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Changing Views of the Solar SystemListen as each group presents information about their assigned scientist. Record the information you learn in the table below:ScientistWhen?Discovery or TheoryAs you read your article, answer the following questions:When did this Astronomer live?What contributions did this Astronomer make to our understanding of the Universe?Do we still believe this Astronomer’s theories? (Explain why or why not)Did this Astronomer build on the works of others? Was there someone who inspired this Astronomer?Summarize this Astronomer’s theory in 2-3 sentences:4326255-396875 Aristotle428 BC to about 384 BCAristotle was born in Stagira, Greece, in 384 BC. He was sent to be a student at Plato's Academy, and eventually becomes a teacher himself there. He was the tutor of Alexander the Great. When Plato died, and Aristotle was not chosen to take over Plato's Academy, he formed his own school in Athens called the Lyceum. Aristotle wrote about almost everything, including astronomy.Importance to AstronomyThese men knew that we see the moon by the light of the sun, how the phases of the moon occur and how eclipses work. (The Greeks had known this for a while.)Aristotle knew that the earth was a sphere. He argued that each part of the earth is trying to be pulled to the center of the earth, and so the earth would naturally take on a spherical shape. (Gravitationally, this is actually accurate!) He noticed the shadow of the earth on the moon during a lunar eclipse was always circular. The only shape that always casts a circular shadow is a sphere. Second, as one traveled more north or south, the positions of the stars in the sky change. There are constellations visible in the north that one cannot see in the south and vice versa. (He used this to also argue that the earth isn't very big, because you don't have to travel very far to notice the difference.) Aristotle believed in an earth centered model of the planets. In these models, the center of the earth is the center of all the other motions. We refer to this idea as “Geocentrism” (geo = earth). (Metaphysics, Book XII, Part 8)Aristotle rejected a moving earth for two reasons. Most important is that he didn’t understand inertia. To Aristotle, the natural state for an object is to be at rest. He believes that it takes a force in order for an object to move. Using Aristotle's ideas, if the earth were moving through space, if you tripped, you would not be in contact with the earth, and so would get left behind in space. Since this obviously does not happen, the earth must not move. This misunderstanding of inertia confused people until the time of Galileo.Aristotle believed that the objects in the heavens were perfect and unchanging. Since he believed that the only eternal motion is circular with a constant speed, the motions of the planets must be circular. Aristotle and his ideas became very important because they were incorporated into the Catholic Church's theology in the twelfth century.3820160-55245Claudius Ptolemy85 AD to 165 ADShort BiographyVery little is known of Ptolemy's life. He most likely grew up in or near Alexandria, where he studied mathematics and astronomy. While he is most known for his work in mathematical astronomy, he wrote a number of other books that have survived, including Optics and Geography, which was an attempt to make a map of the world as known by Ptolemy with latitude and longitude measurements.Importance to AstronomyPtolemy wrote the Almagest around 150 AD. With the Almagest, Ptolemy produced the first working, predictive model of the solar system in the world, and was the culmination of Greek astronomy and the geocentric model. The Almagest was a complete textbook in mathematical astronomy, and was so successful that it became the standard in mathematical astronomy for 1400 years. 32124651177925The Almagest itself was broken into 13 chapters. He begins by teaching all the mathematics that is needed for the computations in the book, and then goes on to give detailed descriptions of how to make astronomical observations and mathematical models for the sun, moon and planets. He includes mathematical tables and star charts, and explains how to improve on observational data. The Greek geocentric model is still often called the Ptolemeic system in honor of this achievement.In the Ptolemaic model, one only needs a few key pieces of information to predict where a planet is at any point in time. Ptolemy not only gives all this information to the reader of his book, he explains how to make one's own observations and calculate what each parameter is. Given only 7 parameters, one can then calculate where a planet is at any point in time. It is important to note that this model worked reasonably well. In fact, it worked so well, that it was the standard model for almost 1400 years. The diagram to the right shows the order of the planets in the Ptolemeic system. Note that if one switches the earth and the sun, then this matches the correct order of the planets. Ptolemy simply based this on the rates of the rotations.4092575-247015Nicholas CopernicusFebruary 19, 1473 to May 24, 1543Born in Torun, PolandImportance to AstronomyCopernicus believed in the Principal of Uniform Circular Motion - possibly even more so than Ptolemy. He ends up proposing a heliocentric theory, the theory that the Sun is in the center of the Universe. Around 1511, he circulates a little manuscript called Commentariolus in which he lays out a general framework for a model of the solar system, which he bases on the following seven ideas:There is no one center of the orbits of the all the planets.Only the moon goes around the earth.All the planets, including the earth, go around the sun.The stars are immeasurably far away.The stars don't move - they only appear to move because the earth rotates once a day on its axis.The sun doesn't move - it only appears to move because the earth revolves around the sun.He doesn't offer any real details of the theory, just lays out what things would look like. He promises a fuller version in the future, and he works on his theory for the next 30 years.There are some important points regarding these postulates. He said that the stars are really far away to account for the fact that there was no visible stellar movement. Also, the sun does not have any role in the mechanics of the solar system; it is simply hanging out near the various centers of the orbits of the planets. In fact, Copernicus does not concern himself with any causes of the motions, all he is trying to do is mathematically model them.In 1543, the full treatment of the heliocentric theory, De Revolutionibus Orbium Coelestium, is finally published. Copernicus probably only saw the first copies on his deathbed. The book itself is a masterpiece - and mirrors Ptolemy's work in scope and ordering. (Since he was working by himself in his spare time it is no wonder it took him 30 years to produce.) Ptolemy's work was so successful and so well-accepted,perhaps Copernicus knew that he needed to produce a model as detailed and all-inclusive as Ptolemy's. This is the first competitor to Ptolemy's theory in over 1400 years. So why did some people really dislike the Copernican model? In short, they could not get over the fact that we don't sense that the earth is in fact rotating on its axis and going around the sun. Science had still not figured out what inertia was, and people honestly thought that if the earth were rushing through space trying to go around the sun, then every time you jumped up in the air, you would get left behind by the fast moving earth. Because of this, a lot of people could not accept a planetary model that involved a moving earth.-13970190500Galileo GalileiFebruary 15, 1564 to January 8, 1642Born in Pisa, ItalyIn 1609, Galileo heard of early telescopes, built his own, and looks up at the night sky with his (at the time) high quality telescope. He was astounded by what he saw.By the winter of 1610, Galileo had observed Venus over a few months, and watched how Venus was undergoing phases, like the moon. This was a major discovery, as it proved that Venus had to go around the sun, thus disproving the Ptolemeic theory.Through 1611-12, Galileo made observations of sun spots, along with a few other scientists at the time. He made very accurate drawings of what he saw, and was able to show that the sun was spherical and rotated from his observations.The number of discoveries made with the telescope ignites a battle between the geocentrists and the heliocentrists. Galileo also wrote a number of letters to important people regarding the Bible and scientific knowledge. (Some of these became quite widely circulated.) In these letters, Galileo argues that the point of the Bible was not to teach scientific principles, and that it often speaks figuratively in order to be more easily understood. In the "Letter to the Grand Duchess Christina" Galileo quotes someone "That the intention of the Holy Ghost is to teach us how one goes to heaven, not how heaven goes."In 1616 Cardinal Bellarmine, the Catholic Churches lead theologian called Galileo into Rome for a meeting. Galileo was told that Copernicus' book was going to be put on the list of Prohibited Books and that he should not teach that the earth goes around the sun. Basically, without any real proof that the earth went around the sun and rotated on its axis, the Catholic Church would not budge on the matter of Biblical interpretations.Galileo is ultimately found guilty of teaching the Copernican system and not teachings from the Bible. Galileo was put under house arrest for the rest of his life, and also prohibited from writing any more books. (Galileo does write one more book anyways - the follow up to the ideas of motion that he talked about in the the Dialogue, but it has to be smuggled out of Italy in order to be published.)Galileo never found his proof that the earth moved. But between his work straightening out the physics of motion, his (and others) numerous telescopic observations the geocentric model of the Solar System no longer made any sense.4270375-410210Johannes KeplerDecember 27, 1571 to November 15, 1630Born in Weil der Stadt, GermanyImportance to AstronomyFrom his days as a student, Kepler believed in the model of the Universe described by Copernicus. Kepler proposed that the planets are all moving around the sun due to a force somehow exerted by the sun on the planets, and that this force weakened the farther from the sun a planet was. Kepler was a math teacher, but he also did some important work in the field of optics. He invented an improved version of the refracting telescope. He used these new telescopes to better analyze solar and lunar eclipses. Kepler noticed that the shadows cast during the eclipses were unexpected. In 1604 a very bright “new” star was shining in the sky. Kepler did not believe that this object was a star. He noted that the object’s luminosity (brightness) was fading and he eventually determined that the object was a Super Nova.3 Laws of Planetary MotionBy 1618, Kepler had discovered what are now called Kepler's 3 laws of Planetary Motion. The two laws you should know about are listed here:Planets orbit the sun in an ellipse, or oval shape. There are distinct points of the oval shape: perihelion (closest distance to the sun), aphelion (farthest distance to the sun). Kepler pointed out that the orbits were ALMOST perfectly circular, and that the slight oval shape wouldn’t normal be noticed without using a LOT of math.As a planet goes around the sun, it speeds up as it gets closer to the sun and slows down as it gets farther away from the sun.380619060325Kepler also used math and geometry to predict that there are only 6 planets in our Solar System, no more and no less. He did this by fitting geometric shapes around the orbits of planets to predict where the next planet should be. The picture to the right shows a diagram of Kepler’s model of our Solar System. Each geometrical shape (pyramid, cube, etc.) indicates the orbit of a planet in our Solar System.4284345-137160Sir Isaac NewtonJanuary 4, 1643 to March 31, 1727Born in Woolsthorpe, Lincolnshire, EnglandSir Isaac Newton was an English physicist and mathematician who is widely regarded as one of the most influential scientists of all time and as a key figure in the scientific revolution. Newton's Principia formulated the laws of motion and universal gravitation that scientists used for the next 300 years. Newton’s Three Laws of Motion (simplified)An object that is at rest will stay at rest until it is acted upon by an outside force. And an object in motion with stay in motion until it is acted upon by an outside force.The force of an object is equal to the object’s mass multiplied by the object’s acceleration. (Faster and heavier = more force)For every action there is an equal and opposite reactionNewton also demonstrated that the motion of objects on the Earth and that of celestial bodies shared the same principles. This means that objects here on earth are acted upon by gravity, and that objects in outer space are also acted upon by the same force. Newton improved Kepler’s laws of Planetary Motion, finally proving the heliocentric model of the solar system. (Heliocentric means that the sun is in the center of the solar system).Newton built the first practical reflecting telescope (with a model shown below). Newton was also one of the first scientists to develop a prism that could separate colors into the rainbow pattern. This discovery would later help future astronomers to develop spectroscopes!148717051435 Edwin Hubble4231640-146050November 20, 1889 – September 28, 1953Born in Marshfield, Missouri Hubble was an American astronomer who is generally regarded as one of the most important observational astronomers of the 20th century. Hubble is known for showing that the speed of a galaxy increases with its distance from the earth, implying the universe is expanding. Edwin Hubble also provided evidence that many objects that were classified as "nebulae" were actually galaxies beyond the Milky Way. Edwin Hubble supported the Doppler shift interpretation of the observed redshift in galaxies.Importance to AstronomyThe universe goes beyond the Milky Way galaxyIn 1919 the prevailing view was that the universe consisted entirely of the Milky Way Galaxy. Using the Hooker Telescope, Hubble identified Cepheid variables (a kind of star) in several spiral nebulae, including the Andromeda Nebula and Triangulum. His observations, made in 1922–1923, proved that these nebulae were much too distant to be part of the Milky Way and were, in fact, entire galaxies outside our own. This idea had been opposed by many in the astronomy establishment of the time. Despite the opposition, Hubble, then a thirty-five-year-old scientist, had his findings first published in The New York Times and American Astronomical Society. Although some of his more renowned colleagues simply scoffed at Hubble's idea of an expanding universe, Hubble ended up publishing his findings on nebulas. This published work earned him an award titled the American Association Prize and five hundred dollars.Hubble also devised the most commonly used system for classifying galaxies, grouping them according to their appearance in photographic images. He arranged the different groups of galaxies in what became known as the Hubble sequence.Redshift increases with distance Hubble discovered a connection between objects' distances with their red shifts. In 1929 Hubble formulated the Redshift Distance Law, nowadays termed simply Hubble's law. Although concepts underlying an expanding universe were well understood earlier, this statement led to wider-scale acceptance for this view. The law states that the greater the distance between any two galaxies, the faster they move away from each other. This discovery was the first observable support for the Big Bang theory, showing that the universe is expanding. ................
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