Heliocentric model of the
solar system
Reading: Unit 11
Copernicus
Galileo
Ptolemy’s
geocentric
model
Endured for nearly 1400 years!
Ockham’s razor
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All things being equal, the simplest
solution tends to be the best one
Nicolaus Copernicus (1473-1543)
Heliocentric model
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All orbits are circular
Sun is at the center
Stars do not move
(with respect to each
other)
Scientific method
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Observe phenomenon
Hypothesize cause (how?)
Predict outcome
Test outcome
Not established until 17th century!
Galileo Galilei (1564-1642)
Galileo did some really cool stuff
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Built his own telescopes!
Found 4 moons around Jupiter
The Milky way was composed of stars
Found mountains on the moon
Observed sunspots
Saw phases of Venus
Phases of Venus
The Ptolemaic and Copernican models
make very different predictions about the
phases of Venus.
U. Tenn. Physics & Astronomy Dept.
Phases of Venus
Galileo’s drawings of the phases of Venus
Phases of Venus
Starry
Messenger
Sunspots, and the Moon
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What do these have to do with the
Copernican or Ptolemaic models?
Apparently nothing, but...
The philosophy that went with the Ptolemaic
system expected the Sun, moon, planets
and stars to be perfect.
Heavenly bodies were expected to be
entirely different in character from Earth.
Sunspots, and the Moon
Armagh Observatory
António Cidadão
The “Galileo Affair”
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Galileo the pope that the heliocentric
model was correct
(He had to take it back)
Home arrest for many years
Heliocentric model
Tycho Brahe (1546-1601)
Famous for his accurate observations
of the motions of the planets.
Brahe Planetarium
Tycho’s model
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Sun orbits Earth
Other planets orbit
Sun
Summary
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Copernican model
Galileo’s evidence
Tycho
Team Activity #14
Phases of Venus
Draw sketches (top then
bottom) on page 211 before
answering question #1!!
Pick up a review sheet