Ancient Astronomy

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Ancient Astronomy
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Early Greeks - 6000 years ago
Plato
Aristotle
http//www-groups.dcs.st-and.ac.uk/history/Mathem
aticians/Plato.html
http//www-groups.dcs.st-and.ac.uk/history/PictDi
splay/Aristotle.html
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Relied only observational data
The Greeks used philosophical arguments and logic
to explain natural phenomena
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Observation 1. Star Movement
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(No Transcript)
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Observation 2. Earths Shape.
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The Earth must be a sphere
The Sphere is the ideal shape.
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Observation 3. Planet Movement
Backwards movement
Change in brightness
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All the planets moved in perfect spheres/ circles.
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Another Greek Aristarchus
The sun as the center idea was quickly
forgotten for almost 2000 years
- Profess that the sun was the center of the
universe
- Based his idea on measurements that the sun was
much further away than the moon.
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What could they not explain?
1. Changes in Brightness of planets
2. Backwards movement of the planets
Be sure to watch the entire movement of the
object.
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Another Greek Ptolemy
2nd century AD - Egypt
Developed a geocentric model that accounted for
those unexplained observable motions of planets.
Book - the "Almagest" (literally, "The Greatest")
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The backwards movement was first explained as
follows the planets were attached, not to the
concentric spheres themselves, but to circles
attached to the concentric spheres, as
illustrated in the animation. These circles
were called Epicycles, and the concentric
spheres to which they were attached were termed
the Deferents.
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"Epicycles"
- Still the perfect circles
- Different Brightness
- Backward movement
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Geocentric Model
CHECK THIS OUT Aristotle's Universe A
Geocentric Model
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Enter an old but new MODEL!!
Until the 16th century - the geocentric model was
used
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Copernicus
1473-1543 - Poland
He proposed that the Sun, not the Earth, was the
center of the Solar System.
Book - On the Revolutions of the Heavenly Bodies
http//www-groups.dcs.st-and.ac.uk/history/PictDi
splay/Copernicus.html
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One believer in this model was burned at the
stake.
The Copernicuss Book was published on his
deathbed.
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The planets in such a geocentric system naturally
vary in brightness because they are not always
the same distance from the Earth.
The backwards motion could be explained in terms
of geometry and a faster motion for planets with
smaller orbits. Check this out - Retrograde
Motion
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Heliocentric Model