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  1. 1. Chapter 6_1: Geo6_1_The Earth in the Solar SystemThe sun, the moon and all those objects shining in the night sky are called celestial bodies. These celestial bodies are called stars. The sun is a star. Various patterns formed by different groups of stars. These are called constellations.Ursa Major or Big Bear is one such constellation. One of the most easily recognisable constellationsis the small bear or Saptarishi (Sapta-seven, rishi-sages). It is a group of seven stars that forms a partof the large Ursa Major Constellation.In ancient times, people used to determine directions during the night with the help of stars. TheNorth Star indicates the north direction. It is also called the Pole Star. It always remains in the same position in the sky. We can locate the position of the Pole Star with the help of the Saptarishi.Some celestial bodies do not have their own heat and light. They are lit by the light of the stars. Suchbodies are called planets. The word planet comes from the Greek word Planetai which meanswonderers.Jupiter, Saturn and Uranus have rings around them. These are belts of small debris. These rings maybe seen from the earth with the help of powerful telescopes.
  2. 2. THE SOLAR SYSTEMThe sun, nine planets, satellites and some other celestial bodies known as asteroids and meteoroidsform the solar system The sun is about 150 million km away from the earth There are nine planets in our solar system. In order of their distance from the sun, they are:Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and PlutoMY VERY EFFICIENT MOTHER JUST SHOWED US NINE PLANETS.Aryabhata was a famous astronomer of ancient India.All the nine planets of the solar system move around the sun in fixed paths. These paths areelongated. They are called orbits. Mercury is nearest to the sun. It takes only about 88 days to complete one round along itsorbit. Pluto is supposed to be farthest till now. So it takes about 248 years to complete oneround. Venus is considered as Earths-twin because its size and shape are very much similar to thatof the earth. A new planet 2003 UB313 has been discovered recently in our solar system. It is bigger thanPluto and farthest from the Sun. Light travels at the speed of about 300,000 km per second. Yet, even with this speed, thelight of the sun takes about eight minutes to reach the earth. Our earth has only one satellite, that is, the moon. It is about 3, 84, 400 km away from us. Neil Armstrong was the first man to step on the surface of the moon on 29 July 1969. Human-made Satellite is an artificial body. Some of the Indian satellites in space are INSAT,IRS, EDUSAT, etc.Scientists are of the view that asteroids are parts of a planet which exploded many years back. Thesebodies are called asteroids. They are found between the orbits of Mars and Jupiter. The largestasteroid is the Ceres.The small pieces of rocks which move around the sun are called meteoroids. Sometimes thesemeteoroids come near the earth and tend to drop upon it. Like a white glowing path across the sky on a clear starry night, it is a cluster of millions ofstars. This band is the Milky Way galaxy. Our solar system is a part of this galaxy. In ancient India, it was imagined to be a river of light flowing in the sky. Thus, it was namedAkash Ganga. A galaxy is a huge system of billions of stars, and clouds of dust and gases.There are millions of such galaxies that make the Universe.
  3. 3. Chapter11_2: Geo11_2_The Origin and Evolution of the EarthOne of the earlier and popular arguments was by German philosopher Immanuel Kant.Mathematician Laplace revised it in 1796. It is known as Nebular Hypothesis. Later in 1900, Chamberlain and Moulton considered that a wandering star approached thesun. As a result, a cigar-shaped extension of material was separated from the solar surface. Sir James Jeans and later Sir Harold Jeffrey supported this argument. These arguments arecalled binary theories.In 1950, Otto Schmidt in Russia and Carl Weizascar in Germany somewhat revised the nebularhypothesis, though differing in details.Modern TheoriesThe most popular argument regarding the origin of the universe is the Big Bang Theory. It is alsocalled expanding universe hypothesis. Edwin Hubble, in 1920, provided evidence that the universe isexpanding.The Big Bang Theory considers the following stages in the development of the universe. In the beginning, all matter forming the universe existed in one place in the form of a ti nyball (singular atom) with an unimaginably small volume, infinite temperature and infinitedensity. At the Big Bang the tiny ball exploded violently. This led to a huge expansion. It is nowgenerally accepted that the event of big bang took place 13.7 billion years before thepresent. The expansion continues even to the present day. As it grew, some energy wasconverted into matter. There was particularly rapid expansion within fractions of a secondafter the bang. Thereafter, the expansion has slowed down. Within first three minutes fromthe Big Bang event, the first atom began to form. Within 300,000 years from the Big Bang, temperature dropped to 4,500 K and gave rise toatomic matter. The universe became transparentThe expansion of universe means increase in space between the galaxies.An alternative to this was Hoyles concept of steady state. It considered the universe to be roughlythe same at any point of time.
  4. 4. The Star Formation A galaxy contains a large number of stars. Galaxies spread over vast distances that aremeasured in thousands of light-years. The diameters of individual galaxies range from 80,000-150,000 light years. A galaxy starts toform by accumulation of hydrogen gas in the form of a very large cloud called nebula. Eventually, growing nebula develops localised clumps of gas. The formation of stars is believed to have taken place some 5-6 billion years ago A light year is a measure of distance and not of time. Light travels at a speed of 300,000km/second. Considering this, the distances the light will travel in one year is taken to be onelight year. This equals to 9.46110 12km. The mean distance between the sun and the earthis 149,598,000 km. In terms of light years, it is 8.311 minutes of a year.Formation of Planets Our Solar system consists of nine planets. The tenth planet 2003 UB 313 has also beenrecently sighted. The nebula, from which our Solar system is supposed to have been formed, started itscollapse and core formation some time 5-5.6 billion years ago and the planets were formedabout 4.6 billion years ago. Our solar system consists of the sun (the star), 9 planets, 63 moons, millions of smallerbodies like asteroids and comets and huge quantity of dust-grains and gases. Out of the nine planets, mercury, Venus, earth and mars are called as the inner planets asthey lay between the sun and the belt of asteroids the other five planets are called the outerplanets. Alternatively, the first four are called Terrestrial, meaning earth-like as they are made up ofrock and metals, and have relatively high densities. The rest five are called Jovian or Gas Giant planets. Jovian means jupiter-like.The difference between terrestrial and Jovian planets can be attributed to the following conditions:o The terrestrial planets were formed in the close vicinity of the parent star where itwas too warm for gases to condense to solid particles. Jovian planets were formedat quite a distant location.o The solar wind was most intense nearer the sun; so, it blew off lots of gas and dustfrom the terrestrial planets. The solar winds were not all that intense to causesimilar removal of gases from the Jovian planets.o The terrestrial planets are smaller and their lower gravity could not hold theescaping gasesIn 1838, Sir George Darwin suggested that initially, the earth and the moon formed a single rapidlyrotating body.EVOLUTION OF THE EARTHThe planet earth initially was a barren, rocky and hot object with a thin atmosphere of hydroge n andhelium
  5. 5. Development of Lithosphere The earth was mostly in a volatile state during its primordial stage. Due to gradual increasein density the temperature inside has increased. With passage of time it cooled further and solidified and condensed into a smaller size. This later led to the development of the outer surface in the form of a crust During the formation of the moon, due to the giant impact, the earth was further heated up.Evolution of Atmosphere and Hydrosphere The present composition of earths atmosphere is chiefly contributed by nitrogen andoxygen. There are three stages in the evolution of the present atmosphere.o The first stage is marked by the loss of primordial atmosphere.o In the second stage, the hot interior of the earth contributed to the evolution of theatmosphere.o Finally, the composition of the atmosphere was modified by the living world throughthe process of photosynthesis The early atmosphere, with hydrogen and helium, is supposed to have been stripped off as aresult of the solar winds. The early atmosphere largely contained water vapor, nitrogen, carbon dioxide, methane,ammonia and very little of free oxygen. The process through which the gases wereoutpoured from the interior is called degassing.
  6. 6. Chapter 8_17: Sci8_17_Stars And The solar system The objects which do not twinkle are planets. The moon is the brightest object in the night sky. The stars, the planets, the moon and manyother objects in the sky are called celestial objects The various shapes of the bright part of the moon as seen during a month are called phasesof the moon The time period between one full moon to the next full moon is slightly longer than 29 days. The moon completes one rotation on its axis as it completes one revolution around theEarth. On July 21, 1969 (Indian time) the American astronaut Neil Armstrong landed on the moonfor the first time followed by Edwin AldrinThe Sun is nearly 150,000,000 kilometers (150 million