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INTRO TO ASTRO
Lesson 4: The Revolution
CHALLENGE OF THE DAY
Prove it activity!
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Movie Debrief
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David Christian tells us why stories change. Can you
think of a time when you changed a story because of
new information?
Can you understand why Ptolemy saw the Earth as the
center of the Universe based on what you can see of
the Sun, the Moon, and the stars?
What major shift occurred with the Copernican view of
the Universe?
HOW DO WE KNOW WHAT
WE KNOW?
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We know these things to be true now, but
how did people know 2,000 years ago?
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It is important to review the proof, the
science and the evidence that has gotten
us to our present understanding
SCIENTIFIC REVOLUTIONS
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What does progress look like?
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Science goes through a process, claims
are forwarded, defended, refuted, even
died for
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The great minds of astronomy made these
accomplishments on their own through
hard work, pain, and meticulous learning
HOW DO WE KNOW THE
EARTH IS ROUND?
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Aristotle: Studied a lunar eclipse and the
shape the shadow of the earth made on
the moon
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What shape does it make?
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How does that provide evidence for a
spherical earth?
CONTINUED
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Aristotle also made a very keen
observation of a ship sailing away towards
the horizon
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What happens?
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How does this provide evidence?
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Picture of sailing ship
CONTINUED
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When Aristotle traveled he noticed that
you can see different star
constellations in different places
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Would this be possible if the earth was
flat?
ERATOSTHENES
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Video
HOW DO WE KNOW THE
EARTH REVOLVES AROUND
THE SUN?
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Aristarchus: 280 BC
ARISTARCHUS
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Did measurements using
trigonometry concluding that the Sun
is much larger than the earth
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Also observed that the stars don’t
move, this could be evidence in favor
of geocentrism, but Aristarchus
didn’t think so
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Parallax, instead the stars a very far
away
PTOLEMY
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2nd century, Ptolemy came up with a model of the
solar system that had the earth at the center
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He mapped the known the planets, calculated the
time it took them to orbit the earth
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His model was the accepted model of the solar
system for almost 1,400 years
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It was wrong but was it bad science?
MOTION OF THE PLANETS
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Geocentrists: We see the planets move
across our sky, and we stand still.
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The planets must be orbiting around us!
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How do we know the difference between
the planets and the stars?
RETROGRADE MOTION
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The planets move continuously across our sky,
but at some point, something very weird
happens
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They start to move backwards for a period of
time
Why?
This was the central mystery of astronomy for
many centuries
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RETROGRADE MOTION
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Ptolemy offered an explanation to this
phenomena in his model
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http://astro.unl.edu/classaction/animations/rena
issance/ptolemaic.html
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It was wrong, but was it bad science?
ANOTHER MODEL APPEARS
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Not until the 1500’s did Ptolemy’s
model get challenged, and it did by an
astronomer named…
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Nicolas Copernicus
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Made official claims that were being
put forth since Aristarchus
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http://astro.unl.edu/classaction/animations/renaissance/retro
grade.html
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http://astro.unl.edu/classaction/animations/renaissance/ptole
maic.html
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http://astro.unl.edu/classaction/animations/renaissance/venu
sphases.html
COPERNICUS
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Copernicus provided a radical model of the solar system,
one that placed the SUN at the CENTER
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He, like Ptolemy, provided calculations for the orbits of the
planets, the seasons, and the solstices
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He even offered an explanation for why the planets move
backwards
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http://astro.unl.edu/classaction/animations/renaissance/retro
grade.html
THE CHURCH
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The Catholic Church, the primary
political and social power at the
time, did not like Copernicus’ idea
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Why? Ideas?
THE CHURCH
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The Scriptures say that the earth is,
and shall forever be, “unmoved”
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By taking the earth out of the center of
the solar system, it makes our role in it
seem less important, less “central”
GALILEO
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The dawn of the telescope!
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Article