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A History of Astronomy

A History of Astronomy. Any theory of the Universe has to explain the following:. Motion of stars, Sun, and Moon Phases of Moon Retrograde motion of planets (the “wanderers”) Varying brightness of planets (and some stars). A Timeline of Astronomers. Ancient Astronomy Aristotle (~350 BC)

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A History of Astronomy

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  1. A History of Astronomy

  2. Any theory of the Universe has to explain the following: • Motion of stars, Sun, and Moon • Phases of Moon • Retrograde motion of planets (the “wanderers”) • Varying brightness of planets (and some stars)

  3. A Timeline of Astronomers Ancient Astronomy • Aristotle (~350 BC) • Ptolemy (~140 AD) Middle Ages Astronomy 3. Copernicus (1473-1543) 4. Tycho Brahe (1546-1601) 5. Johannes Kepler (1571-1630) Modern Astronomy 6. Galileo (1564 – 1642) 7. Isaac Newton (1642 – 1727)

  4. Part 1: The Ancient Astronomers

  5. 1. Aristotle(~359 BC, Greece) • Proposed Geocentric theory of universe: • Earth is at the center of everything • Everything else revolves around Earth • Very popular and influential idea • Universe made of 55 concentric spheres • But still couldn’t explain retrograde motion of planets

  6. Aristotle’s Universe

  7. 2. Ptolemy(~140 AD) • More detailed version of Aristotle’s geocentric model • Planets moved on small spheres called epicycles that revolved around the larger celestial sphere • What it kinda looks like

  8. Other Players • Pythagoras (~520 BC) • Aristarchos (~280 BC) • Eratosthenes (~230 BC) • Arabs

  9. Part 2: The Middle Age Astronomers

  10. Copernicus(1473-1543, Poland) • 1st to go “mainstream” with “heliocentric” model of universe • Published in Des Revolutionibus in 1543 (on his deathbed)

  11. The Heliocentric Model • Sun at center of universe • Planets orbit sun in perfect circles • Stars on a huge fixed sphere (the firmament)

  12. Advantages of Copernicus’ Model • Explained retrograde motion using passing orbits • Correctly ordered planets • Correctly calculated time for planets to orbit sun • Explained apparent motion of stars and sun using Earth’s rotation and orbit • Explained why Mercury and Venus are always seen near the Sun

  13. Problems with Copernicus’ Model • Still used some epicycles to “tweak” results to fit observations • Odd ideas about orbits?

  14. Tycho Brahe(1546-1601, Denmark) • One of the best observers in the history of astronomy • Lost his nose… • Court Astronomer of Denmark • Home/castle/observatory of Uraniborg • Not a nice guy to work for

  15. More Tycho • Court astronomer of Emperor Rudolf in Prague • Mentor of Johannes Kepler…. • 1601 – Dies of ruptured bladder. Ouch.

  16. Tycho’s Contributions • Established that the “sphere” of the firmament changes (supernova, etc.) • Left a huge catalog of detailed observations and measurements

  17. Johannes Kepler(1571-1630, Germany) • Influence of family • More of a mathematician and theorist than astronomer • Student of Tycho, inherited his observations and instruments at age 30 • “Imperial Mathematician” in Prague

  18. Kepler’s 3 Laws of Planetary Motion (1609) 1. The orbit of a planet is an ellipse, with the sun at one focus. (A Bit Exaggerated)

  19. Kepler’s 2nd Law of Planetary Motion 2. When a planet is nearer the sun in its orbit (perihelion), it moves faster. When it’s farther from the sun (aphelion), it moves slower.

  20. Kepler’s 3rd Law of Planetary Motion 3. The larger the planet’s orbit, the longer it takes.

  21. Other, Not-as-Successful Pursuits, Part 1: Astrology “Astrology is the silly daughter of the noble lady Astronomy, but with the salaries of mathematicians being what they are, the mother could not live if the daughter did not earn money.”

  22. Other, Not-as-Successful Pursuits, Part 2: Orbits as Geometric Solids

  23. Part 3: The Modern Astronomers

  24. Galileo Galilee(1564–1642, Italy) • First modern experimenter, including ball drop from Tower of Pisa • 1st to publish in Italian…Not Latin! • Many astronomical accomplishments…

  25. Galileo’s Astronomical Accomplishments • 1st to use new-fangled “telescope” to look at sky (only 14X magnification) • Saw stars visible only with telescope, not with naked eye (500 in Orion alone!)

  26. More Galileo • Discovered mountains, craters, and plains on Moon • Discovered phases of Venus

  27. And More Galileo • Discovered sunspots on Sun

  28. Still More Galileo • Discovered 4 moons orbiting Jupiter

  29. Progress at Personal Cost • Placed under house arrest by Catholic Church and made to confess “vainglorious ambition” and mistakes of “pure ignorance” (aka – renounce Copernicanism) • Not all religious: some political and personal rivalries, too • Worked on laws of motion and falling bodies until his death (8 years later)

  30. Isaac Newton(1642-1727, England) • Not expected to live over a few hours…instead lived 84 years and 3 months • Served as England’s “Master of the Mint” • Knighted in 1705 • MANY contributions…

  31. Newton’s Contributions • Invented calculus (at age 23!) • Realized that “white light” can be broken down into colors of rainbow using a prism (age 30) • Invented reflecting (mirror-based) telescope, a great improvement over Galileo’s refracting (lens-based) telescope

  32. More Newton • 3 Laws of Motion. Nuff said. • Derived Kepler’s 3 Laws. • Law of Gravity: • Gravity exists between any 2 objects that have mass • Gravity is always attractive, never repulsive • Gravity increases with increasing mass • Gravity decreases with increasing distance

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