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# Module 2 Universe

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### Module 2 Universe

1. 1. THE ME: THE UNIVERSE/ ASTRONOMY STARS If you look into the sky at night, you’ll see that stars look like points of light. You will probably also notice that some stars are brighter than others. If you look closely, you’ll see that some stars have different colors. However, you can’t tell how large or how far away a star is simply by looking at it. You can’t poke the sun, which is considered to be a fairly average star. DISTANCES TO THE STARS Although the sky seems full of stars, most of the universe is nearly empty space. The seeming contradiction exist because most stars are separated by vast distances. The Light-Year ; you wouldn’t measure the distances between two distance cities in centimeters. Similarly, because stars are so far apart, it’s not practical to measure their distances in units that might be used on Earth, such as kilometers. Instead, astronomers use much larger units, including the light- year is the distance that light travels in a vacuum in a year, which is about 9.5 trillion kilometers. Proxima Centauri, the closest star to the sun, is about 4.3 light-years away. Parallax; Stars are so far away that astronomers cannot measure their distance directly. Astronomers have developed various methods of determining their distances to stars. Different methods are used for stars at different distances. To understand how astronomers can measure distances to nearby stars, hold your thumb up at arm’s length in front of you. Close your left eye and look at your thumb with just your right eye open. Then cover your right eye and look with just your left eye open. Even though you didn’t move your thumb, it appeared to move relative to the background because you look at it from slightly different angles. The apparent change in position of an object with respect to a distance background is called parallax. As earth moves in its orbit, astronomers are able to observe stars from two different positions. Imagine looking at the stars in winter and then six months later in summer. During this time, Earth has moved from one side of its orbit to the other-a distance of a distance of about 300 million kilometers. Because people on Earth is looking from a different angle, the nearby star appears to move against the more-distant background stars. Before the invention of the telescope, astronomers couldn’t measure a star’s position very accurately. They couldn’t detect the apparent movement of a single nearby star as Earth moved around the sun. With the invention of the telescope, astronomers could measure the position of stars with much greater accuracy .Astronomers measure the parallax of nearby stars to determine their distance
2. 2. from Earth. The closer a star to Earth, the greater is its parallax. Astronomers have measured the parallax of nearby stars and determine their distances from earth. However, if a star is too far away, its parallax is too small to be measured. With present technology, the parallax method gives reasonable accurate distance measurements for stars within a few hundred light-years. Astronomers have developed other ways to estimate distances to more-distance stars. PROPERTIES OF STARS There are many types of different stars. Astronomers classify stars by their color, size, and brightness. Other important properties of stars include their chemical composition and mass. Colour and Temperature: Have you ever looked closely at a candle flame? The hottest part of the flame near the wick is blue or white, while the cooler flame tip is orange. A propane torch flame is blue. Dying campfire embers are red. You can estimate the temperature of a flame from its color. In the same way, a star’s color indicates the temperature of its surface. The hottest stars, with surface temperature above 30, 000 k, appear blue. The surfaces (photosphere) of relatively cool are red stars are still toasty 3000 k or so. Star with surface temperature between 5000 and 6000 k appear yellow, like the sun. The differences between hot blue stars and cool red stars can be seen with the unaided eye. More precise measurement of stars’ temperatures can be made by studying stars’ spectra. Brightness ;When you walk along a street at night, look up at a row of street lights. The closer lights the closer lights look bright and the more distant lights look dim. However, the more distant lights are not really dimmer. They appear dim to you because at greater distance, their light is spread out over a greater area, so a smaller portion enters your eyes. The same is true for the light emitted by stars. You might think that closer stars will always appear brighter than more distant stars. Astronomers have discovered, however, that the brightness of stars can vary by a factor of more than a billion. So, stars that look bright may actually be farther away than stars that appear dim . Although the sun appears to be the brightest star in our sky, it is really a star of only average brightness. The sun appears very bright to us because it is much closer than other stars. The brightness of a star as it appears from Earth is called its apparent brightness. The apparent brightness of a star decreases as its distance from you increases. If you move away from a street light or a star, it shines just a brightly as before-but to you it appears fainter. Absolute brightness is how bright a star really is. A star’s absolute is a characteristic of the star and does not depend on how far it is from Earth. You can calculate a star’s absolute brightness if you know its distance from Earth and its apparent brightness. Size And Mass; Once astronomers know a star’s temperature and absolute brightness, they can estimate its diameter and then calculate its volume. However, there is no direct way of finding the mass of an isolated star. Instead, astronomers are able to calculate the masses of many stars by observing the gravitational interaction of stars that occur in pairs. From such observations, astronomers have determined that, for the most stars, there is a relationship between mass and absolute brightness. Astronomers have found that many stars are similar to the sun in size and mass.Composition; A spectrograph is an instrument that spreads light from a hot glowing object, such as a light bulb or a star, into a spectrum Astronomers can use spectrographs to identify the various elements in a star’s atmosphere.
3. 3. Each star has its own spectrum. The elements within a star’s atmosphere absorb light from the star’s photosphere. Each element absorbs light of different wavelengths from the star’s continuous spectrum. The result is bright spectrum, such as absorption lines that show where light has been absorbed. Just as fingerprints can be used to identify a person, a star’s absorption lines can be used to identify different elements in the star. Absorption lines of most elements have been identified in the spectra of stars. Observations of such lines in many stars have shown that the composition of most stars is fairly similar. Most stars have chemical makeup that is similar to the sun, with hydrogen and helium together making up 96 to 99.9 percent of the stars’ mass. Questions A) 1. How can the distance to a star be measured ? 2. How do astronomers categorize stars? 3. What elements are found in stars? B) Terminology; write the meanings of the following words 1. star 2. light-year 3. parallax 4. apparent brightness 5.absolute brightness 6. absorption lines C) mass Properties stars 1. include 2.
4. 4. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ How Stars Formed The space around stars contains gas and dust. In some regions this matter is spread thinly; in others it is packed densely. A nebula is a large cloud of gas and dust spread out over a large volume of space. Some nebulas are glowing clouds lit from within by bright stars. Other nebulas are cold, dark clouds that block the light from more distant stars beyond the nebulas. Stars form in the densest regions of nebulae. Stars are created by gravity. Gravity pulls a nebula’s dust and gas into a denser cloud. As the nebula contracts, it heats up. A contracting cloud of gas and dust with enough mass to formed a star is called protostar. As a protostar contracts its internal pressure and temperature continue to rise. A star is formed when a contracting cloud of gas and dust became so dense and hot that nuclear fusion begins. Pressure from fusion supports the star against the tremendous inward pull of gravity. This new energy source stabilizes the young star, and it joins the main sequence. Adult Stars Stars spend about 90% of their lives on the main sequence. In all main-sequence stars, nuclear fusion converts hydrogen into helium at a stable rate. There is an equilibrium between the outward thermal pressure from fusion and gravity’s inward pull. A star’s mass determines the star’s place on the main sequence and how long it will stay there. The amount of gas and dust available when a star forms determines the mass of each young star. The most massive stars have large cores and therefore produce the most energy. In a large, young star with 30 times the sun’s mass, gravity exerts a huge inward force, increasing the star’s internal temperature and pressure. High-mass stars become the bluest and brightest main-sequence stars. Typically these blue stars are about 300,000 times brighter than the sun but, like gas-guzzling hot rods, large stars pay a price. Because blue stars burn so brightly, they used up their fuel relatively quickly last only a few million years Stars similar to the sun occupy the middle of the main sequence. Yellow star like the sun has a surface temperature of about 6000 k and will remain stable on the main sequence for about 10 billion years. Small nebulas produce small, cool stars that are long-lived. A star can have a mass as low as a tenth of the sun’s mass. The gravitational force in such low-mass stars is just strong enough to create a small core where nuclear fusion takes place. This lower energy production results in red stars, which are the coolest and least bright of all visible stars. A red main-sequence star, with a surface temperature of about 3500 k, may stay on the main sequence for more than 100 billion years. The Death Of Star Stars don’t last forever. When a star’s core begins two run out of hydrogen gravity gains the upper hand over pressure and the core starts to shrink. Soon, the core temperature rises enough to cause the hydrogen in a shell outside the core to begin fusion. The energy flowing outward increases, causing the outer regions of the star to expanding atmosphere moves farther from the hot core and cools to red.
5. 5. The star becomes a red giant. Eventually, the collapsing core will grow hot enough for helium fusion to occur, producing carbon, oxygen, and heavier elements. In helium fusion, the star stabilizes and its outer layers shrink and warm up. In this period, the star remains in the upper right part of the H-R Diagram. The dwindling supply of fuel in a star’s core ultimately leads to the star’s death as a white dwarf, neutron star, or black hole. The final stages for a star’s life depend on its mass. Low- And Medium-Mass Star Low mass and medium mass stars which can be as eight times as massive as the sun, eventually turn into white dwarfs. Such stars remain in the giant stage until their hydrogen and helium supplies dwindle and there are no other elements to fuse. Then the energy coming from the star’s interior decreases. With less outward pressure to support the star against gravity’s inward pull, the star collapses. The dying star is surrounded by a glowing cloud of gas. Such a cloud is called a planetary nebula because the first ones founded looked like planets when viewed through a small telescope. As the dying star bows off much of its mass, only its hot core remains. This dense core is a white dwarf. A white dwarf is about the same size as Earth but has about the same size as Earth but has about the same mass as the sun. White dwarfs don’t undergo fusion, but glow faintly from leftover from thermal energy. When a white dwarf becomes to cool to glow visible light, it is called a black dwarf. But it takes about 20 billion years for a white dwarf to cool down, so the universe hasn’t been here long enough for any black dwarfs to form yet. High-Mass Star The life cycle of high-mass star (those with a mass of more than eight times that of the sun) is very different from the life cycle of lower-mass star. As high-mass star evolve from hydrogen fusion to the fusion of other elements, they grow into brilliant supergiants. This creates new elements, the heaviest being iron. A high-mass star dies quickly because it consumes fuel very rapidly. As fusion slows in high mass star, pressure decreases. Gravity eventually overcomes the lower pressure, leading to a dramatic collapse of the star’s outer layers. This collapse produces a supernova, an explosion so violent that the dying star becomes more brilliant than an entire galaxy. Supernovas produce enough energy to create elements heavier than iron. These elements, and lighter ones such as carbon and oxygen, are ejected into space by the explosion. The heavier elements in our solar system, including the atoms in our body, came from a supernova that occurred in our galaxy billions of years ago. As a supernova spews material into space, its core continues to collapse. If the remaining core has a mass less that about three times the sun’s mass, it will become a neutron star. A neutron star is the dense remnant of a high-mass star that has exploded as a supernova. In a neutron star, electrons and protons are crushed together by a star’s enormous gravity to form neutrons. Neutron stars are much smaller and denser than white dwarfs. A spoonful of a neutron star would weigh nearly a billion tons on Earth! A neutron star with the mass of the sun would be only about 25 kilometers across, the size of a large city. Like a spinning ice skater pulling in his arms his arms, a neutron star spins more and more rapidly as it contracts. Some neutron stars spin hundreds of turns per second! Neutron stars emit steady beams of radiation in narrow cones. If the neutron star is spinning, these emissions appear to pulse on and off at regular intervals, like the spinning beacon on a light house. Each time one of these beams of radiation sweeps across Earth, astronomers can detect a pulse of radio waves. A spinning neutron start that appears to gives strong pulses of radio wave is called pulsar.
6. 6. As impressive as pulsars are, very massive star can have even more dramatic ends. If a star’s core after a supernova explosion is more than about three time the sun’s mass, its gravitational pull is very strong. Gravity causes the core to collapse beyond the neutron-star stage. As the collapse continues, the pull of gravity increases and the speed required to escape the star’s core reaches the speed of light. Beyond this point, nothing can escape and a black hole is formed. A black hole is an object whose surface gravity is so great that even electromagnetic waves, traveling at the speed of light, cannot escape from it BLACK HOLE A black hole is a region of space containing so much matter that it collapses to an infinitely dense point. The force of gravity in a black hole is so great that anything falling into it, including electromagnetic waves, becomes trapped BLACK HOLE Astronomers now think that many large galaxies, including Milky Way, have black holes in their centers. The Milky Way’s center is hidden from view by interstellar dust in the spiral arm lying between the Sun and the galaxy’s center. Radio and infrared telescopes can penetrate the dust, however. Images show a cluster of several million stars and great turbulence at the Milky Way’s core in a region about three light- years across. The high mass of These Region indicates the presence of a black hole. However, the area does not exhibit many typical black hole behaviors, such as x-ray emissions, detected in the centers of other galaxies Interpreting Diagrams An object that falls into a black hole would be crushed by its intense gravitational force.
7. 7. ANSWERS 1. Astronomers measure the parallax of nearby stars to determine their distance from Earth 2. Astronomers use several properties to classify stars. 3.Most stars have composition similar to the sun 1. A star is a large glowing ball of gas in space, which generates energy through nuclear fusion in its core. 2. A light year is the distance that travels in a vacuum in a year, which is about 9.5 trillion kilometers. 3. The apparent change in position of an object with respect to a distant background is called parallax 4. The brightness of a star as it appears from Earth is called its apparent brightness. 5. Absolute brightness is how bright a star really is. It is the characteristic of the star and does not depend on how far it is from the earth. 6. Absorption lines contain a set of dark lines that show where light has been absorbed. 7. H-R diagrams are used to estimate the sizes of stars and their distances, and to infer how stars change over time. 8. main sequence
8. 8. GALAXIES A galaxy is a huge group of individual stars, stars systems, star cluster, dust, and gas bound together by gravity. Our own galaxy is called the Milky Way. In the 1800s and early 1900s, many astronomers thought that the universe did not extend beyond the Milky Way. However observations of odd spiral- shaped objects sparked a spirited scientific debate. The debate focused on whether there so-called “spiral nebulae” were within or outside the Milky Way. The question was settled only in 1920s, after a large new telescope was built on Mount Wilson in California. Astronomers could see individual stars, proving that spiral nebulae were actually distant galaxies consisting in billions of individual stars. Astronomers now know that there are billions of galaxies in the universe. The largest galaxies consist of more than a trillion stars. Galaxies vary widely in size and shape. Astronomers classify galaxies into four main types; spiral, barred-spiral, elliptical, and irregular. The Milky Way Galaxies On a clear, dark night far from city lights, you can see a faint white band stretching across the night sky. This is the Milky Way. The Milky Way galaxy has an estimated 200 to 400 billion stars and a diameter of more than100, 000 light years. Every individual star that you can see with the unaided eye is in our galaxy. The solar system lies in the Milky Way’s disk within a spiral arm, about two thirds of the way from the center. From Earth we are looking at the rest of the Milky Way edgewise, so it appears as a band of our night sky, rather than a spiral. The Milky Way’s flattened disk shape is caused by its rotation. The sun takes about 220 million years to complete one orbit around the galaxy’s center. At the center of the galaxy is a bulge of stars surrounded by an immense halo of globular clusters. Recent evidence suggest that there is a massive black hole at our galaxy’s center. Extending outward and winding through the galaxies disk are spiral arms of gas, dust, and young stars. Stars are performing in these spiral arms. Quasars In the 1950’s astronomers were mystified by the discovery of distant objects they called quasars. By studying their spectra, astronomers have determine that quasars (KWAY zahrz) are the enormously bright centers of distant, young galaxies. Quasars produce more light than hundreds galaxies the size of the Milky Way. What makes a quasar so bright? The most likely explanation involves matter spiraling in to a supper massive black hole with the mass of a billion suns. The gravitational potential energy of this matter is transformed in to electromagnetic radiation as it falls into the black hole. THE BIG BANG THEORY If the universe is expanding , where were the galaxies in the distant past? Hubble observed that in every direction you look, galaxies at a given distance are moving away at the same rate. This is what you would expect if the universe were expanding uniformly. Astronomers theorize that the universe came in to being at a single moment, in an event called the big bang. According to this theory, all the matter and energy of the universe were at one time concentrated in a incredibly hot region smaller than the period at the end of this sentence. The big bang theory states that the universe began in an instant, billions of years ago, in an enormous explosion. After The Big Bang The universe expanded quickly and cooled down after the big bang. After a few hundred thousand years of expansion, the universe was still much smaller and hotter than its now, but cool enough for atoms to form. Gravity pulled atoms together into gas clouds that eventually evolved
9. 9. into stars in young galaxies. The sun and solar system is formed about 4.6 billion years ago when the universe was about two thirds of its present size. Evidence for the theory In 1965, two American physicist, Arno Penzias and Robert Wilson, noticed a signal on their radio telescope that they couldn’t explain. They eventually realized that they were detecting a faint distant glow in every direction. Today this glow is called the cosmic microwave background radiation. This glow is energy produced during the big bang, still travelling throughout the universe. The existence of cosmic microwave background radiation and the red shift in the spectra of distant galaxies strongly support the big bang theory. The big bang theory describes how the expansion and cooling of the universe over time could have led to the present universe of stars and galaxies. It offers the best current scientific explanation of the expansion of the observable universe. Variations of the theory continue to be proposed and are being tested with new observations. Age Of The Universe Since astronomers know how fast the universe is the is expanding now, they can infer how long it has been expanding. If you travelled backward in time, all of the matter in the universe would be at its starting point 13 to 14 billion years ago. Recent measurements of the microwave background radiation have led to a more precise age. Astronomers now estimate that the universe is 13.7 billion years old. Asteroids They are minor planets or remains of a planet found in the solar systemThe asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets.
10. 10. Spiral Galaxy Barred spiral galaxy
11. 11. Elliptical galaxy, Irregular galaxy
12. 12. Milky Way The Milky Way, or simply the Galaxy, is the galaxy in which the Solar System is located. It is a barred spiral galaxy that is part of the Local Group of galaxies. It is one of billions of galaxies in the observable universe. ‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘ SPM PRACTICES Objective questions; In 1929, Edwin Hubble introduced the Big Bang theory. Stars and planets are too far away that if we are to measure the distance in kilometers, the number would be enormous. Instead scientists measure such distances in light years. Light travels at 300,000 km per second so a light year is the distance light travels in one year- 9,460,000,000,000 km. 1. Distance in space are measured in A) seconds B) kilometres C) light years D) million years Most heavenly bodies, such as comets and asteroids, are too distant to be reached by human beings. Hence , most missions have incorporated the use of space probes. Some space probes are only able to orbit around the planet in order to make observations and take photographs, such as the space probe Magellan. Others, such as the Galileo, can
13. 13. examine the atmosphere of a planet before landing on the surface. Some space probes can land and send back information on the chances of life on a planet. 2. Why do space missions incorporate the use of many space probes? A) To study the chances of life on a planet B) To examine the atmosphere of the planet C) To make observations by orbiting around planets D) To obtain a wide range of information about a distant planet A. What are the followings?  Comets …………………………………………………………………………………………………………………………………… …..  Meteoroids………………………………………………………………………………………………………………… ……………….. B. Writing; Should the moon be developed? Giving viewpoints, Develop the moon Do not develop the moon *many advantages *waste of time and money *to gain scientific knowledge-early history of *government funds better spend on more solar system immediate effect projects eg svhools, feeding the hungry *tourist destination *development of the moon would be too *cost would be high but many people will be costly and risky willing to pay for the unique chance to experience the moon’s low gravity, airless *techniques of mining on the moon is environment uncertain. *rich in minerals-iron, aluminum and *such resources would be too expensive to calcium. produce *they could be mined for Earth *stepping stone for future mission to Mars *technology can improve people’s lives and create new job.
14. 14. Answers: B.Comets: chunks of rock and ice. Meteoroids consist of rock or metal and they can be any size from tiny particles to huge boulders. When in space they are meteoroids, as they enter the Earth’s atmosphere, they are meteors and when strike the Earth’s surface they are meteorites. Sample answer; C.Develop the moon; Developing the moon will have many advantages. One is to gain scientific knowledge, especially about the early history of solar system. The moon will be the ultimate tourist destination. Although the cost would be high, many people would be willing to pay for the unique chance to experience the moon’s low gravity and airless environment. The moon is rich in a variety of minerals, including iron, aluminum and calcium. Once permanent lunar base is established, these resources could be mined for use on Earth or for the eventual colonization of space. The moon is a logical stepping stone for future missions to Mars. A lunar vase would provide a valuable testing ground for technology that would eventually be useful on Mars. Such technology will also have applications on earth, where it will improve people’s lives and create new jobs. Do not develop the moon; The development of the moon would be a waste of time and money. Scarce government funds would be better spent on projects with a more immediate benefit, such as feeding the hungry, improving schools, and building better housing. In the short run, government funding for space should be focused on space probes and telescopes. A mission sending crew to Mars would be of much greater interest and scientific value. The proposed development of the moon would be too expensive and risky to receive private funding. Few tourists are likely to be able to pay the high costs of visiting a resort on the moon .The techniques for mining minerals and energy resources on the moon are uncertain, and any such resources would probably be very costly to produce.