PowerPoint Presentation Ancient and Greek Ideas about the Solar System

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Ideas About the Solar System From Prehistoric Ti
mes
to Ptolemy
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Ancient Ideas about the Solar System

• Prehistoric -27,000 Bone chips w/phases of the
  moon markings.
  
• Stonehenge GB, Medicine Wheel Wyoming, Mayan and
  Aztec temples Stone alignment points to sunrise
  at Summer solstice lunar Venus rises.
  

Built ca 3100-2300 BCE
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Jupiter
Mercury
Venus Saturn Mars
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• Stonehenge was built in three stages
• 3100 BCE - A wooden post circle surrounded by
• a ditch ( the Aubrey Holes)
• 2500 BCE - Bluestones from 245 miles away.
• 2300 BCE - Still larger stones from 20 miles
  away
  
• (the Saren stones) with lintels across the top.

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What are the observations that we
(the Greeks) are trying to explain?

• The stars (constellations) change throughout the
  year -
  
• they move slowly westward.
• The planets move against the background of the
  stars
  
• and sometimes exhibit retrograde motion.
• The sun move across the sky from east to west
  daily
  
• (diurnal motion).
• The moon appears at different locations in the
  sky
  
• and goes through phases every 29.5 days.
• The seasons go through their cycle once per year.

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Greek Ideas about the Solar System

• Thales 600 BCE knew about the ecliptic, phases
  of the moon, and the length of the year and the
  seasons.
  
• Pythagoras 550 BCE (mathematics) - Taught that
  the earth, moon and other heavenly bodies were
  divine, perfect spheres and their orbits were
  concentric spheres that made music that only
  gifted ears could hear.

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Greek Ideas about the Solar System cntd.

• Philolaus 500 BCE The Earth and the other
  planets moved in a circular path around a
  central fire which was not the Sun. The sphere
  carrying the stars did not move, however.
• Plato 400 BCE Argued that the most perfect
  form was a circle and this led later astronomers
  to try and fit the orbits to uniform circular
  motion.
• Eudoxus of Cnidus (student of Plato) 350 BCE
  Developed a system of 27 nested spheres in
  uniform circular motion to produce a mathematical
  description of the universe. He had the
  inclinations and rates of rotation included in
  the model. He did very well quantitatively.

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Greek Ideas about the Solar System cntd.

• Aristotle 350 BCE Taught that the Earth is at
  the center of the universe and added 56
  concentric crystalline spheres carrying the
  planets and stars. He understood the phases of
  the moon.
• He considered the possibility that the earth
  rotates about sun but argued that the relative
  positions of the stars would shift as the earth
  moved along its orbit (stellar parallax). Since
  he did not see any such motion, he rejected the
  idea that the earth orbits the sun.
• He also considered the rotation of
• the Earth but rejected this as well.
• Why couldnt Aristotle
• see any parallax?
• Why did he reject
• the idea of rotation
• of the Earth?

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The Pre-Copernican (Aristotles) Earth-centere
d
Universe
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Greek Ideas about the Solar System cntd.

• Aristarchus of Samos 300 BCE Suggested that
  the Earth rotated on its axis and revolved about
  the Sun and he proposed an ingenious scheme for
  determining the distance from the earth to the
  moon and sun. His writings were apparently lost!
• Hipparchus 150 BCE Made great contributions to
  trigonometry, made the first star catalog,
  discovered the precession of the equinoxes and
  calculated the length of the year to within 6.5
  minutes! But most important for us, he developed
  a scheme where the Sun and Moon moved in small
  circle is their orbits around the Earth.
  (Ptolemy borrowed heavily from Hipparchus.)

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Ptolemys Ideas about the Solar System

• Ptolemy 150 Following Aristotle and
  Hipparchus, Ptolemy developed a model of the
  universe that was Earth-center (geocentric). He
  struggled to incorporate retrograde motion by a
  system of circles within circles - called
  epicycles. He devoted most of life to this model
  and it became the gold standard model of the
  universe for 1500 years.
• He wrote a book later translated
• by Islamic scholars - Almagest.

http//www.astronomynotes.com/history/epicycle.htm