The Hindu and the Muslim festivals, such as Deepawali and Eid, are usually fixed on the basis of lunar dates and months.  OTHER CELESTIAL BODIES IN THE SOLAR SYSTEM Apart from the sun, stars, planets and satellites, there are other celestial bodies also, like asteroids, meteoroids and comets, that revolve around the sun.  Asteroids are rocky, space objects that orbit our Sun. These can be a few feet wide to several hundred miles wide. Most asteroids orbit our Sun, a star, in a region of space between the orbits of Mars and Jupiter known as the  Asteroid Belt. Meteoroids 779314 Meteoroids are little chunks of rock and debris in space. They become meteors or shooting stars when they fall through the earth's atmosphere, leaving a bright trail as they are heated by the friction of the atmosphere) Most of them break up  in the atmosphere before they can strike the surface as meteorites.

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Do you know?  A crater is a depression which may be formed either by falling of a large meteor on the surface of the carth or by the volcanic eruption.  Meteor crater of North Arizona (USA) is nearly one mile across, 2.4 miles in circumference and more that 550 feet deep.  Comets Comets are the small bodies with a head and long luminous tail.  They are made up of dust and frozen gases, they appear in the sky after a long period.  A comet, known as Hailey's comet, appears in the sky after every 76 year interval.  Comet Hyakutake reached the closest point to earth in its path through the inner solar system on March 25, 1996 Keywords astronomers: scientists who study celestial bodies.  cluster a group of the similar elements gathered closely in a bunch.  srescent shape: a single curve that is broad in the center and tapers to a point at each end.  furnace: an enclosed chamber in which material can be heated at very high temperatures.  gravitational forces a force that attracts any object with mass.  self - luminous: objects having property of emitting light.  spherical: a shape slightly flattened at the top