Historical Astronomy 10000BC-3000BC

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Historical Astronomy 10000BC-3000BC

•   10000BC
• constellations, lunar cycle,  discovery of
  planets?
• calendar refinements for agriculture
• counting schemes
• months, year (in months, but uneven)
• 3000BC
• of days in year 360
• (360 degrees in circle)
• heliacal rise of Sirius in Egypt -gt 365 days
• celestial pole
• modern constellations (from Med. sailors)
• solstices, equinoxes, Astrology
• astronomical monuments (Stonehenge, Pyramids,
  etc.)
• astronomy strong in Mesopotamia/Europe, China,
  Africa, Polynesia, Americas everywhere!

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Ancient Astronomy around the World
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Greek Astronomy 500BC-350BC

• 500BC
• Pythagorus - concentric celestial spheres for
  Sun, Moon, planets - all bodies spherical
  (including Earth)
• Philolaus - Earth goes around central fire (Sun)
• 350BC
• Aristotle - Sun is further than Moon (slower
  against stars), eclipses - Earth is round (shadow
  on Moon), going north makes pole star rise
• choose geocentric model
• feels like it no stellar parallax

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Greek Astronomy - Geometry

• 300BC
• Aristarchus - size of Sun and Moon relative to
  Earth, relative distances (use of geometry to
  deduce them)
• using geometrical reasoning D(sun)/D(moon)20  , 
  R(earth)/R(moon)20  ,  R(sun)/R(earth)7
• Sun is much bigger, so choose heliocentric model 
  (doesn't take hold, Aristotle wins)

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The Size of the Earth

• Eratosthenes determines the true size of the
  Earth
• (and gets it right)
• using the day when the Sun
• shines right down a well at
• the solstice

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Greek Astronomy Modern Foundations

• 150BC
• Hipparcos - star catalog (850, position and
  brightness)
• - better estimates of size and distance of Moon
•   R(earth)/R(moon)8/3, D(moon)60R(earth),
  D(sun) big
• - precession of Earth's pole
• -epicycles and deferent (used by Ptolmey) to
  explain retrograde motion of planets
• 150AD
• Ptolmey - worked out a full geometric geocentric
  cosmology
• - accounts for retrograde motion of planets
• - predicts planetary positions
• - 55 concentric cosmic spheres, all circular
  motion
• (size of Universe about 20000R(earth))

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Ptolemys Model
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The Copernican System
Nicolas Copernicus 1473-1543 Poland
Ptolemaic system was looking shaky because better
observations (Arab) showed it kept missing the
planetary positions.
Copernicus recognized that a heliocentric
explanation was much simpler (but he just thought
of it as asthetically better). It didnt actually
predict the positions better.
The Church was invested in the Ptolemaic system
(tradition), and Copernicus waited until his
death to publish. Most didnt believe him.
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Galileo (1564-1642)

• Professor, engineer, scientist, writer, heretic
• One of the first to use experiment to deduce
  physical laws
• Laws of motion, velocity, acceleration, inertia,
  pendulums, falling bodies
• Brought telescopes to Astronomy
• After initial skepticism, adopted Copernican
  model because of empirical evidence in support

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Galileos discoveries
Celestial bodies are not perfect mountains on
Moon, sunspots The Earth is not the only
center of rotation (moons of Jupiter) Venus
goes in front of and behind the Sun (cant happen
if Ptolemaic system is right)