Ancient Astronomy

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Ancient Astronomy

• Astronomy the most ancient of the sciences
• Astronomical records back to prehistoric times

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Scientific Methods Common Steps

1. Recognize a question, a puzzle, or an unexplained
   fact.
2. Make a hypothesis (educated guess) to resolve the
   puzzle.
3. Predict consequences of the hypothesis.
4. Perform experiments or make calculations to test
   the predictions.
5. Formulate the simplest general rule that
   organizes the three main steps.

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The Scientific Attitude

• The scientific attitude is one of
• inquiry.
• experimentation.
• willingness to admit error.

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The Scientific Attitude

• Scientists
• are experts at changing their minds.
• must accept experimental findings
• test for erroneous beliefs
• understand objections and positions of
  antagonists.

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The Scientific Attitude

• Fact is a close agreement by competent observers
  who make a series of observations about the same
  phenomenon.
• A scientific hypothesis is an educated guess that
  is only presumed to be factual until supported by
  experiment.

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The Scientific Attitude CHECK YOUR NEIGHBOR

• Which of these is a scientific hypothesis?
• The Moon is made of green cheese.
• Atomic nuclei are the smallest particles in
  nature.
• A magnet will pick up a copper penny.
• Cosmic rays cannot penetrate the thickness of
  your textbook.

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The Scientific Attitude CHECK YOUR NEIGHBOR

• Which of these is a scientific hypothesis?
• The Moon is made of green cheese.
• Atomic nuclei are the smallest particles in
  nature.
• A magnet will pick up a copper penny.
• Cosmic rays cannot penetrate the thickness of
  your textbook.

Explanation All are scientific hypotheses!
All have tests for proving wrongness, so they
pass the test of being a scientific hypothesis.
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Oldest star chart- 32,000 years ago (Orion?)
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Stonehenge 3100 2100 BC
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Great Pyramid at Khufu (Cheops) 2600
B.C. Aligned within 1/20 degree of true
north Possible correlations with astronomical
objects?
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Chichen Itza Mayan observatory
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Medicine Wheel Northern Wyoming
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Chaco Canyon supernova of 1054?
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Chaco canyon Anasazi sun dagger A.D.
400-1300, marks summer solstice
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Constellations
Apparent groupings of stars relatively fixed
positions
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Constellations the 88 semi-rectangular regions
that make up the sky
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Star trails
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Star trails around South Celestial Pole (Gemini
Observatory, Chile)
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Most of modern astronomy and cosmology comes from
the Greeks
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Celestial Sphere

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The Geocentric View

• Aristotles View The Most Perfect Form is the
  Circle
• The Crystalline Spheres

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The Motion of the Earth
Correct Method - Wrong Conclusion

• Parallax The apparent motion of an object due
  to the motion of the observer.
• The Greeks could not detect any parallax for the
  stars (or planets).
• Conclusion
• The Earth is not moving.
• OR
• The Stars are too far away to measure parallax
  with crude instruments / eye.
• The Greeks chose not moving.

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Aristarchus 310 - 230 BC

• Heliocentric model
• Determined relative distances between
• Sun and Moon

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The Distance to the Sun
Aristarchus of Samos 310 - 230 BCE

• Aristarchus measured ? to be 87 degrees
• Sun Distance 19 Moon Distance
• (today Sun is about 400 times further away than
  moon)

First Quarter Moon
Third Quarter Moon
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Ptolemy (85 165 A.D) Lived in Egypt, probably
Alexandria Summarized Greek astronomy in the
Almagest Geocentric model of solar system
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Epicycles and Equants
Everything circles something else
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Very complicated but it worked! (sort of)
http//astro.unl.edu/naap/ssm/animations/ptolemaic
.swf
http//astro.unl.edu/animationsLinks.htmlca_renai
ssance
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Major assumptions of the Ptolemaic model

• All motion in the heavens is uniform circular
  motion.
• The objects in the heavens are made from perfect
  material, and cannot change their intrinsic
  properties.
• The Earth is at the center of the Universe.

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After the Greeks

• Alexandria burns in 272 A.D., Roman empire
  collapses, and Europe enters Dark Ages
• Roman Catholic Church combines Ptolemaic with
  Aristotelian thought into official church
  doctrine Earth as immovable center of cosmos
• Much of astronomy is carried forth by Persian and
  Islamic astronomers who preserved Greek thought
  and refined it named many stars we know today

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Breaking through the old model
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Major problems with the Ptolemaic SystemIt
failed to.

• Accurately predict eclipses (off by hours, days,
  etc)
• Predict position of planets accurate enough
• Couldnt explain meteors, comets, supernovae

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Nicolas Copernicus (1473-1543) proposed
heliocentric hypothesis, mostly on philosophical
grounds
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Copernicus model

• Gave similar predictions to Ptolemaic model, also
  used epicycles, etc
• Proposed earth rotates on axis to cause night
  and day
• Proposed earth and other planets travel around
  sun
• Radical idea for time this sounded crazy to most
  people!!!

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De Revolutionibus Orbium Coelestium, 1543 (On
the Revolutions of the Heavenly Spheres)
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Copernicus explanation of retrograde motion
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Galileo
1564 - 1642

• All bodies fall at same rate!! - Tower of Pisa

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Galileos Telescope

• Galileos telescopic observations led him to
  firmly reject the geocentric model.

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The Milky Way was composed of millions of stars.
He realized that wherever he looked, he saw
more and more stars
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SaturnGalileo noticed.Saturn has ears
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SunspotsA. The surface of the Sun was imperfect.
B. apparent motion of the spots across the
Sun's disk implied rotation.
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• Detailed moon drawings the moon is not a smooth
  sphere!

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The Galilean Satellites

• They Orbit Jupiter!
• So Why Cannot the Planets Orbit The Sun

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The Phases of Venus Galileo noticed that when
Venus wanes (becomes crescent), it becomes larger.
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The Phases of Venus