5 Editorial6 The Universe6 Theories of Space7 The Space and Outer Space9 Modern Astronomy

10 Astronomical Terms11 The World of Sound12 Galaxies14 Our Home Galaxy : The Milky Way15 The World of Stars17 Constellations18 Magnitudes18 Life of a Star20 The Solar System21 Other Planetary Systems22 The Sun24 The Inner Planets27 The Outer Planets30 Satellites or Moons31 The Earth’s Moon32 Satellites34 The Comets36 The Asteroids36 Shooting Star or Meteoroids38 The Earth38 The Origin of the Earth41 The Age of the Earth42 Movements of the Earth43 Spherical Coordinates of Earth46 The Time48 The Time Zones49 The Internal Structure of the Earth52 Lithosphere56 Continental Drift58 Plate Tectonics60 Landforms64 Exogenetic (Exogenic) Forces65 Unconformity67 Earthquakes

72 Effusive Magmatism or Volcanism73 Effusive Magmatism73 Volcanic Structures77 Intrusive Magmatism or Plutonism79 Major Land Surface Types81 Deserts83 Islands85 Gradation or Denudation85 Weathering88 Erosion89 Denudation and Accumulation Agents90 The Wind90 Waters of the Surface Run-off92 Waters of the Sub-surface Flow97 Snow and Ice

100 Geographic Distribution ofContemporary Glaciers

104 The Hydrosphere104 The World Ocean : General106 Relief Features of the World Ocean

Floor110 The Temperature of the Sea Water111 Salinity of Oceanic and Sea Waters112 Chemical Composition of Seas and

Oceans113 Gases in Oceanic and Sea Waters114 Organic Marine Life115 Sea Water Pressure and Density115 The Movement of the Sea Water117 Tides120 Ocean Currents121 General Information about Rivers123 Major Riverside Cities124 Longest Rivers of the World125 Highest Waterfalls of the World128 Lakes136 Swamps and Their Geological

Significance

Geography / 3

139 The Atmosphere139 The Significance of our Atmosphere140 Atmospheric Layers143 Atmospheric Elements143 Solar Energy144 Heating of the Atmosphere145 The Heat Energy Budget146 Air Temperature147 Temperature of the Atmosphere148 Vertical Distribution of Temperature150 Horizontal Distribution of Temperature152 Atmospheric Pressure152 Measurement of Air Pressure154 Variations in Atmospheric Pressure157 Wind158 The Wind Systems162 Air-Masses167 Tropical Low Pressure Systems168 Special Winds171 Land and Sea Breezes172 Some Other Winds174 Humidity and Precipitation174 Water-Vapour in the Atmosphere175 Instability177 Condensation179 Types of Fog180 Clouds182 Rainfall184 Types of Rainfall186 Other Forms of Precipitation188 Climatic Types189 Climatic Types196 Biosphere200 Ecology204 Pollution206 Antipollution Measures207 Evolution207 Geological History

208 The Pre-Cambrian Era209 Palaeozoic Era209 Mesozoic Era209 Caenozoic Era210 Quaternary Era211 Geological and Biological Changes217 Human Geography220 Life in Tropical Deserts223 Tribes in India230 Races of World231 World Population236 Population Problems238 Urban Settlements239 Economic Geography240 Agriculture253 Industries258 Transport and Communication263 Geography of India264 Rivers264 Main Rivers of India268 Climate269 Vegetation271 Soils272 Source of Irrigations273 Multipurpose Projects in India278 Agriculture286 Minerals288 Major Industries293 Environmental Degradation297 India’s Population–2011 (Final)299 Final Population Table of Census of

India–2011300 Working and Non-Working Population

of India Census–2011301 Scheduled Caste and Scheduled

Tribe Population of IndiaCensus–2011

302 Some Special Facts on Population2011

314 Objective Questions

Geography / 4

The concurrence of the views of the Editor is not necessary for any matter or figure published in Pratiyogita Darpan. —Editor

Geography/5

Ashish was considered a spoiledchild. His parents lived below thepoverty line. Although he was astudent of class VIII, yet he hadnothing to do with books. He threwstones at the passers-by. Children didnot dare to play on the road in hispresence. He bullied them. Almost,the whole class disliked him. Forpractical purposes he was brandedas a terrorist.

Unfortunately, a communal riotbrokeout and the rioters did all theycould do against members of theother community. Ashish saw, asmany others did, that one of therioters was molesting a young girl andintended to rape her. Ashish lost notime to help the girl. The rioters weremany, Ashish was alone. He wasbadly injured, but he freed the girlfrom the clutches of that goonda. Inhis dying statement before the policehe said that he lived a useful life ashe had been able to save the honourof one of his sisters. Ashish taught usa lesson in humanism and manhood.Honour of women should be the mostvaluable thing to us, more valuablethan our own life.

We would say that good personshave always to give us a good lesson,provided we are ready to receive it.Our young men and women ! thedivine spark is in everyone’s heart.Try to recognize it and give expres-sion to that within your limits.

A great teacher has said, no manis your enemy; no man is your friend;all alike are your teachers. Thismeans that in case we are aware andreceptive, we can learn somethingfrom everybody and for the matter ofthat, from everything and every event.Therefore, the same principle applies

to all circumstances, events and situa-tions in which we find ourselves. So,there are no hostile circumstances orsituations and no congenial ones. It isbecause of our preconceptions andmental inclinations and desires thatthe circumstances or situations appearto be adverse or favourable. It is onlyin the absence of such mental reac-tions that there may be an opportunityto see the beneficial element con-tained in them or hear the messagewhich they have to give. Let us besure that there is the great plan ofnature which helps everything andcreature to evolve. We should, there-fore, develop the necessary insightand mental attitude to learn some-thing useful from every event andperson that we have to interact with.

When the thought arises thatsomebody is not a friend or somecircumstance is adverse, it is surelynothing but an opinion—more subjec-tive than objective. Such opinions areassociated with our selfish desires,This is a part of the darkness ofignorance. All attractions and repul-sions are part of delusion, whichonly misguide us. There is a trapof delusion everywhere. We must,with a detached mind, try to see whatgood lesson we can learn from theperson before us or the situation inwhich we have been placed. Grumbl-ing and murmuring is against the Lawof Progress. Landing oneself in pairsof opposites, such as friend and foe,victory and defeat, etc., the personconcerned fails to see things inperspective. His virtue is clouded byour narrow self. The flame of themind continues flickering ceaselesslyunder the impact of the wild winds of

the opposites—likes and dislikes,favourable and adverse, friend andfoe and so on. Teachers and scrip-tures of nearly all religions lay em-phasis on submission to the divinewill. At this point, we may tell ouryoung readers not to get startled atthe mention of divine will. We are nottalking metaphysics but the ways ofthe worldly submission to divine willimplies that we do not react. Weshould take things calmly and keepour minds steady. In due course, youwill realise that the thought side ofscience is philosophy and the actionside of it is religion. Therefore, wewould like to advise you to look at theevents such as a scientist watchesminutely the outcome of his experi-ment with an unconditioned and objec-tive mind. Even if the experiment doesnot give result as he expected, thefindings in it help him when he under-takes the experiment for the nexttime. In case you develop this positivemental attitude, you will get light atevery step in your life and go a longway in whatever you undertake to do.

We can enrich our knowledgeand wisdom, if we recognize that lifeis teaching in the form of a friend orenemy. To receive the teachings oflife we have to shed prejudices andlikes and dislikes, preconceptions andprior judgements whether we are inIndia, England, America or someother country. Can you make up yourmind to go through life with a recep-tive mind. All are your teachers—nofriend, no enemy. Remember that it isthe receptive mind where the twogreat attributes of a great personalitydwell prudence and a sense ofdiscrimination. ●●●

Geography/6

THE UNIVERSETHE UNIVERSETHE UNIVERSE

Man was born on this earth.During the course of evolution his lifehas been indebted to the soil, water,air and landscape of Mother Earth.He has had very close and intimaterelations with his environment. Tohim, his home–the Earth has beenthe most important thing in the wholeof the Universe.

When the Universe was firstconceived of as an orderly unit, it wascalled Cosmos, and the studiesrelating to the cosmos were known asCosmogony or Cosmology. Todaywe speak of them as Space andSpace Sciences.

The Universe or the Cosmos, asperceived today, consists of millionsof Galaxies. A galaxy is a hugecongregation of stars which are heldtogether by the forces of gravity. Mostof the galaxies appear to be scatteredin the space in a random manner, butthere are many galaxies whichremain clustered into groups.

Our own galaxy, called the‘Milky way’ or ‘Akash ganga’, whichappears as a river of bright lightflowing through the sky, belongs to acluster of some 24 galaxies called the‘Local group’. The Milky Way ismade up of more than a hundredbillion sparkling stars, which, thoughquite distant from each other, seemfrom the Earth as having been placedclose together.

The two other nearest galaxiesare the Large Magellanic Cloud andthe Small Magellanic Cloud, namedafter Magellan, who discovered them.

The Universe is infinite, both intime and space. It was around sixthcentury BC that men started enquiringinto the mysteries of the Universe inan endeavour to rationally analysethe earthly and the heavenly pheno-mena. Ancient Greek astronomersand mathematicians came up with theview that the Earth was a perfectmotionless sphere, surrounded byeight other crystalline spheres. TheSun, the Moon, and the five knownplanets, viz., Mercury, Venus, Mars,Saturn and Jupiter, revolved around

the Earth on seven ‘inner spheres.The stars were permanently fixed tothe ‘outer sphere’ that marked theedge of the Universe.

The culmination of Greeks know-ledge is associated with the nameof Claudius Ptolemy of Alexandria,AD 90 to 168. In second century(AD 140) Ptolemy, a Graeco-Egyptianastronomer, synthesised the variousdata gathered by the early Greekastronomers. Ptolemy, in his book‘Almagest’, presented his system ofastronomy based on a geocentric(Earth-centred) Universe. He main-tained that the Earth was the centreof the universe, and the Sun andother heavenly bodies revolvedaround the Earth.

In 1543, Polish astronomerCopernicus argued that the Sun notthe Earth, was the centre of theUniverse. Though the Copernicustheory changed the centre of theUniverse it did not change its extentwhich was still equated with the Solarsystem. It took another three and halfcenturies before our ideas changedfurther.

By 1805 telescopic studies madeby the British astronomer Herschel,made it clear that the Universe wasnot confined to the Solar system.The Solar system itself was only apart of a much vaster star systemcalled the Galaxy. The Universe thusbecame quite extensive comparisingmillions of stars scattered about theMilky Way. But our vision of theUniverse did not end there.

As the 20th century opened, itseemed that the Milky Way galaxywith its cluster of over a hundredbillion stars together with theirattendant satellites, the Magellanicclouds, actually represented all therewas to the Universe.

HUBBLE’s Law :Edwin Hubble in 1924 showed that

nabulae were distant galaxies. In 1929,he found the speed a galaxy movesaway from earth depends on itsdistance from earth. If a galaxy is 5times as far away as another, it ismoving away 5 times faster.

In 1925 American astronomerEdwin P. Hubble (1889–1953)—pointed out that there were othergalaxies in the Universe and that theUniverse actually consisted ofmillions of galaxies like the MilkyWay. In 1929 Hubble proved thatthese galaxies are flying away fromeach other and that the farther theyare, the faster they fly.

Doppler Effect :

The movement of a star or a galaxyeffects its light as seen by an observer.If the star is moving towards theobserver, its light will be shifted towardsthe blue end of the spectrum, if the staror galaxy is moving away from theobserver its light will be shifted to thered end of the spectrum. This is knownas the Doppler Effect or Shifts TheDoppler Shifts of galaxies show thatthey are receding and that the Universeis in a state of rapid expansion.

THEORIES OF SPACEModern theories of the Universe

are based on this flight of galaxies,that is, on the assumption that matteris in a state of rapid expansion.

THE EXPANDING UNIVERSEIt is a general law that all

material bodies are heated whencompressed and cooled whenexpanded. The primordial Universe,being highly compressed, must have

experienced high temperatures. Heat,as we know, tends to expand matter.High temperatures, therefore, musthave, at some point, started an

Geography/7

expansion of the Universe. It is thisexpansion which is continuing evennow. All theories of space (Universe)seek to explain the nature andconsequences of this expansion.

BIG–BANG THEORY

Opposing cosmological theories,the first credit goes to a Belgianastronomer–priest, Abbe GeorgesLemaitre. He explained this processof expansion, in what is known as‘the evolutionary theory’ or ‘thebig-bang theory’. He argued thatbillions of years ago, cosmic matter(Universe) was in an extremelycompressed state, from whichexpansion started by a primordialexplosion. This explosion broke upthe superdense ball and cast itsfragments far out into space, wherethey are still travelling at thousands ofmiles per second. It is from thesespeeding fragments of matter that ourgalaxies have been formed. Theformation of galaxies and stars hasnot halted the speed of expansion.And, as it happens in all explosions,the farthest pieces are flying thefastest.

The primordial explosion is thehallmark of the big-bang theory. Italso differs from other theories in twoimportant respects : (i) it disagreeswith the Seady State claim, that newmatter is being continuously createdin the Universe, (ii) it differs from thePulsating theory, in that, it does notadmit, that matter will revert to theoriginal congestion point, from whichthe primordial explosion started.

STEADY STATE THEORY

This theory originally advancedby two astronomers, Hermann Boudiand Thomas Gold, has since receivedsupport from the British astronomer ofCambridge University. According tothis theory, which is also known asthe Continuous Creation Theory,galaxies recede from one antoher buttheir spatial density remains constant.The Universe everywhere remainedrelatively uniform, unchanged, withoutbegining or end. That is to say, as oldgalaxies move apart new galaxies arebeing formed in the vacancies. Thesenew galaxies are formed from newmatter which is being continuouslycreated to replace old matter that isbeing dispersed. This concept, desig-ned to get around the philosophic

hurdle of a Universe with finitebegining and end, is known as the‘Steady State Theory’.

Later the big-bang theory wasdefined to clear the hardle offinitenes, too : its advocates proposeda ‘pulsating’ or ‘oscillating’ Universethat periodically expands from theexplosion of a primordial body, thencontracts back and explodes again,over unmensely long cycles, adinfinitum.

PULSATING (OSCILLATING)UNIVERSE THEORY

According to this theory,advocated among others by Dr. AlanSandage, the Universe expands andcontracts alternately between periodsrunning into tens of billions of years.Dr. Sandage thinks that some 12billion years ago a great explosionoccured in the Universe and that theUniverse has been expandingeversince. It is likely to go onexpanding for 29 billion years more,when gravitation will halt furtherexpansion. From then on, all matterwill begin to contract or collapse uponitself in a process known as‘implosion’. This will go on for 41billion years compressing matter intoan extremely superdense state andthen it will explode once again. This isthe latest theory of the evolution ofthe Universe.

THE ANTI–UNIVERSE

Existence of anti-Universe,somewhere in the cosmos, with itscharacteristics reversed to thosenormally found in this Universe, isnow considered a possibility. This hascaused a star in the scientific worldtoday.

Recent discoveries of particles ofanti-matter have led scientists toconsider the possibility of theexistence of an anti-Universesomewhere in the cosmos. The highlyabstruse theoretical physics dealingwith the principles of SymmetryLaws suggested that processes,phenomena and events happening inthis Universe must have theircounterparts in the reverse manner inanother Universe which we may call‘anti-universe’. If a fundamentalparticle exists in this Universe, wemust have a similar particlesomewhere in the cosmos but will be

like one as seen by reflecting it in amirror. The ‘time-event’ will also bein a reverse manner, that is, the reelof time will be functioning in thereverse direction to that going on inour Universe. The ‘future-events’ inthe anti-Universe are perhaps the‘past-events’ in this Universe.

It is still not quite clear how farthis left-right symmetry of the mirror-image reflexion is being followed inthe anti-Universe in some types ofphysical phenomena results ofinvestigations indicate that the exactsituation is much more complex andcomplicated. But still the scientistsare becoming more and moreconvinced that a mirror-image-likeanti-world, precisely identical to ourworld but as reflected in a mirror,exists somewhere in the Universe.

THE OPEN OR CLOSED UNIVERSE

That the Universe is expanding istoday considered established. Aquestion that remains unsettled iswhether the expansion will continuefor ever or whether the recedinggalaxies will some day stop and thenreverse their motion, eventually fallingtogether in a great collapse. Theanswer to this question determinesthe geometrical character of theUniverse, that is, it determines thenature of space and time. If theexpansion continues perpetually theUniverse is ‘open’ and infinite; if it willsome days stop and reversedirection, the Universe is ‘closed’ andof infinite extent.

THE SPACE ANDOUTER SPACE

The difference between spaceand outer space is that (i) the term‘space’ is used to denote the entire‘Universe’, that is, the Earth and itsatmosphere, the Moon, the Sun andthe rest of the Solar System with itsother planets and their satellites andall the stars and galaxies spread overthe infinite skies; and (ii) the ‘outerspace’ refers to the entire spaceexcept the Earth and its atmospherethe outer space begins where theEarth’s atmosphere ends, and ifextends in all directions from abovethe atmosphere of the Earth.

Outer space is infinite. Ourterrestrial units of measurements

Geography/8

hardly suit its dimensions. So wehave evolved new units ofmeasurement like the ‘Light Year’and the ‘Astronomical Unit’.

LIGHT YEARA Light Year is the distance

covered by light in on year in vacuumtravelling at a speed of 299,792·5 Kmper second or about 186,282 milesper second. (This velocity wasaccepted as one of the AstronomicalConstants by the InternationalAstronomic Union in 1968). A lightyear is thus 5·88 × 1012 miles.

ASTRONOMICAL UNIT (A. U.)A new unit in space dimensions

has been evolved by radar astronomy.This unit is called ‘Astronomical Unit(A. U.)’. The symbol ‘AU’ isrecommended by the InternationalBureau of weights and measures. Itrepresents the mean distance bet-ween the Sun and the Earth,calculated on the data supplied byrdars. This distance–the AstronomicalUnit–has now become a key constantin determining distances in the SolarSystem.

Astronomical Unit in terrestrialmeasurements is approximately 93million (92,857,000) miles or 150million (149,598,000) kilometres.Interms of space dimensions, we maysay that a Light Year is made up ofabout 63,241·1 astronomical units.

The new technique is likely torevise our established ideas of spacedimensions based on the speed oflight. It is now known that the velocityof a radar pulse is accurate to onepart in 100 million, whereas thevelocity of light is known only to beaccurate to one part in a million. Thismeans that the error in radar readingis only one-hundredth of what it wouldbe in light measurements.

TRACKING OUTER SPACELight and sound are the two

principal media through which wegather our impressions of the externalWorld. Light is something we can see(visible) and sound is something wecan here (audible). This wasconsidered an axiomatic truth till theend of the 18th century. As the 19thcentury broke, this simple belief wasshattered. Astronomers and physicistslearned that these are invisible lightsand inaudible sounds. The first breakcame in 1800 when the British

astronomer William Herschel (738–1822) discovered infrared radiation.

THE SOLAR SPECTRUMWhen sunlight (white light) is

passed through a prism it is brokenup into rays of different colours, likethose of the rainbow. Traditionally,seven colours are known, which areepitomised by the acronymVIBGYOR, that is, VIOLET, INDIGO,BLUE, GREEN, YELLOW, ORANGEand RED. This is called the SolarSpectrum, with the violet at one endand the red colour at the other end. Instudying the heating effects of theSolar Spectrum, Herschel placed athermometer in each of the colours ofthe spectrum and an extra thermo-meter outside the spectrum at the redend. The thermometer outside thespectrum (at the red end) showed ahigher degree of heat than any otherinside the spectrum. He called theserays “infra-red” (below the red) rays.

In 1801 the German physicistJohann Ritter (1776–1810) discove-red that the rays outside the spectrumat the violet end, broke down silverchloride more quickly than the rayswithin the visible spectrum. Thesecame to be called ‘ultra-violet’(beyond the violet) rays. It thus turnedout that sunlight formed not only avisible spectrum but also an invisibleone.

ANGSTROM UNITIn 1803 Thomas Young (1773-

1829), a British physicist, showed thatlight travelled in tiny waves of varyingwavelengths. The waves were toosmall to be measured by conventionalscales. So Anders Angstrom (1814–1874), a Swedish physicist, evolved anew scale to measure wavelengths.He chose a unit equal to ten-billionthsof a metre. This has since becomeknown as the ‘Angstrom Unit’. TenAngstroms are equal to a milli-micrometre (a thousandth of amillionth of a metre) which in termsof modern SI units is equal to a‘nanometre’.

ELECTRO–MAGNETIC SPECTRUM

The invisible ultra–violet andinfra-red radiations remained inexpli-cable till James Clark Maxwell (1831–1879), the British physicist, cameout with his ELECTRO-MAGNETICTHESIS in 1870. Maxwell argued thatelectricity and magnetism were

different aspects of a single dectro-magnetic field. Periodical variations in

The wavelengths of theelectromagnetic spectrum inmodern international units

10 Angstroms = 1 nanometer

1000 nano = 1 micrometre

1000 micro = 1 millimetre

10 milli = 1 centimetre

10 centi = 1 decimetre

10 deci = 1 metre

the electro-magnetic field producedelectro-magnetic radiations of varyinglengths. The visible light is only onepart and for that matter a very smallpart of the electro-magnetic spectrum.He also postulated that there can beother invisible radiations of muchshorter wavelength than the ultravioletat one end and for longer than thewavelength of the infra-red at theother.

Visible CentralLight Wavelengths

Violet 410 nano

Blue 470 ”Green 520 ”Yellow 580 ”Orange 600 ”Red 650 ”

The maxwellian theory wasvindicated when the German physicistHeinrich Hertz (1857–1895) producedelectro–magnetic radiations withwavelengths much longer than that ofthe infra-red rays. These radiationswere at first called ‘Hertzian Waves’but eventually came to be know as‘Radio Waves’. Then in 1895,another German physicist WilhelmRontgen (1845–1923) discoveredwhat be called ‘X-ray radiation’. The‘X-ray’ was later found to be muchshorter in wavelength than the ultra-violet rays.

In 1896, the French physicistHenri Becquerel (1852–1905)discovered the phenomenon of‘Radio Activity’. Becquerel did not atthat time know why or in what mannerthis radio activity took place. Sub-sequently it was found that this radioactivity was caused by the atoms ofthe heavy metal ‘Uranium’ giving offa constant emission of radiation andparticles. It was further shown thatthis radio activity was also electro-magnetic in nature. Rutherford namedit the ‘Gama Ray’. The gama ray had

Geography/9

a wavelength even shorter than thatof the X-ray.

PHOTONS

In 1905 Einstein showed that allforms of radiation travelled in wavepackets, which acted like particles insome ways. He called these packets‘Photons’. The energy of the photonsincreases as the wavelengthdecreases. The wavelength is relatedto frequency, that is to say, thenumber of vibrations or waves orcycles per seconds. The shorter thewavelength, the higher is thefrequency and the greater the energy.Thus “gamma rays” with the shortestwavelength (below 0·01 nanometre)are the most energetic. The energydecreases as the wavelengthincreases, through X-ray (1 to 0·01nanometre), ultra-violet (1 to 400nanos) visible light in all the coloursof the spectrum (400 nanos to 700nanos) infra-red (700 nanos to 1milimetre) micro-waves (1 millimetreto 500 millimetres or 50 centimetres)to radio waves which have thelongest wavelengths (50 centimetresto 3000 centimetres or 30 metres)and the lowest energy content.

THERMAL RADIATION

Every object which is at atemperature above ‘Absolute Zero’(–273·16°C) radiates photons of allkinds. The average energy of thephotons emitted increases with thetemperature. We experience this heatduring the peak period (noon) invisible light radiation. But evenobjects which are not hot enough toglow like the sun still radiatequantities of infra–red radiation, forinstance, our own bodies. The bodytemperature, that is, cool bodies,radiate micro waves and longer radiowaves. These radions, called ‘ther-mal radiations’, can indicate thetemperature levels of the objectsemitting them.

RADIO WAVES

Radio waves are the radiationswith the longest wavelengths, that isfrom 50 centimetres to as much as 30metres. Objects in outer space thatemit such radiations are called‘Radio Sources’.

WINDOWS ON OUTER SPACE

The atmosphere of the earth islike a sieve which allows only some

wavelengths from outer space toreach us. Sunlight forms one group ofwavelengths which come downthrough the atmosphere. This inclu-des not only the visible light but alsoa port of the invisible light, namely,the near ultraviolet (400 to 300nanos) and the near infrared (700 to2500 nanos). This is one of thewindows that opens out on outerspace.

MICRO–WAVE WINDOW

The other window is called the“micro-wave window”. This windowcovers all wavelengths from onemillimetre to 30 metres. Theexistence of the microwave windowwas not particularly noticed or studiedtill 1932 when Karl Jansky of the BellTelephones announced that he hadreceived radio messages from outerspace.

MODERNASTRONOMY

Modern astronomy began withthe Italian astronomer GALILEO1564–1642. In 1609 Galileo heard ofthe telescope made by the DuchamanHans Lippershey. Galileo improvedupon it and constructed a similarinstrument that could magnify uptothirty diameters.

OPTICAL ASTRONOMY

It was this thirty diameterinstrument, known as ‘REFRACTORTELESCOPE’, that opened the fieldof optical astronomy. Galileo madeseveral stasting discoveries. Hefound the Moon’s surface to berugged and the Pleiades to containover 40 stars. He discovered four ofJupiter’s moons and observed thesunspots.

In 1668 NEWTON invented anew instrument ‘The REFLECTORTELESCOPE’. In a refractor tele-scope light is gathered by a largeobjective lens. In a reflector telescope,a large curved mirror is used for thispurpose. Both these types of opticaltelescopes are still in use.

GROWTH OF MODERN ASTRO-NOMY

The invention of the opticaltelescope was an epochal event inthe history of astronomy. Theinstrument so caught the fancy of the

astronomer and the layman alike, thatall advanced countries vied with oneanother in building bigger and biggertelescopes.

RADIO ASTRONOMY

Radio Astronomy came intobeing in the most unexpectedmanner. In 1931, Karl Jansky, anUS radio engineer working with BellLaboratory, noticed a steady streamof radiation coming in from outerspace. It also attracted the attentionof an amateur radio operator in US,Grote Reber, worked single, handedfor nearly ten years, studying the skyand analysing radiations. In 1937, hebuilt the world’s first Radio Tele-scope–a 31 feet 5 inches parabolicdish–and set it up in his backward atWheaton Illinois. In 1940 be produceda radio map of the sky,the first, of itskind in the world. Thus a new branchof astronomy was opened, known asRadio Astronomy.

OTHER ASTRONOMIESSatellite technology took astro-

nomical investigations farther afield inthe sixties. Untill then astronomicalstudies were entirely ground based.Now satellites made it possible tostudy astral phenomena from abovethe atmosphere. Thus astronomy isstudied from two levels, from theground and from above the atmo-sphere. This has led to the emer-gence of many specialised fields inastronomy, like–x-rays, Ultraviolet,Gamma ray and Infra-red rayastronomy.

ULTRAVIOLET ASTRONOMY

Ultraviolet astronomy is confinedto wavelengths between 912A andabout 3000 A. The first successfulobservation in the ultraviolet region ofthe spectrum was made in 1946,when the Naval Research Laboratory,USA, flew a captured German V-2rocket. The first successful dectectionof far ultraviolt radiation outside thesolar system was also made by theNaval Research Laboratory in 1955with the help of an AEROBEE 25rocket. Ultraviolet astronomy isspecially useful in very cases whereother techniques have failed to bringin any worthwhile information. Thusthere are many young massive starswith effective surface temperature of10,000 K which emit mostly in theultraviolet region. These stars can be

Geography/10

properly studied by UltravioletAstronomy Only.

GAMMA RAY ASTRONOMY

Gamma rays have the shortestwavelengths and are the mostenergetic rays so far known. Becauseof their great penetrating power, theyare not absorbed by the inter-stellarmatter and therefore reach us almost

ASTRONOMICAL TERMSTHE CELESTIAL SPHERE is an imaginary sphere upon

the surface of which all the stars in the sky appear to bestudded to an observer stationed at its centre.

THE ZENITH is the intersection of a vertical line throughthe observer’s station with the upper portion of the celestialsphere. It is the point on the celestial sphere immediately abovethe observer’s station.

THE NADIR is the intersection of a vertical line through theobserver’s station with the lower portion of the celestial sphere.It is the point on the celestial sphere vertically below theobserver’s stations.

THE CELESTIAL HORIZON (also called TRUE or RATIONALHORIZON) is the great circle in which a plane at right angles tothe Zenith and Nadir line and passing through the centre of theearth intersects the celestial sphere. The Zenith and Nadir arethe poles of the celestial horizon.

THE SENSIBLE HORIZON is the circle in which a planetangent to the earth’s surface (or at right angles to the Zenithand Nadir line) and passing through the point of observationintersects the celestial sphere. The line of sight of an accuratelylevelled telescope lies in this plane.

THE VISIBLE HORIZON is the circle of contact of the earth andthe cone of visual rays passing through the point of observation.

THE TERRESTRIAL EQUATOR (or simply, EQUATOR) is thegreat circle of the earth, the plane of which is perpendicular tothe axis of rotation (polar axis).

THE POLAR AXIS is the diameter about which the earth spins.The extremities of the axis of rotation (polar axis) of the earth,are known as the poles. they are distinguished as the NORTHPOLE and the SOUTH POLE.

THE CELESTIAL EQUATOR is the great circle in which theplane of the equator cuts the celestial sphere.

THE CELESTIAL POLES are the points of intersection of theaxis of the earth (or the polar axis) when produced with thecelestial sphere.

THE CELESTIAL MERIDIAN is the great circle in which theplane passing through the celestial poles intersects the celestialsphere.

THE MERIDIAN of a place or an observer is the great circlepassing through the zenith, and nadir and the poles.

THE ECLIPTIC is the great circle which the sun appears totrace on the celestial sphere with the earth as a centre in thecourse of a year. The plane of the ectiptic is not coincident withthe plane of the equator, the angle between them being knownas the OBLIQUITY OF THE ECLIPTIC. Its value is about 23°27'.

The points of intersection of the ecliptic with the equatorare called the EQUINOCTIL POINTS. The point at which thesun’s declination changes from South to North (i.e. the sunpassing from South to North of the equator) is known as the

VERNAL EQUINOX or the FIRST POINT OF ARIES; while theother is called the AUTUMNAL EQUINOX or the FIRST POINTOF LIBRA. The Vernal Equinox marks the beginning of spring,while the Autumnal Equinox marks the commencement ofAUTUMN.

The points on the ecliptic at which the North or Southdeclination of the sun is maximum are known as theSOLSTICES.

The sun is at the Vernal Equinox on March 21, and itsdeclination and right ascension are each equal to zero. On June21 the sun is at the ecliptic at 90° from the first point of Aries,and, its declination is maximum and equals 23°27' No and itsright ascension is 6 hours (or 90°).

THE VERTICAL CIRCLE is the great circle passing through thezenith and nadir. The meridian of a place is, therefore, also avertical circle.

THE PRIME VERTICAL is the vertical circle which passesthrough the east and west points of the horizon. It is at rightangles to the meridian of the place.

THE LATITUDE of a place or station is the angular distancemeasured from the equator towards the nearer pole, along themeridian of the place. The latitude is the declination of thezenith.

THE CO-LATITUDE of a place is the angular distance from thezenith to the pole. It is the complement of the latitude, and is,therefore, equal to 90°–latitude.

THE LONGITUDE of a place is the angular measure of the arcof the equator between some primary meridian and the meridianof place.

THE ALTITUDE of a heavenly body is its angular distanceabove the horizon, measured on the vertical circle passingthrough the body.

THE CO-ALTITUDE also called the Zenth Distance, is theangular distance of a heavenly body from the Zenith. It is thecomplement of the altitude and equals 90°––latitude.

THE AZIMUTH of a heavenly body is the angle between theobserver’s meridian and the vertical circle passing through thebody.

THE DECLINATION of a heavenly body is its angular distancefrom the equator, measured along the meridian, generally calledthe declination circle, that is, the great circle passing throughthe body and the celestial poles.

THE CO-DECLINATION also termed as the Polar Distance, isthe angular distance of the heavenly body from the pole. It is thecomplement of the declination, and is equal to 90°–declination.

THE HOUR ANGLE of a heavenly body is the angle betweenthe observer’s meridian and the declination circle passingthrough the body.

THE RIGHT ASCENSION of a heavenly body is its equatorialangular distance measured eastward from the First Point ofAries.

unchanged from all parts of theUniverse.

Gamma ray astronomy was bornin 1968 with the discovery of veryhard gamma ray radiation from thecentral region of our galaxy, by ateam of scientists at the Massa-chusetts Institute of Technology,USA, who had flown a sophisticatedgamma ray detection on board the

Orbiting Solar Observatory–3 satellite.Subsquent observations on celestialhard gamma rays from experimentson the US Small Astronomy Satellite–2 and European COS–B satellite haveestablished gamma ray astronomy asan observational science.INFRA RED ASTRONOMY

Infra red astronomy is importantbecause it enables us to observe

Geography/11/2

objects at temperatures betweenabout 10 K and 2,000 K, whether theyare cool stars or dust cloud. In thesolar spectrum the region nearest tothe visible red is called “nearinfrared”. A portion of this nearinfrared can be detected with specialphotographic plates. Hence this partof the infrared is called the Photo-graphic Infrared. Higher wavelengthscan be detected by other methods.

RADAR ASTRONOMY

Radar Astronomy was born in1940, when a Hungarian PhysicistZoltan Bay sent out a beam of microwaves to the moon and detected thereturn echo. The basic principle issimple. Short pulses of highfrequency radio energy are aimed ata target, from which the pulses arereflected to the earth, where they arepicked up by a sensitive antennareceiver system. The time betweenthe transmission and reception ofradar pulses can be converted into ameasure of distance by the speed atwhich these radar pulses travel.

Since micro waves can rightly beconsidered a part of the electro-magnetic spectrum, the RadarAstronomy is really a part of radioastronomy.

In recent years, the radartechniques have substantially addedto the stock of our knowledge ofastronomy. The surface of Venus,for the example, is covered by a thicklayer of clouds against which ouroptical telescopes were quite help-less. But microwaves have piercedthrough the clouds and have soundedthe solid surface of Venus. The firstreadings showed a high mountainrange. Subsequent readings havehelped us to make a radar map of thesurface. Various bits of informationabout other planets have been andare still being collected by radarreadings.

SUPER TELESCOPE

A new generation of ‘Super Tele-scope’ is designed for mountaintopsaround the world ushered in a goldenage of astronomy by the earlynineties.

Behind the spurt in jumbotelescopes are several radical newideas on how to build them. Eversince the dedication of the 200 inch

(5·08 metre) Hale Telescope–still theworld’s premier optical device–atopCalifornia’s Mount Palomar in 1948,astronomers thought that they hadreached the technical and financiallimits of big–telescope construction.

THE WORLD OFSOUND

Radio Telescopes have openeda new world to the astronomer–A World of Sound, not of sight.The two worlds are fantasticallydifferent. THE MILKY WAY, forexample, is a river of light to the eyesbut it is a bissing mass to the ears.Radio Telescopes, in facts help us tolisten in to stars or galaxies that lie farbeyond the ken of the world’s largesttelescopes. Radio Telescopes alsoenable us to study astral phenomenawhich are within the range of ouroptical telescopes but which are notvisible owig to the haze of cosmicdust.

Sound is produced by thevibrations of an object or mechanismand transmitted in the from of waves—alternating increase and decreasein pressures. It radiates outwardthrough a material medium ofmolecules, more or less like theripples spreading out on water aftersome heavy object has been throwninto it.

Two elements of sound areimportant—(i) the PITCH or FRE-QUENCY, and (ii) INTENSITY orLOUDNESS.

(i) The PITCH or FREQUENCYrefers to the rate of vibration of thesound and is measured in HERTZ(Hz) units. The frequency of sound isdetermined by the number of timesthe vibrating waves undulate persecond. The slower the cycle thelower the pitch. The pitch becomeshigher as the cycles increase innumber or which is the same thing, asfrequencies increase.

(ii) The INTENSITY or LOUD-NESS is measured in Decibels. Adecibel (db) (one-tenth of a “Bel”) isa physical unit based on the weakestsound that can be detected by thehuman ear. It is named after A. G.BELL, the inventor of the telephone.

The decibel scale is logarithmic,that is, an increase of 10 db means

10 times as much, an increase of 20db means 100 times and 30 db 1000times etc. A light whisper may beabout 10 db, a quite conversationsound 20 db, and normal talk 30 db.In comparison the electricallyamplified beat music in a disco is abillion times louder than the sound ofa whisper at 10 db.

ULTRA–SONICS

The human ear cannot generallybear sounds of frequencies higherthan 20,000 vibrations per second orin modren International Units 20,000Hz. Sounds of frequencies higherthan 20,000 Hz which are inaudibleare called ULTRA SONIC. Batsproduce very high sound when theyfly but they are at ultra-sonicfrequencies from 20,000 to 100,000Hz. So we cannot bear them. Ultra-sonic waves are an important tool ofresearch in physics. There are alsomany applied uses for ultra-sonicwaves, like “Submarine echo sound-ing’, ‘detection of flaws in casting’,‘drilling glasses and ceramic’,‘emulsification’ etc.

SPEED OF SOUND

The speed of sound variesaccording to the nature of the carriermedia. When we speak of speed ofsound, we ordinarily mean the speedat which sound travels in air at sealevel. This is around 1088 feet persecond. In water sound travels about5 times faster than in air. In iron andsteel it is even faster, about 3 timesfaster than the speed of water.Speeds of sound through someselected media are indicated below :

● Ice-cold water-1505 metre (4938feet) per second

● Brick–3542 metre (11620 feet)per second

● Granite–395 metre (1296 feet)per second

● Hardwood–3847 metre (12620feet) per second

● Glass–5000 to 6000 metre(16410 to 19690 feet) per second

SUPER–SONICS

Supersonic speed is speedgreater than the speed of sound (inair at sea level), that is to say, around760 miles or 1216 kilometres perhour. Supersonic speed is measuredin ‘MACH”. This unit was worked outby the Czech–born German physicist

Pratiyogita Darpan Extra Issue Series-2General Studies Geography (India And

World)

Publisher : Upkar Prakashan Author : Pratiyogita Darpan

Type the URL : http://www.kopykitab.com/product/8953

Get this eBook

30%OFF