UPSC Prelims 2024 Geography Quick Revision Module PDF

QUICK REVISION MODULE (UPSC PRELIMS 2024) GEOGRAPHY UNIVERSE AND SOLAR SYSTEM  THE UNIVERSE: THE VAST SPACE SURROUNDING US IS CALLED UNIVERSE. IT IS MOSTLY EMPTY SPACE. ORIGIN OF THE UNIVERSE BIG BANG THEORY OR EXPANDING UNIVERSE HYPOTHESIS It was g...

QUICK REVISION MODULE (UPSC PRELIMS 2024) GEOGRAPHY UNIVERSE AND SOLAR SYSTEM  THE UNIVERSE: THE VAST SPACE SURROUNDING US IS CALLED UNIVERSE. IT IS MOSTLY EMPTY SPACE. ORIGIN OF THE UNIVERSE BIG BANG THEORY OR EXPANDING UNIVERSE HYPOTHESIS It was given by Edwin Hubble. In the beginning, universe was a tiny ball (single atom) with unimaginably small volume and infinite temperature and density. 13.7 billion years ago, this ball exploded leading to a huge expansion. This expansion is continuing until now, at a smaller pace. First atom began to form within 3 minutes of Big Bang. Within 300,000 years of explosion, temperature dropped to 4500 K and gave rise to atomic matter. Universe became transparent. The expansion in universe means increase in space between the galaxies. An alternative theory is ‘Hoyle’s concept of steady state’ which considers universe to be roughly of same size at any point of time. The Stars: They are the heavenly bodies like the sun that are extremely hot and have light of their own. Stars are made up of vast clouds of hydrogen gas, some helium and dust. Galaxies: They are building blocks of the universe. Galaxy is a vast system of billions of stars, which also contains a large number of gas clouds mainly of hydrogen gas (where stars are born), and dust, isolated in space from similar system. www.visionias.in Vision IAS 1  NEBULAR HYPOTHESIS A galaxy starts to form by accumulation of Hydrogen gas in the form of a very large cloud called Nebula. This growing Nebula starts developing localized clumps of gas. These clumps continue to grow into even denser gaseous bodies, giving rise to formation of star. This event took place 5 to 6 billion years ago. STELLAR EVOLUTION LOW AND MEDIUM-MASS STARS (INCLUDING THE SUN) White Main “Planetary” dwarf Sequence Red giant nebula High-mass High-mass star Nebula stars Neutron star Main Sequence Red supergiant Supernova Very high-mass Black star hole www.visionias.in Vision IAS 2  BIRTH AND EVOLUTION OF A STAR In the beginning, Galaxy had just very cold (-1730C), dense and large cloud of gases (Hydrogen and Helium). Very large gravi- tational pull led to the formation of a highly condensed body PROTOSTAR called Protostar. A protostar is a huge, dark, ball of gases. It does not emit light. Further contraction of Protostar leads to collision of Hydrogen gases and increases the temperature of the protostar from -1730 C to 107 0C. Hence, fusion reaction, where 4 Hydrogen STAR nuclei fuse to form Helium and release tremendous amount of energy in the form of heat and light. It makes the star shine. Fusion reaction stops in the core when its Hydrogen gets ex- hausted. Pressure of the core diminishes and core starts shri- nking. Fusion takes place as some Hydrogen remains in the envelope/outer shell. It makes the star unstable. The star Ex- RED STAR pands and turns Red. Sun will enter its Red giant phase in 5000 million years from now. Its expanding outer shell at the time will engulf inner planets i.e. Mercury Venus and Earth. When mass of star < 1.44 times the mass of Sun (Chandra Shekhar limit), it ends up as a white dwarf. The Red Giant Star looses its outer envelop and core shrinks DWARF into an extremely dense ball of matter due to gravitation. This STAR leads to another set of fusion reaction where Helium fuses to form carbon. The fuel gets completely exhausted and the core shrinks under its own weight and becomes a white dwarf. www.visionias.in Vision IAS 3  When mass of star > 1.44 times that of Sun, there remains enough Helium in the core for fusion reaction. The outer envelope explodes causing Supernova Explosion. When mass of the star is between 1.44 to 3 times that of Sun, SUPERNOVA it becomes a Neutron Star When mass of the star is bigger than 3 times that of Sun, it becomes a Black hole. THE SOLAR SYSTEM: Sun is a ball of hot gases, Loop mainly Hydrogen. THE SUN 6000o Prominence Chromosphere Sun spots Shining surface of the Spicules 1.5 Mo Sun is called Photosphere. Radiative Coronal High Zone 15 M o Temp- The outer layer of the Convection Zone erature 2 million sun’s atmosphere is made Core Degress up of thin hot gases is Photosphere called Corona. Coronal hole Corona is visible only High speed during full eclipse. Solar wind GOLDILOCKS ZONE: A habitable zone, also called a Goldilocks zone, is the region around a star where orbiting planets similar to the Earth can support liquid water. It is neither too hot, nor too cold. www.visionias.in Vision IAS 4  PLANETS Planets are solid heavenly bodies which revolve round a star (e.g. the sun) in closed elliptical paths. A planet is made of rock and metal. It has no light of its own. A planet shines because it reflects the light of the sun. The planets move round the sun from west to east, so the relative positions of the planets keep changing day by day. There are 8 major planets including the earth.. The jovian planets The terrestrial planets Jupiter Saturn Uranus Naptune Pluto Mercury Venus Earth Mars CASE OF PLUTO: As per International Astronomical Unit, three given characteristics are required to qualify as a planet: 1 The celestial body has to be in orbit of the Sun 2 It must have sufficient mass to assume hydrostatic equilibrium (i.e. a nearly round shape), and 3 It must have ‘cleared the neighbourhood’ around its orbit i.e. it must become the dominant gravitational body in their orbit. Pluto lacks the third charac- teristic. That’s why it is not a planet anymore and has been categorized as a Dwarf Planet. www.visionias.in Vision IAS 5  TWO GROUPS OF PLANETS: TERRESTRIAL VS JOVIAN TERRESTRIAL PLANETS JOVIAN PLANETS (EARTH LIKE) ( JUPITER LIKE) Four innermost planets i.e. Mercury, Includes Jupiter, Saturn, Uranus, and Ne- Venus, Earth, and Mars ptune are known as the Jovian (Jupiter- like) planets, because they are all gigantic compared with Earth, and they have a They have a compact, rocky surface like gaseous nature like Jupiter's -- mostly Earth's terra firma. hydrogen, with some helium and trace gases and ices. None of the terrestrial planets have rings, although Earth does have belts Also referred to as the "gas giants". of trapped radiation. All of them have significant planetary Among the terrestrials, only Earth has magnetic fields, rings, and lots of satellites. a substantial planetary magnetic field. Mars and the Earth's moon have local- Jupiter is more massive than all the other ized regional magnetic fields at differ- planets combined. It emits electromag- ent places across their surfaces, but no netic energy from charged atomic part- global field. icles spiraling through its strong magn- etic field. Of the terrestrial planets, Venus, Earth, and Mars have significant atmospheres. Saturn, the farthest planet easily visible to the unaided eye, is known for its ex- tensive, complex system of rings. Its Mercury lacks an atmosphere. Even moon Titan is the second largest moon though most of its surface is very hot, after Ganymede (Jupiter’s moon). there is strong evidence that water ice exists in locations near its north and Among four Galilean satellites of Jupiter: south poles which are kept permane- Lo is the most volcanically active body in the solar ntly shaded by crater walls. system, due to heat resulting from tidal forces. Europa is covered with an extremely smooth shell of water ice. There is probably an ocean of liquid Venus' atmosphere of carbon dioxide water below the shell. is dense, hot, and permanently cloudy, Ganymede has mountains, valleys, craters, and making the planet's surface invisible. cooled lava flows. Its ancient surface resembles Earth's moon, and it is also suspected of having a sub-surface ocean. Mars' atmosphere, also carbon dioxide, Callisto, the outermost Galilean moon, is pocked is much thinner than Earth’s. Mars has all over with impact craters, indicating that its polar caps of carbon dioxide ice and surface has changed little since the early days of water ice. its formation. www.visionias.in Vision IAS 6  Together, they have just 3 moons (1 Saturn, Uranus and Neptune all have rings of Earth and 2 of Mars). made up of myriad particles of ice ranging in size from dust and sand to boulders. SATELLITES: A satellite (or moon) is a solid heavenly body that revolves round a planet. Except Mercury and Venus all other planets of solar system have satellites. The satellites have no light of their own. They shine because they reflect the light of the sun. - Jupiter has the largest number of Moons. It also has the biggest moon of the solar system, Ganymede. - Saturn’s moon ‘Titan’ has its own atmosphere. ABOUT EARTH’S MOON It is a natural satellite of Earth. It revolves around the Earth in a definite regular path. Gravitational attraction of the earth holds the moon into its orbit. It is about 1/4th size of the Earth in diameter and 1/8th in weight. Moon does not have air or water. Its surface is covered with hard and loose dirt, craters and mountains. Days are extremely hot and nights are very cold on moon. THEORIES OF FORMATION OF MOON: 1. DARWIN: 2. MATERIALFORMING 3. GIANT IMPACT OR THE BIG Both earth and moon The moon was separ- SPLAT: formed a single rapidly ated from what we have A body of the size of one to rotating body. The whole at present the depress- three times that of Mars coll- mass became dumb-bell ion occupied by Pacific ided into the earth shortly shaped and eventually ocean. after the earth was formed. broke. It blasted a large part of earth into the space. The blasted portion started re- volving around the earth and eventually formed into the present moon after 4.4 million years ago. Most accepted theory. www.visionias.in Vision IAS 7  OTHER OBJECTS IN THE SKY: ASTEROIDS Asteroids are a belt of debris composed of rock and metals, which somehow failed to assemble into a planet and keep revolving between the orbits of Mars and Jupiter. There are as many as 100,000 asteroids. The biggest aste- roid called ‘Ceres’ has a diameter of about 800 km whereas the smallest asteroid is of size of a pebble. Asteroids can collide with earth. It is believed that the exti- nction of dinosaur was due to such a collision. The Lonar Lake in Maharashtra is a filled up crater formed after an as- teroid collision. COMETS They are celestial objects formed of ice and dust. They were formed very early from the same gas clouds from which other members of the solar system are formed. They orbit the Sun. When their normal path gets disturbed, they start moving towards the sun. As the comet approac- hes Sun, the ice sublimates into gas and form along with the entrained dust particle, a bright outflowing atmosphere around the comet nucleus called Coma. The comet may also form two tails, one of ionized molecules and radicals and other of dust. The tails of the comet always point away from the Sun. The study of the tails of the comet has shown presence of Car- bon, Hydrogen, Nitrogen and Oxygen in it. Comets do not last forever. Whenever they come close to sun, their gases get over and ultimately only dust particles remain. They are small celestial bodies (may include dust particles METEORS of a comet, or a piece of broken asteroid) which enter into the earth’s atmosphere and burns as a bright streak of light due to heat produced by the friction of its impact with the atmosphere. They are also called shooting stars. If a Meteor is big enough and does not gets burnt up comp- letely, and lands on earth (like stones from sky), it is called Meteorite. It should be noted that the number of meteorites on moon’s surface is much larger than that on earth because moon does not have an atmosphere to burn the meteor. Study of meteorites can reveal the nature of materials of which the solar system is composed of. www.visionias.in Vision IAS 8  THE EARTH’S MOVEMENT: The Earth, as the rest of the planets of 23o 5' the Solar System, rotates on its and Is the angle (rotation movement) and around the Sun between the Earth’s (Orbit movement). These two movements are axis and the Sun. MARCH 21st responsible for phenomena such as day and Spring equinox night and the sequence of the seasons. in the Northern hemisphere. Day and nigh hours ORBIT JUNE 21st are the same. The Earth takes 365 days. Summer solstice 5 hours and 48 minutes to in the Northern complete a burn around the hemisphere. It is Sun. As the Sun Varies its the longest day position relation as the Sun. of the year. The seasons appear and thee LEAP YEARS variation of the days and nights. Every four years February has 29 days instead of SEPTEMBER 21st 28 they are the Autumnal equinox in the leap years. Northern Hemisphere. Day and night have the same amount of hours. DECEMBER 21st JET LAG Winter solstice in the Northern Long distance trips on an airplane cause same well known disorders such as jet lag. hemisphere. It is the shortest day Since they alter the habitual schedules of of the year. the body. 24:00 GREENWICH HOURS MERIDIAN 21:00 3:00 TIME ZONES The Earth is divided in twenty four areas or time zones, each with a different time, with Greenwich Meridian as a central axis. As you areas a 18:00 N 6:00 meridian to the East, an hour is added, and when you cross it to the West, an hour is substracted. 15:00 9:00 12:00 HOURS ROTATION NORTHERN Rotation is thee HEMISPHERE turn that the HEMISPHERES earth does on The Earth is divided ROTATION into two halves; the its axis every day. AXIS northern hemisphere It is the responsible EQUADOR and southern hemis- movement for the phere. Equater is the succession of days imaginary line betw- and nights, of the een them. When it is flattening of the summer is the north, poles, the marine south is winter and currents and the vice versa. different time SOUTHERN zones. HEMISPHERE www.visionias.in Vision IAS 9  POSITION OF SUN OVERHEAD VERNAL EQUINOX Sun overhead at Equator SUMMER SOLSTICE WINTER SOLISTICE Sun overhead at Sun overhead at Tropic of cancer Tropic of Capricon AUTUMNAL EQUINOX Sun overhead at Equator ECLIPSE SOLAR LUNER ECLIPSE ECLIPSE DAY NIGHT NEW EARTH FULL MOON MOON www.visionias.in Vision IAS 10  ECLIPSE EARTH’S ORBIT PENUMBRA UMBRA SUN MOON TOTAL ECLIPSE EARTH PARTIAL ECLIPSE MOON’S ORBIT EARTH’S UMBRA ORBIT MOON EARTH SUN MOON’S ORBIT PENUMBRA FOR DETAILED ENQUIRY, PLEASE CALL: 11 Vision IAS www.visionias.in GUWAHATI