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AS 101 Module 2.docx

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Department
Astronomy
Course
AS101
Professor
Arthur Read
Semester
Winter

Description
AS 101 Module 2  Old But Good Astronomy o Planets so important that the days of the weeks are named after the 7 visible objects that have been seen for centuries  Sun—Sunday  Moon—Monday  Mars—Tuesday  Mercury—Wednesday  Jupiter—Thursday  Venus—Friday  Saturn—Saturday o Stonehenge  South of England, 1200 to build, 4000 years old, 2000B.C  Construction attributed to the Druids –John Aubrey  Romans said Celtic priesthood, but was already built by then  Late 3000BC Neolithic period, new economy arising  Beaker Folk—pottery drinking vessels used, began to use metal, possibly immigrants  Connections to astronomy  Observers standing at the centre see the sun rise directly over Heel stone on the Summer Solstice (June 21) o Templo Mayor  Near Mexico city, Aztec and Mayans o Kukulcan’s Pyramid- Chichen Itza  Square based, stepped pyramid, 75 feet tall  During vernal equinox (March 21) and autumnal equinox (September 21) at 3pm sunlight bathes the Western balustrade of pyramid’s main stairway  Causes seven isosceles triangles to form imitating the body of a serpent 37 yards long that creeps downwards until it joins another serpent’s head carved in stone at the bottom of the stairway o Big Horn Medicine Wheel (Wyoming, USA)  Rocks strategically placed on the ground in the form of a giant wheel with spokes aligned with the rising and setting of the Sun, Moon and bright stars o Caracol temple in Mexico at Chchen Itza  Windows are aligned with atronomical events, esp Venus (Mayans) o Lunar Cycles  29.5 day lunar cycle used by most ancient civilizations  19 calendar years is almost exactly 135 lunar months= same lunar phases on about the same dates every 19 years  Metonic cycle—Mike Meton 432 BC, cycling of the moon  Easter date varies annually because it is related to lunar cycles  Easter Sunday is always the Sunday following the first full moon after the Spring equinox  Saros cycle—cycle of eciplses  From Greeks to Galileo and Newton o The Greek Influence  Thales  Universe is rational and understandable, mysteries of the world are because they are unknown  Pythagoras  Relationships in nature developed with geometric and math relationship  Planets produce music as they orbit – music of the spheres  Socrates  Virtue is understand and that no human knowingly does wrong  Questioning people on positions they asserted and working them through questions into a contradiction, thus proving to them that their assertion was wrong  Plato  Theory of ideas- love is a desire for union with beaty, ascending scale of perfection from passion to ectasy in comtemplation of designating love for a person, that is free of carnal desire—Platonic love  Artistotle  World could be understood fundamentally through the detailed observation and catlogueing of phenomena – empirical (science)  Universe is two parts; Earth (centre of universe) and the heavens  Inductive reasoning—learning what was known about topic, gain consensus, test, and work out underlying principles – scientific method  Ptolemy  Predicted planetary events in the future  Retrograde motion of planets issue of , put planets on epicycles  Used earth centred universe  Copernicus  Claimed sun-centred solar system  Held that orbits had to be circular  Brahe  Greatest naked-eye observer of all time  Expected conjunction of Jupiter and Saturn late by two days  Kepler  Birth of modern science  First Law—orbit of plants around suns an ellipse with the sun at one focus o Ellipse—two foci( one is the sun)  Major axis- line drawn between foci  Semi-major axis is half  Minor axis- perpendicular to the major axis  Eccentricity—ratio of the distance between the two foci to major axis. Circle= 0 straight=1  Second Law o As a planet orbits, sweeps out equal areas in equal time o When the planet is closer to sun move faster along order than when close to aphelion  Third Law o Squares of the periods of any two planets have same ration as cubes of their semi- major axes o p = a3 o p= orbital period in Y , a= average distance from Sun AU  matched Brahe’s model best  Galileo Galilei  Invented the telescope used first in 1609  Observerd more stars in Milky Way than could be counted, four moons Jupiter, phases of Venus  Irregular surface of the moon  Viewing of Jupiter and its point of light turned out to be its moons o Earth-centered solar system; Venus revolves around sun o Isaac Newton  Force- a push or a pull  Gravity—invisible force existing between two objects  Universal of Gravitation  Gravitational force is proporational to the masses of both object and inversely proportional to the square of the distance between the masses  If the mass of either object is boubles then the force also doubles  Kepler’s law  Applied to any two bodies moving under the influence of gravity, orbit with centre mass at one focus  Elliptical orbits are bound or closed orbit, circle each other forever rd  Parabolic and hyperbolic orbits—unbound or open orbits  3 Law  P2=4π2a3G /(M1+M2) P2=(4π2GMs)a3  Determine mass by measuring orbital rate (P) and average distance from Sun (a)  Tides  The side of Earth facing Moon feels stronger gravitational attraction  As earth rotates inside its bulge, moves through each once per day o Two high tides and two low tides o Do not occur at same time everyday  Sun—noticeable when S, M, E lined up and full or new M o Tides are highest time of month= spring tides o 1 and 3 quarter M = neap tides; sun cancel out lunar tides  Tidal friction o Rotation of Earth gradually slowing down, moon further away o Moon’s synchronous rotation around earth  The Scientific Method o Deductive and Inductive Reasoning  Deductive reasoning—process of concluding that something must be true because it is a special case of a general principle that is known to be true  Logically valid, show how mathematical facts are true  Inductive Reasoning—process of reasoning that a general principle is true because the special cases you’ve seen to be tue  Constructing a general principle from special cases o Scientific Method  Looks at a set of observations, develops a hypothesis satisfying the observations, further observation, testing hypothesis and making adjustments  Observations—set of observed facts  Hypothesis—model to explain the observations and make new prediction
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