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339349682-Origin-of-Modern-Astronomy.ppt - Ancient...

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Ancient AstronomyModern astronomy traces its roots to Mediterraneanorigins (Iraq, Greece, and Egypt)Ancient observers were aware of many phenomenathat could be observed with the naked eyeAccurate measurement of the length of the year (3000 B.C.)Correct explanation of eclipses (500 B.C.)Cycles of lunar and planetary motionsGreeks and Chaldeans were aware of the 18–year pattern ofeclipses (saros cycle)more than 2000 years agoPrecession (subtle shifting of star positions over the years)was discovered by Hipparchus (150 B.C.)The early Greeks were the first to tie known laws ofnature to an understanding of the universe (cosmology)Modern science is descended most directly from the Greeks
Babylonian AstronomyThe Babylonian civilization flourished for manycenturies, beginning around 2000 B.C.Modern-day IraqBabylonian astronomers knew the length of the yearto an accuracy within a few minutes of the modernvalueDone by noting that length of shadow of fixed stake changesduring the year (Sun’s altitude above horizon varies)Length of year = time it takes for shadow to progressthrough full cycle of varying lengthsBabylonians developed a 360-day calendar havingtwelve 30-day monthsOccasionally a 13thmonth was added (“leap month”)
Babylonian AstronomyFull circle of sky was divided into 360 parts,corresponding to Sun’s position each day of the yearBabylonians originated modern system of angularmeasure (360° in a full circle)Babylonians thought number “60” was special (dividesevenly into 360, and is evenly divisible by 12)Thus each degree has 60 parts (arcminutes) and each arcminutehas 60 parts (arcseconds)Babylonian timekeeping system worked in the same wayBabylonians developed mathematical descriptions ofplanetary motionsWere able to determine the synodic period (time neededfor planet to complete full cycle of orbital configurations) ofsome planetsNever developed physical model of solar system
Babylonian AstronomyBabylonian studies were motivated by astrology(pseudo-science involving belief that positions ofcelestial objects influence events on Earth)Driven by relationship between Sun’s motion andseasonal eventsNo scientific basis exists for astrologyAssyrian and Chaldean cultures maintainedBabylonian records and teachings, and added tothemChaldeans developed tables predicting motions of Sunand Moon and when eclipses occurGradually center of knowledge and influence shiftedto the west toward shores of Mediterranean
Early Greek AstronomyGreek astronomical centers:Earliest Greek civilization arose on island of Crete(5000 to 2000 B.C.)Mythology of the constellations is attributed to earlyMinoan culture on Crete
Early Greek AstronomyGroupings of stars probably named inhonorof thecharacters in Greek mythology, rather than due toan actual resemblance of people or objects
Early Greek AstronomyThe beginnings of formal scientific thought aretraced to Greek philosopher Thales(circa 624–547

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Planet, Kepler s laws of planetary motion, Heliocentrism, Babylonian astronomy, History of astronomy, On the Heavens, Physics,

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