Earth in the solar system

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  • 1.1 THE EARTH IN THE SOLAR SYSTEMHow wonderful it is to watch the sky after sunset! OneLets Dowould first notice one or two bright dots shining in Youll need : 1 torch,the sky. Soon you would see the number increasing. 1 sheet of plainYou cannot count them any more. The whole sky is paper, pencil and afilled with tiny shining objects some are bright, others needle.dim. It seems as if the sky is studded with diamonds. Step :They all appear to be twinkling. But if you look at 1. Place the torch in the centre of the paper with its glassthem carefully you will notice that some of them dofront touching the paper.not twinkle as others do. They simply glow without2. Now draw a circle aroundany flicker just as the moon shines. the torch. Along with these bright objects, you may also see3. Perforate the paper with the needle within the circledthe moon on most of the days. It may, however, appear area.at different times, in different shapes and at different4. Now place the perforatedpositions. You can see the full moon only once in aboutcircle part of the paper ona months time. It is Full moon night or Poornima. A the glass front and wrap thefortnight later, you cannot see it at all. It is a New paper around the torch with a rubber band.moon night or Amavasya. On this day, you can watch5. Take care that the switchthe night sky best, provided it is a clear night.of the torch is not covered. Do you wonder why cant we see the moon and all6. In a dark room, stand atthose bright tiny objects during day time? It is because some distance facing athe very bright light of the sun does not allow us to seeplain wall. Switch off all other lights. Now flash theall these bright objects of the night sky. torch light on the wall. You The sun, the moon and all those objects shining inwill see numerous dots ofthe night sky are called celestial bodies. light on the wall, like stars Some celestial bodies are very big and hot. Theyshine in the night.are made up of gases. They have their own heat and7. Switch on all the lights in the room. All dots of lightlight, which they emit in large amounts. These celestial will be almost invisible.bodies are called stars. The sun is a star. 8. You may now compare the Countless twinkling stars in the night sky aresituation with what happenssimilar to the sun. But we do not feel their heat or to the bright objects of thelight, and they look so tiny because they are very very farnight sky after the sun risesfrom us. in the morning.

2. You must have noticed that allobjects look smaller when seen from adistance. How small an aeroplane lookswhen it is flying at a great height!While watching the night sky, youmay notice various patterns formed bydifferent groups of stars. These arecalled constellations. Ursa Major orBig Bear is one such constellation. Oneof the most easily recognisableconstellation is the small bear orSaptarishi (Sapta-seven, rishi-sages). Itis a group of seven stars (Figure 1.1)that forms a part of the large Ursa MajorConstellation. Ask someone elder inyour family or neighbourhood to showyou more stars, planets andconstellations in the sky.In ancient times, people used todetermine directions during the nightwith the help of stars. The North starindicates the north direction. It is alsocalled the Pole Star. It always remainsin the same position in the sky. We canlocate the position of the Pole Star withthe help of the Saptarishi. Look at Figure 1.1. Youwill notice that, if an imaginary line is drawn joiningthe pointer stars and extended further, it will point tothe Pole Star.Some celestial bodies do not have their own heatFigure 1.1 : Saptarishi and the and light. They are lit by the light of the stars. SuchNorth Starbodies are called planets. The word planet comes fromthe Greek word Planetai which means wonderers.The earth on which we live is a planet. It gets all itsheat and light from the sun, which is our nearest star.If we look at the earth from a great distance, say the Interesting Fact moon, it will appear to be shining just as the moon. Jupiter, Saturn andThe moon that we see in the sky is a satellite. It is a Uranus have ringscompanion of our earth and moves round it. Like our around them. These earth, there are eight other planets that get heat andare belts of small debris.light from the sun. Some of them have their moons too.These rings may beseen from the earth THE SOLAR SYSTEMwith the help of powerful The sun, nine planets, satellites and some othertelescopes. celestial bodies known as asteroids and meteoroids 2THE EARTH : OUR HABITAT 3. THE EARTH IN THE SOLAR SYSTEM 1. MERCURY - One orbit around sun - 88 days, 5. JUPITER - One orbit around sun - 11 years, 118. NEPTUNE - One orbit around sun - 164 years.One spin on axis - 59 days.months about 12 years. One spin onOne spin around axis - 16 hours 2. VENUS - One orbit around sun - 255 days. axis - 9 hours, 56 minutes, number of 7 minutes, number of moons - 8.One spin on axis - 243 daysmoons - 16 9. PLUTO - One orbit around sun - 248 years. 3. EARTH - One orbit around sun - 365 days.6. SATURN - One orbit around sun - 29 years, 5 One spin on axis - 6 days 9 hours,One spin on axis - 1 day months. One spin on axis - 10 hours 40number of moons - 1Number of moons - 1minutes, number of moons - about 18. 4. MARS- One orbit around sun - 687 days 7. URANUS - One orbit around sun - 84 years. OneOne spin on axis - 1 day,spin around axis - 17 hours 14 minutes,number of moons - 02 number of moons - about 17.Inner planets - very close to the sun. They are made up Outer Planets - Very-very far from the sun and are huge planets made up of gases and liquids.of rocks. 3Figure 1.2 : The Solar System 4. Do you know? form the solar system. We often call it a solar family, with the sun as its Head. Sol in Roman mythology isThe Sun the Sungod.Solar means related toThe sun is in the centre of the solar system. It is hugethe sun. The family of theand made up of extremely hot gases. It provides thesun is, therefore, calledpulling force that binds the solar system. The sun isthe solar system. Writethe ultimate source of heat and light for the solardown as many words using system. But that tremendous heat is not felt so muchthe word solar.by us because despite being our nearest star, it is farWord Originaway from us. The sun is about 150 million km away from the earth.Many words usedin a language may Planetshave been takenfrom some other language.There are nine planets in our solar system. In order ofGeography, for example, is their distance from the sun, they are: Mercury, Venus,an English word. It has itsEarth, Mars, Jupiter, Saturn, Uranus, Neptune andorigin in Greek, which Pluto.relates to description ofthe earth. It is made ofAn easy way to memorise the name of the planets intwo Greek words, ge order of their distance from the sun is:meaning earth andgraphia meaning writing.MY VERY EFFICIENT MOTHER JUST SHOWED US NINE PLANETS.Find out more about theearth.All the nine planets of the solar system move around the sun in fixed paths. These paths are elongated. They are called orbits. Mercury is nearest to the sun. It takes only about 88 days to complete one round along its orbit. Pluto is supposed to be farthest till now. So it takes about 248 years to complete one round. Venus is considered as Earths-twin because its size andDo you know? shape are very much similar to that of the earth. Humans haveA new planet 2003 UB 313 has been discovered alwaysbeenrecently in our solar system. It is bigger than Pluto fascinated gazing and farthest from the Sun. But other details aboutat the night sky. Those whothis planet are not yet available. Hence, the name ofstudy the celestial bodies this planet has not been included.and their movements arecalled astronomers. The EarthAryabhatta was a famousastronomer of ancientThe earth is the third nearest planet to the Sun. InIndia. Today, astronomerssize, it is the fifth largest planet. It is slightly flattenedall over the world are busyat the poles. That is why, its shape is described as aexploring the universe.Geoid. Geoid means an earth-like shape.4THE EARTH : OUR HABITAT 5. Conditions favourable to support life are probably Do you know?found only on the earth. The earth is neither too hotLight travels atnor too cold. It has water and air, which are verythe speed ofessential for our survival. The air has life-supporting about 300,000gases like oxygen. Because of these reasons, the earthkm per second.is a unique planet in the solar system. Yet, even with this speed,From the outer space, the earth appears bluethe light of the sun takesbecause its two-thirds surface is covered by water. Itabout eight minutes tois, therefore, called a blue planet.reach the earth.The MoonOur earth has only one Interesting Factsatellite, that is, themoon. Its diametre isNeil Armstrong wasonly one-quarter that of the first man tothe earth. It appears so step on the surfacebig because it is nearer to of the moon on 29 Julyour planet than other 1969. Find out whetherany Indian has landed oncelestial bodies. It isthe moon?about 3,84,400 km awayfrom us. Now you cancompare the distance of Figure 1.3 : The moon as seen fromthe spacethe earth from the sunSatellite is a celestialand that from the moon. body that moves aroundThe moon moves around the earth in about 27 days. the planets in the sameIt takes exactly the same time to complete one spin. As way as the planets movea result, only one side of the moon is visible to us on around the sun.the earth.Human-made Satellite isThe moon does not have conditions favourable foran artificial body. It islife. It has neither water nor air. It has mountains, designed by scientists togather information aboutthe universe or forcommunication. It iscarried by a rocket andplaced in the orbit aroundthe earth.Some of the Indiansatellites in space are INSAT,IRS, EDUSAT, etc.? What do animals andRocket launch Rocket falls back to the Earth Satellite enters orbit plants require in orderFigure 1.4 : Huma