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Historical Astronomy

Historical Astronomy. Aristotle to Kepler. Ancient Astronomers. Egyptians Babylonians Native Americans Chinese Celts Many Others. Early Observers. Big Horn Medicine Wheel. Stonehenge. Loanhead of Daviot. Pyramids of Giza. Greek Astronomers.

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Historical Astronomy

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  1. Historical Astronomy Aristotle to Kepler

  2. Ancient Astronomers Egyptians Babylonians Native Americans Chinese Celts Many Others

  3. Early Observers Big Horn Medicine Wheel Stonehenge Loanhead of Daviot Pyramids of Giza

  4. Greek Astronomers Tried to explain the motion of celestial objects Built Cosmological Models to explain observations Stars, Moon, Sun easily explained Planets (wanderers) not so easily explained

  5. Scientific Method Use models to explain observations Test models Theories are never “true” just “not false”

  6. Chain of Scientific Method Observation Explanation Prediction

  7. Early Greek Astronomers Eratosthenes calculated circumference of the earth within 5% accuracy Aristarchus proposed a heliocentric cosmos and easily explained the motion of the Sun through the heavens His writings were lost at Alexandria along with Hypatia

  8. Aristotle 384-322 B.C. Member of Plato’s Academy Philosopher and Scientist One of the 1st Physical Models of the Cosmos Geocentric

  9. Ptolemy Geocentric Attempted to explain retrograde motion Used Hipparchus idea of epicycles and deferents Added the equant Very complicated Inconsistent rules

  10. Ptolemy’s Solution Planet Epicycle Earth Equant Deferent

  11. Triumph and Tragedy Geocentric Model persisted for many, many, many, many years Lack of observable Stellar Parallax Painter’s Thumb-Parallax Parallax-Greek 'alteration' Stars are too far away!

  12. Copernican Revolution 1473-1543 A.D. Revived early heliocentric models Retrograde motion simply explained Circular Orbits No public support

  13. Copernican Retrograde http://csep10.phys.utk.edu/astr161/lect/index.html

  14. Copernicus says… The celestial spheres do not have just one common center The Center of Earth is not the center of the universe but instead only the center of gravity and of the lunar orbit All spheres revolve around the Sun

  15. He continues…. The firmament is far away Apparent motions of the firmament and Sun are actually due to Earth’s motions The apparent retrograde and forward motion of the planets is actually due to the Motion of the Earth

  16. Finally Somebody Gets It! Johannes Kepler 1571-1630 Worked for Tycho Brahe, inherited his data Heliocentric model (29 years!)‏ Found orbit shapes by observation from different points in Earth’s orbit

  17. "By the study of the orbit of Mars,we must either arrive at the secrets of astronomyor forever remain in ignorance of them."Johannes Kepler

  18. Kepler’s 1st Law Elliptical Orbits not Circular!

  19. Ellipse Geometry

  20. Kepler’s 2nd Law Equal Areas in Equal Times Describes Single Planet is orbit around the Sun Perihelion-closest approach to Sun Aphelion-farthest distance from Sun

  21. Kepler’s 3rd Law The more distant a planet’s orbit is from the Sun, the slower it moves Compares planets to one another Period- time for one complete orbit around sun Let’s see all three in action

  22. Kepler’s Triumph Published first two laws in 1609 Calculations only for Mars Decade later he checks all known planets They work! Also introduces 3rd law at this time

  23. Summary Models are constantly being evaluated Theory is never “true” just not “false” Example geocentric cosmos Kepler’s 3 laws accurately and simply describe the motion of the planets Laid the foundation for work of future scientists http://www.occc.edu/dburris/astrolecs/Historical%20Astronomy.ppt

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