UNIVERSE - III : LONG ANSWERS

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1. Write an explanatory note on Solar System with a diagram.
   
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   • Our solar system consists of the Sun, nine planets revolving around it, 91 satellites revolving around the planets, more than 1 lakh asteroids, comets, etc.
     
   • It is believed that the universe was formed due to Big Bang. After the big bang the sun was surrounded by a cloud of gases. These clouds were slowly converted into rocks due to contraction. These rocks kept on colliding with one another and during this process they either got broken or fused together to form bigger structures which we call planets. Thus, the present solar system came into existence.
     
   • The gravitational force of sun provides the centripetal force required to keep the planets in their orbits.
     
   • About 99% mass of the solar system comes is contained in sun. Sun is the main source of energy for planets. The amount of energy of sun reaching the earth is in desired proportion, essential for the origin and sustenance of life on earth.
     
   
   
2. Write a note on Sun.
   
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   • Sun is the center of our solar system.
     
   • About 99% of the mass of the solar system is contained in Sun. It mainly consists of hydrogen and helium along with elements like carbon, oxygen, magnesium, nickel, cobalt, etc.
     
   • It is the main source of energy for earth and other planets.
     
   • It is a sphere of hot gases with surface temperature of about 6000 K.
     
   • The 400 km thick, bright layer around the sun is known as 'photosphere'.
     
   • The layer beyond photosphere is invisible normally because the gases are very hot and less dense. But during solar eclipse, it becomes visible like a "crown". This layer is known as 'Corona'.
     
     
     
     
   • The temperature in the core region is about 1.5 crore (15 million) K. At this temperature, thermonuclear fusion process takes place in which four hydrogen nuclei fuse to form a nucleus of helium.
     
   • During this process some mass is lost which is converted into energy as per Einstein's mass-energy equation E = Δmc², where Δm is the lost mass and c is the speed of light in vacuum.
     
   • The mass of sun is 1.99 x 10³⁰ kg. This mass is called 'Solar Mass' (M₀).
     
   
   
3. Write a note on Mercury.
   
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   • It is the smallest planet of our solar system.
     
   • It is nearest to the sun, i.e. its orbit is the smallest.
     
   • Its mass is about (1/18)th the mass of the earth.
     
   • Its gravitational field is weak.
     
   • Its atmosphere is thin and consists mainly of vapours of sodium and potassium.
     
   • Its day temperature is 427°C and the night temperature is (-173)°C.
     
   • Its surface has many craters formed by meteors. Some of the craters are volcanoes.
     
   • It has no satellite.
     
   • Life is not possible on this planet.
     
   
   
4. Write a note on Venus.
   
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   • Considering the distance from sun, it is the second planet of our solar system.
     
   • It is a neighbour of earth and its composition is much similar to that of earth.
     
   • It is the most brilliant planet.
     
   • Its atmosphere consists of clouds of carbon dioxide.
     
   • Unlike other planets, Venus spins in opposite direction from east to west. Due to this the sun appears to rise in the west on Venus.
     
   • The core of Venus contains metals like iron and nickel whereas the crust is made of rocks containing iron, magnesium and silicate rocks.
     
   • Its surface contains large mountains, valleys and volcanoes.
     
   • It has no satellite (moon).
     
   
   
5. Write a note on Earth.
   
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   • Considering the distance from sun, earth is the third planet of our solar system.
     
   • It is the only planet of our solar system where life exists because it has a thin layer of atmosphere which extends up to about 800 to 1000 km.
     
   • Atmosphere protects us from meteors as they burn out due to friction before reaching the earth's surface.
     
   • The ozone layer of atmosphere blocks ultraviolet rays of solar radiation from reaching the surface and protects us from its harmful effects.
     
   • The natural Green House Effect due to gases like carbon dioxide and methane keeps the atmosphere warm enough to sustain life.
     
   • Due to all these favourable circumstances life originated and sustained on the earth.
     
   • The surface of the earth is solid (rocky) and has very large proportion of silicon dioxide.
     
   • The core region is made up of molten (semiliquid) mass containing iron, magnesium, silicates, etc.
     
   • It has one natural satellite (moon).
     
   
   
6. Write a note on Uranus.
   
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   • William Herschel discovered Uranus in 1781 AD.
     
   • It is 64 times bigger than earth.
     
   • Its diameter is 3.7 times that of the earth.
     
   • Its core contains iron, magnesium and silicate rocks.
     
   • It has layers of hydrogen and helium surrounded by icy clouds of methane and ammonia.
     
   • It has 9 narrow rings of ash colour.
     
   • It has 21 moons.
     
   • It cannot be seen with naked eyes.
     
   
   
7. Write a note on Pluto.
   
   ANS:[NOTE:(Only for information) Though we describe Pluto as a planet it has recently been removed from the list of planets due to certain reasons and at present it is no longer a planet. However, for us it is still a planet.]
   
   
   
   • It is cold, dark and yellowish.
     
   • Its density is similar to that of earth (therefore it is more like a terrestrial planet).
     
   • Its core contains silicate rocks surrounded by water, methane and carbon dioxide in the solid state.
     
   • Its outermost thin layer consists of nitrogen, methane and carbon dioxide.
     
   • Its atmosphere mainly consists of methane.
     
   • Its orbit is highly elliptical.
     
   • Pluto forms a binary system with its moon Sheron (actually 'Charon') and they revolve around their common centre of gravity.
     
   • It cannot be seen with naked eyes.
     
   
   
8. Distinguish between Jovian planets and terrestrial planets.
   
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9. Write a note on Asteroids.
   
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   • Asteroids are rocks with irregular shape(s) revolving around sun, which failed to assemble into planets (form planets) during the formation of the solar system.
     
   • They are found in the belt between the orbits of Mars and Jupiter.
     
   • There are about 1 lakh (0.1 million) asteroids.
     
   • Orbits of about 4000 asteroids are known.
     
   • Ceres is the largest asteroid known and it was the first asteroid to be discovered. Its diameter is about 1000 km.
     
   • Vesta is another asteroid which is luminous and has diameter of about 400 km. It was discovered in 1807 AD.
     
   • During their movement around sun, they sometimes collide with one another and get broken.
     
   • The debris of asteroids sometimes enters earth's atmosphere in the form of meteors which burn out due to atmospheric friction.
     
   • If a meteor is very large, it reaches the earth's surface. Then it is called a meteorite.
     
   • Asteroids contain silicon, nickel, chromium and calcium with possibly gold and platinum.
     
   
   
10. Write a note on 'shooting stars'.
    
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    • If a substance from space enters earth's atmosphere, it is called a meteor.
      
    • Such substances after entering earth's atmosphere burn due to friction and we see a streak of light in the sky.
      
    • Due to this meteors are called 'shooting stars', though they are not stars.
      
    • Maximum number of meteors are seen in the period between August and November.
      
    • If a large-sized meteor fails to burn completely after entering earth's atmosphere, it strikes the surface of the earth. Such an object is called a meteorite.
      
    
    
11. Write a note on Comets.
    
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    • In our solar system, there is a group of about a million celestial objects beyond Pluto which is called 'Cloud of Urt' [Wikipedia mentions it as : Cloud of Oort].
      
    • These objects revolve around sun in a highly elliptical orbit and are called Comets.
      
    • Comets are made up of dust and icy rocks.
      
    • When a comet comes closer to sun, the ice gets vapourised forming a luminous tail.
      
    • When the comet is nearest to sun, the tail is the longest and away from the sun.
      
    • As the comet moves away from sun, the tail starts becoming smaller and ultimately disappears.
      
    • Due to its tail a comet is called 'Tailed Star' despite the fact that it is neither a star nor is its tail permanent.
      
    • The orbits of more than 750 comets are known.
      
    • The most famous Halley's comet appears after a period of 76 years. It was last seen in 1986 AD and will be seen next in 2062 AD. It was named after Edmond Halley who had studied it in detail.
      
    • In 1997 AD, a brilliant comet 'Helibob'[Wikipedia mentions it as : Hale Bopp] was seen for about 19 months even with naked eyes.
      
    • A comet is basically made of water, carbon dioxide, ammonia, other frozen gases and dust particles.
      
    • A detailed study has shown that the tail of a comet contains molecules of CO and HCN. These molecules are essential for the formation of certain complex compounds required for the origin of life.
      
    • Some scientists believe that these molecules might have come to the earth from the tails of comets and resulted in the origin of life.
      
    • Ancient people believed that the arrival of a comet was responsible for war, epidemic and natural calamities like flood. Modern science has, however proved that the arrival of a comet is a normal event and there is nothing to panic about.
      
    
    [Only for Information : Recently a comet (McNaught) was seen in January 2007- See the Picture below.]
    
    
    
12. Write a few sentences on 'Stars'.
    
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    • Stars are self-luminous celestial objects which produce energy in the form of radiation due to the thermonuclear fusion process taking place within them.
      
    • Stars are hot gaseous spheres consisting mainly of hydrogen and helium.
      
    • Though stars appear to be permanent, they are born, they grow and they die.
      
    • The physical characteristics of a star change with time.
      
    • We observe stars of different colours. Stars appearing red have the lowest surface temperature and those appearing blue have the highest surface temperature. The colour and the surface temperature of a star depend on its phase.
      
    • Sun is the nearest star to us.
      
    
    
13. Distinguish between star and planet.
    
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14. Write a note on Nakshatras.
    
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    • An imaginary sphere covering the sky with the earth as its center is known as the Celestial Sphere.
      
    • The ecliptic of the celestial sphere is divided into 27 equal parts, each called a Nakshatra.
      
    • The angular region of a Nakshatra is 13° 20' [360/27].
      
    • Our moon covers angular displacement of about 13° 20' in one day along the ecliptic. Thus it remains for about a day in one Nakshatra.
      
    • Sun stays in one Nakshatra for about 13.5 days [365/27].
      
    • Nakshatras get their names on the basis of the imaginary figures(shapes) formed by luminous stars.
      
    • The Indian names of some Nakshatras are : Krittika, Bharani, Pushya, Magha, Ardra, Ashwini, Chitra, Vishakha, Swati, Rohini, etc. [The names given in the book : Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Saggitarius, Capricorn, Aquarius, and Pisces are in fact names of 12 Zodiac signs.]
      
    
    
15. Write a note on galaxy.
    
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    • Stars are found in big clusters called galaxies.
      
    • There are about 10¹¹ galaxies in the universe and each galaxy contains about 10¹¹ stars. Thus, there are in all about 10²² stars.
      
    • Galaxies have generally two types of shapes:(i)Spiral (ii) Elliptical. Some galaxies have irregular shape.
      
    • Most stars in elliptical galaxies are red indicating that they are very old. On the other hand the stars in spiral galaxies are bluish indicating that they are young. Thus, elliptical galaxies are older than the spiral galaxies.
      
    • The number of spiral galaxies is greater than that of elliptical galaxies.
      
    • The galaxy in which our solar system is situated is called the Milky Way. Milky Way appears as a milky belt stretching from North to South during dark night when the sky is clear.
      
    • Milky Way is spiral in shape when viewed from the top. When viewed from the sides, it is seen bulging at the center and tapered towards the ends.
      
    • The diameter of Milky Way is about 1 lakh (0.1 million) light years and the thickness of the middle (bulging) part is about 15000-20000 light years.
      
    • Sun (and therefore the solar system)is located at about 30000 light years away from the galactic center.
      
    • The sun completes one revolution around the galactic center in 22.5 crore (225 million) years at the speed of 250 km/s.
      
    
    
16. Explain in short the theories regarding the Constitution of Universe.
    
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    • Edwin Hubble showed that galaxies recede away from one another at a speed which is is directly proportional to the relative distance between them.
      
    • Based on this, it was concluded that the Universe is expanding continuously.
      
    • We can assume that the receding galaxies should have been together at one point in the past (where we can think of the Universe being of a definite size). At that time due to some huge explosion (Big-Bang), Universe came into existence (started expanding).
      
    • It has been estimated that the Big Bang might have taken place 13.7 billion years ago. Thus, the age of the Universe is 13.7 billion years.
      
    • According to another theory called 'Steady-State Theory', the Universe appears the same at all the time and remains unchanged. This theory cannot explain certain phenomena.
      
    
    
17. Write a note on Construction and Working of a space shuttle.
    
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    CONSTRUCTION:
    
    
    
    • A space shuttle appears like a huge plane.
      
    • It consists of three main liquid fuel rockets, a big liquid fuel tank which provides fuel to these rockets and two solid fuel rockets called booster rockets.
      
    • The outer surface of the space shuttle is made up of a special alloy to withstand extremely high temperatures.
      
    • It has a space to carry payloads and a robotic arm to perform functions in space.
      
    
    
    WORKING:
    
    
    
    • All five rockets ( two booster rockets and three liquid fuel rockets) are fired simultaneously.
      
    • The fuel of the booster rockets is used up before the shuttle reaches 45 km height and they get detached automatically and start coming down towards the earth.
      
    • The parachutes attached to them open up and control their speed so that they land slowly at a predetermined place in the sea. They are collected and reused after minor repairs.
      
    • The space shuttle continues to go up with the help of three rockets.
      
    • By the time the space shuttle attains its desired height the fuel tank becomes empty. It gets detached and during its journey towards earth it burns off due to friction.
      
    • Now the space shuttle starts revolving around the earth in its predetermined orbit.
      
    • A robotic arm released from its upper part performs required tasks.
      
    • A space shuttle can perform following tasks:
      
      
      
      • Launching a satellite in space.
        
      • Maintenance and relaunching of a satellite.
        
      • Bringing back a satellite from space.
        
      • Performing scientific experiments and observations in space.
        
      • Exchanging scientists in the space station and carrying equipment for them.
        
      
      
    
    
18. Describe various orbits for artificial satellites.
    
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    • Artificial satellites are kept in (i)Equatorial orbit (ii)Polar orbit.
      
    • The orbit which is parallel to the equator is known as Equatorial orbit.
      
    • If a satellite is placed at a height of 35786 km, its revolution period is 24 hours. Such asatellite is called 'Geostationary' as it appears stationary in space when observed from earth.
      
    • By proper arrangement of several geostationary satellites we can link all corners of the earth with one another.
      
    • Satellites in equatorial orbits do not require energy for revolutions.
      
    • The orbit which is parallel to the Meridian is called Polar orbit.
      
    • If a satellite is placed at a height of about 1000 km, its revolution period is about 2 hours. Such satellites complete several revolutions around earth in a day and they pass over a location on the earth at regular time interval.
      
    • Remote sensing satellites of India visit any location on the earth at the interval of 21 days whereas America's Landsat takes 16 days for that.
      
    • Like natural satellites, the orbits of artificial satellites are elliptical due to gravity effect.
      
    
    
19. Mention uses of artificial satellites.
    
    ANS:The uses of artificial satellites are as follows :
    
    
    
    • In communication : For telecommunication (telephone), television transmission, radio networks and computer networks (internet).
      
    • In Education Field : For teleconferencing and conducting country-wide classrooms.
      
    • In Weather Forecasting : Getting prior information about monsoon, climatic changes, cyclones, etc.
      
    • In Oceanography : To study changes occuring under sea and the aquatic life.
      
    • In Geological Surveys providing information about water resources, mineral resources, changes in earth's crust, etc.
      
    • In Agriculture to estimate the crop yield and to detect disease spread in crops.
      
    • In defence to keep an eye on the activities of enemy country.
      
    
    
20. Give details of Space Programmes conducted by ISRO.
    
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    • For communication, INSAT [Indian National SATellite system] series of satellites consisting of INSAT-1,2,3 have been launched. INSAT-4 is ready for DTH (Direct To Home) service for TV transmission.
      
    • For commercial purpose IRS [Indian Remoye Sensing satellites] series of satellites (IRS-I, IRS-P, etc.)have been launched.
      
    • METSAT [METeorological SATellite] is used for weather forecast.
      
    • Resource satellites are used for oceanography.
      
    • 'Cartosat' is used for geographical/geological surveys.
      
    • For astronomical observation Rohini series has been launched.
      
    • ISRO has developed PSLV (Polar Satellite Launch Vehicle) and GSLV (Geosynchronous Satellite Launch Vehicle) for the launching of different satellites.
      
    
    
21. Distinguish between polar orbit and equatorial orbit.
    
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