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THE UNIVERSE 9th Grade Physics 9th - Physics

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INTRODUCTION What do you see in the sky? What comprises of the solar system? The Sun The Moon The planets Mercury Venus Mars Jupiter Saturn Fainter planets Uranus Neptune Asteroids Ancients observed Positions of celestial bodies Attempted to describe the motion of celestial bodies 9th - Physics

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Constellations Ancients grouped stars into patterns Named the patterns based on the imagined familiar objects and mythical characters By Ptolmeys time 48 constellations have been known. By Gallileo Gallileis time 60 constellations were known. Today the sky is divided into 88 constellations Of these the 12 constellations lying in the ecliptic are the zodiacal constellations Constellations were used to define the positions of celestial objects Motion of planets is confined to a narrow belt of the zodiacal constellations Planetary motion is along the ecliptic plane. 9th - Physics

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Constellations Observing Moon and planets over a period of one week night after night, Moon displaced more towards East. When the planets do not even seem to shift at all. This is because Moon is very near to us, when compared to planets. Similar effect is seen when we observe an aero plane flying high. Aero plane appears to fly slower when compared to the birds. The nearer planets like Mercury and Venus show greater displacement than the farther planets Jupiter and Saturn. On the New moon day, Moon sets at the same time as the Sun, 15 days later Moon rises in the East, while the sun sets in the West. All these facts can be drawn by studying the positions against the backdrop of zodiacal constellations. 9th - Physics

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Constellations Constellations served as a fixed background against which the motion of the planets can be observed. Mars is in the constellation of scorpius or in Saggitarius indicates that Mars is in the direction of the particular constellation Mars is just located in that direction Planets are more nearer to Earth when compared to the distance of the stars of the constellations Moon, Mars and rest of the planets move in the eastward direction. This eastward direction is called Direct Motion. Direct motion of Earth is due to the rotation of the Earth. One can infer the motion as well as the direction of motion of celestial bodies, with the aid of constellations. 9th - Physics

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Models of Solar system Early Greek astronomers assumed that each planet went around the Earth in a small circle called Epicycle. The centre of the Epicycle also followed a circular path around the fixed Earth The model in which Earth remained fixed, and all the celestial bodies revolved around it is called Geocentric model of Ptolemy Planets Mercury and Venus are not visible throughout the night. Mercury can be seen for a maximum duration of two hours. Venus can be seen for about three hours. Geocentric theory explained this phenomenon by assuming that the planets Mercury and Venus went around the Earth in an orbit less than that of the Sun. 9th - Physics

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Helio Centric Theory Nicholas Copernicus (1473-1543) proposed a model in which the Sun was at the Centre while all the planets including the Earth moved around it. This theory is called Helio-centric (sun centred) theory. Whatever motion that appears in the sky is due to the motion of the Earth itself. Heliocentric theory easily explained why Mercury and Venus did not appear throughout the night. 9th - Physics

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Distance Measurement - AU When Mercury is at the largest separation from Sun, it makes 28 between the lines joining the Sun-Earth and Sun-Mercury. Sun-Mercury can be expressed in terms of Sun-Earth distance called Astronomical Unit(AU). 1AU ~ 150 Million Km. AU is often employed as the basic unit of distance among solar system objects Deductions of Copernicus on distance measurement match very well with the current calculations. Distance measurement is one of the key contributions of Helio centric theory. 9th - Physics PlanetDistance CopernicanModern Mercury0.39 Venus0.72 Earth1.00 Mars1.52 Jupiter5.225.20 Saturn9.079.54

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Laws of Planetary Motion Johannes kepler (1571-1630) perfected the Heliocentric theory and described the motion as well as orbit of planets. The orbit of Mars was unusually difficult. Kepler used the accurate observations of the positions made by Tyco Brahe. Kepler studied the motion of planets and stated three laws known as Keplers laws of planetary motion. First law states that the orbit of planets are elliptical. Second law refers to the period of the planet. Third law refers to the speed of the planet at different positions. 9th - Physics

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Mercury Not much was known about Mercury until space probes were launched in 1974 Mercury is small in size and is very close to the sun Its surface temperature varies greatly It sets within two hours of the sun setting or rises within two hours of the sun rising. Like Earth, Mercury has a rocky surface It has no atmosphere A striking feature of the planet Mercury is craters Mercury revolves fastest around the Earth By the time Sun moves from one high noon position to the next with respect to Mercury, six months would have elapsed on the Earth 9th - Physics

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Venus Venus is the brightest object in the sky next to the Moon Its orbit is twice as large as Mercurys. The planet is visible for a longer time than Mercury as much as three hours. Venus and the Earth have almost the same size and mass. Temperature on Venus remains a constant at 750K. A thick atmosphere of Carbon-di-oxide along with the Sulphuric acid vapour envelopes the planet This produces enormous pressure at the surface about 90 times on the surface of the Earth The thick cloud reflects nearly 75% of the light falling on it. This is the cause of brightness of Venus 9th - Physics Green house effect: Carbon di oxide is opaque to heat. That is all the heat generated within the planet is trapped. This causes the temperature of Venus to steadily increase. This phenomenon is known as Green house effect. A warning for what is in store for us if global warming continues.

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Mars Mars lies in an orbit larger than the Earth Seen all through the night as a brilliant red object. The axis of rotation is inclined at an angle of about 24 to its orbit. It experiences Seasons as Earth does. It has a very thin atmosphere mostly composed of Carbon-di-oxide It has two tiny moons called Phobos, meaning fear and Deimos meaning panic, that swiftly around Mars. 9th - Physics

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Asteroids Region between the orbits of Mars and Jupiter is composed of planetsimals that did not combine to form larger bodies like planets. They are small chunks of rocks and metal that orbit the Sun. Largest asteroid is known as Ceres which has a diameter of about 950 km. Asteroids are found to be between 2 and 3.5 AU from the Sun. This region is called Asteroid belt. 9th - Physics

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Jupiter Most massive Gaseous planet with a mass equal to that of 318 Earths The volume is nearly 1400 times that of the Earths. It accounts for 2/3 rds of all material outside the Sun in the solar system. Inspite of huge mass and volume, it rotates fastest among all the planets. Jupiter is chiefly composed of Helium and Hydrogen gases, Conditions in the interior of Jupiter make it less likely to harbour life. The inner temperature may be 13000K and 35000K. The pressure is million times that on the Earth Gallileo discovered 4 moons of Jupiter Lo, Callisto, Ganymede and Europa. Called as Gallilean Satellites. Gallilean satellites are the first celestial objects discovered through telescope. 9th - Physics

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Saturn Known for its beautiful rings Huge Gaseous planet Mainly made up of Hydrogen and Helium Its atmosphere is mostly made up of Methane, ammonia and water vapour Density of Saturn is less than that of water Since the planet is far away from the sun, it is very cold Saturns rings are composed of small, unconnected pieces of rock and dust. This nature of rings was predicted four decades before it was discovered. 9th - Physics The rings are tilted at an angle to the orbit of saturn. The orientation, therefore appears to change as seen from the Earth over one revolution of Saturn.

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Uranus First planet invisible to naked eye and first planet to be discovered by telescope. Discovered by William Herschel in 1781 Doubled the range of known solar system, Saturn is at the same distance from Sun as Uranus is from Saturn. It receives only 1/400 th of the solar energy we receive on the Earth, But Its temperature is not very low. Spacecraft Voyager does not reveal any evidence of life. By 19 th century, astronomers could precisely predict the position of Uranus This prediction was possible through Keplers laws of motion along with Newtons law of Gravitation. The laws are applicable well beyond the Earth, they are truly universal laws. 9th - Physics Rings of Uranus was discovered by Prof. J.C Bhattacharya and Kuppusamy of Indian Institute of Astrophysics

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Neptune & Great Pluto War Discovery of Neptune was entirely due to the application of Newtons laws of motion and gravitation. The fact that the laws govern the motion of bodies on the Earth could be extended to motion of bodies elsewhere in the solar system is a big leap in understanding the universe. Methane and Ammonia form the bulk of Neptunes composition. This is another very cold planet. 9th - Physics From the time of its discovery from 1930 until 2006, Pluto was considered as the ninth planet. Many objects similar to Pluto were discovered in the outer parts of solar system in late 20th and 21st centuries. The scattered disc like Eris is 20% more massive than Pluto. On August 24, 2006, the IAU defined planet for the first time. This definition excluded Pluto from planet hood and reclassified it under the new category of dwarf planet along with Eris and Ceres.

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Comets Comets are chiefly composed of water, carbon monoxide, carbon di oxide, methane, ammonia and hydrogen cyanide all in frozen state When comets are well beyond the orbit of Jupiter, they are visible as dim objects only through powerful telescopes. As they come closer to Sun, they grow brighter. All comets do not become bright enough to be visible to naked eyes. Some comets like Comet Halley is very bright. As comets approach Sun, their frozen gases gradually vaporize. The energetic particles produced by the Sun, pushes the gas away from the Sun, leading to the formation of tail. The length of the tail increases as the comet approaches the sun. And decreases as the comet goes away from the sun. The amount of Suns heat reaching the comet as well as the mass of the gaseous material in it decide the length of the tail. Keplers laws are used to predict the positions of a comet during its journey. Using this it can even be concluded that the comet is being observed for the first time or it had been observed in the past. 9th - Physics

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Planetary data 9th - Physics PlanetMean dist (AU) Diameter (m) Mass (Kg) Range of Surface Temp(K) Mercury0.39100 to 623 Venus0.72750 Earth1.00183 x 333 Mars1.52133 to 293 Jupiter5.20163 Saturn9.5493 Uranus19.1957 Neptune30.0657

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Structure of Earth The earths structure is classified as below Crust Mantle Core Outer Core Inner core

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Structure of Earth - Crust The part of earth where we stand is called Crust It is about 30-40 km in thickness and is the outermost layer It is composed of rocks and is also known as Lithosphere (Lithos means rocks) The rocks are made of chemical compounds such as oxygen and silicon It contains needed nutrients for the growth and development of plants The crust provides food and shelter to thousands of organism like earthworm, ants, termites.. Finally as you know, it holds up lot of water that comes down as rain which is important as far as life on earth is concerned Al Aluminum Fe Iron Ca Calcium Na Sodium Mg Magnesium K Potassium T Titanium H - Hydrogen

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Structure of Earth - Mantle Mantle is the portion of the earth below the crust It is about 2900 km in thickness It is composed of silicates of iron and magnesium As crust is not deep, study of features like composition, temperature and pressure is possible using measuring instruments, while study of mantle needs to be done by indirect means as it is too deep Hence study of mantle is done by studying the vibrations caused by earth

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Fact file Spiders are scientists tool Spiders weave a web and wait for their prey As soon as they fly gets stuck, the spider feels the vibrations The vibrations reach the spider from various directions Spider analyzes the strength of vibration to find the position and possibly the size of prey Hence, vibrations can be used to detect objects and also to infer the nature of the object The same principle is used by humans to understand the mantle through earth quake vibrations

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Structure of Earth - Core Core is the portion of the earth below the mantle Its radius is about 3470 km, about half the size of earth Temperature of core is about 4000 kelvin while the pressure is very high Magnetic compass always aligns in north-south direction any idea why is it so? Until 1600 AD this was believed to be caused by a pole star, but Sir William Gilbert explained that the alignment was due to earth behaving as giant magnetic field Now, how does the earth behave as giant magnetic field? The magnetic field is due to the motion of molten iron at the core and this motion is caused by- Rotation of the earth as well as the convection currents due to heat of molten iron

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Atmosphere Atmosphere stretches of about few hundred kilometers. For living process, up to a height 50 km is essential Atmosphere composition: Major components includes nitrogen and oxygen Nitrogen is key ingredient of amino acids Nitrogen is also essential for plants But, plants cannot take nitrogen directly, so Bacteria on earths crust helps plants to take nitrogen. They are known as nitrogen-fixing bacteria Water vapor in the atmosphere is the third component in the atmosphere important for weather conditions

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Layers of Atmosphere - Troposphere Atmosphere is classified into different layers based on temperature and composition TROPOSPHERE (tropos means heat) The layer nearest to the crust is the troposphere It extends to a height of 11 km 75% of air molecules that make up the atmosphere are found in troposphere Oxygen and nitrogen the key elements of living organisms survival float around in troposphere Troposphere is also important in deciding the weather conditions, i.e fog, haze, rain

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Layers of Atmosphere - Stratosphere The layer above the troposphere is the stratosphere It extends to a height of 40 km from troposphere It contains Ozone (an allotrope of oxygen). Molecule of Oxygen is made of two atoms of oxygen but ozone contains three atoms of oxygen (O3) Concentration of ozone is very less ~ one molecule in four million Ozone plays an important role is absorbing the harmful ultra-violet (UV) rays present in sunlight Life on earth survives as Ozone acts as a shield from UV radiation

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Layers of Atmosphere - Hydrosphere 2/3 rd of earths surface is water Water is the only liquid that exists in three state of matter on earth As frozen ice caps, in ocean and as water vapor in atmosphere Living organisms in oceans gradually increased the content of oxygen in the atmosphere by biological process known as photo synthesis With the production of oxygen came ozone and hence the emergence of life on earth So, even hydrosphere influences the composition of the atmosphere and in turn the life on land

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Layers of Atmosphere Weather (Convection Current) A known fact - Earth receives heat and light from Sun Air molecules on earth gets heated up when the come in contact with heated land surface Hot air is less dense than cold air So hot air rises up and gradually gets cooled Meanwhile, the cold air that displaces the hot air gets heated up Now this heated up air rises up. This phenomenon, where hot air rises up and cold air coming down set up the convection current Fact File This is the same principle seen in boiling of water Hence, as heat energy is transported using the air in atmosphere, the atmosphere acts as a heat distribution system

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Layers of Atmosphere Weather (Water Cycle) Water in the earth also plays an important role in heat energy distribution As we already know, water covers 2/3 rd of earths surface Water in lakes, seas and ocean vaporize slowly due to the suns heat But, as water has a high specific heat, hence, lot of heat energy is needed for water to vaporize The water vapor that rises in the atmosphere, stays there in the atmosphere and forms clouds with dust particles When the clouds condense and cool, water vapor changes to liquid form and comes down as rain. This is how we get rainfall on earth This phenomenon is called the Water Cylce The processes Convection Current and the Water cycle ensures pleasant weather conditions on earth

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Layers of Atmosphere Weather The processes Convection Current and the Water cycle help matter to move in vertical direction only This would not be much help in distributing heat energy across the globe The earths rotation ensures that the moving air is deflected from its vertical path As the air rises up vertically, it is subjected to a sideward force due to earths rotation Hence, the air rises up and moves side wards resulting in distribution of heat energy over larger surface area of the earth

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Fact File - Water Water is a wonderful and much needed compound to sustain life on earth Nearly 70% of the cell is water Water dissolves a number of compounds like Carbon di-oxide and oxygen and salts in the body Water is essential for blood circulation Force of attraction among molecules of water aids capillary action, this helps plants to reach leaves Carbon di-oxide and water combine to produce carbohydrate As water freezes, its volume increases, and because of this ice floats on water This unique property helps the cells on seas and oceans to survive

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Earth as a dynamic system Earth appears static, But the truth is that Earth is working actively all the time. It receives energy from the Sun, drives convection current in the atmosphere, sets up water cycle process all the time. It rotates continuously and distributes the water and air molecules and energy all over the planet. Earth is very much like a living system. A living system has several individual parts. The individual parts cannot exclusively constitute a system. The basic factor is co-ordination. Earth co-ordinates among all its individual components - living as well as non-living. 9th - Physics