From Aristotle to Newton

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From Aristotle to Newton
The history of the Solar System (and the universe
to some extent) from ancient Greek times through
to the beginnings of modern physics. Where do we
put the other planets in our picture of the solar
system? What are some reasons that the
geocentric model of the universe seems to make
intuitive sense?
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What are some reasons that the geocentric model
of the universe seems to make intuitive sense?

• It doesn't feel like we are moving wouldn't
  there be a wind or something?
• Why would things fall down and not towards the
  center of the universe?
• Why don't we see stellar parallax?

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Geocentric vs. Heliocentric Models of the Solar
System
Ancient Greeks knew of Sun, Moon, Mercury, Venus,
Mars, Jupiter and Saturn.

• Aristotle vs. Aristarchus (3rd century B.C.)?
• Aristotle Sun, Moon, Planets and
  Stars rotate around fixed Earth.
• Aristarchus 1st Heliocentric model
• Aristotle But there's no wind or
  stellar parallax. Doesnt feel like
• we are moving. Actually orbiting sun at
  70,000 mph!
• Difficulties with "Geocentric" model
• - Retrograde motion of planets
• - Phases of Venus

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Aristarchus
- Written in the second century BCE he
calculated the ratio of the distance between the
Earth and Sun to that between the Earth and the
Moon. (His estimate was more than an order of
magnitude too small, but the fault was in his
lack of accurate instruments rather than in his
method of reasoning.) -This image compares the
line subtending the arc dividing the light and
dark portions of the Moon in a lunar eclipse with
the relative diameters of the Moon and Sun.
-Aristarchus also found an improved value for
the length of the solar year.
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Planets sometimes appear to loop back -
retrograde motion Loops are called "epicycles"
Apparent motion of Mars against "fixed" stars
Mars
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July

Earth

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January
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Geocentric Model(Earth Centered)?

• Fairly good agreement with retrograde motion of
  planets
• Some predictive power
• More precise measurements showed errors

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Ptolemy's geocentric model (A.D. 140)?
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Heliocentric Model
Rediscovered by Copernicus in 16th century.
Much simpler was the main attraction for
Copernicus. Explains retrograde motion.
Put Sun at center of everything, but still
insisted on circles, thereby retainig unnecessary
complexity. Opposed by Catholic
Church Copernican revolution critical
realization that Earth is not at the center of
the universe, only accepted after his death.

Copernicus 1473-1543
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Galileo (1564-1642)?, Experimentalist
Built his own telescope. Discovered four moons
orbiting Jupiter. What does this
suggest? Discovered sunspots. What might we
infer about the Sun from these observations? Obse
rved phases of Venus.
Was imprisoned for the last 9 years of his life
for his scientific discoveries.
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Heliocentric model easily accounts for phases of
Venus
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Geocentric model fails to account for phases of
Venus
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The Scientific Method

• Geocentric model abandoned because of its
  failure, and to a lesser extent because of its
  complexity.