PHY 113 Lecture Notes - Lecture 2: System Model, Centrism, Heliocentrism
9 Jun 2018
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Chapter 2
The Copernican Revolution
2.1 Ancient Astronomy • Ancient civilizations observed the skies
• Many built structures to mark astronomical events
Summer solstice sunrise at Stonehenge:
Spokes of the Big Horn Medicine Wheel (in Wyoming, Plains Indians) are aligned with the
rising and setting of the Sun and other stars
The image cannot be displayed. Your computer may not have enough memory to open the
image, or the image may have been corrupted. Restart your computer, and then open the file
again. If the red x still appears, you may have to delete the image and then insert it again.
This temple at Caracol, in Mexico, has many windows that are aligned with astronomical
events
2.2 The Geocentric Universe
Ancient astronomers observed:
Sun Moon Stars
Five planets: Mercury, Venus, Mars, Jupiter, Saturn
Sun, Moon, and stars all have simple movements in the sky
Planets (“wanderers”): • Move with respect to
fixed stars
• Change in brightness • Change speed
• Undergo retrograde motion
system; everything moved in circles.
Needed epicycles to work (added to the model by Ptolemy)
• Inferior planets: Mercury, Venus
• Superior planets: Mars, Jupiter, Saturn Now know:
Inferior planets have orbits between Earth and Sun
Superior planets’ orbits are farther away
Early observations:
• Inferior planets never too far from Sun
• Superior planets not tied to Sun; exhibit retrograde motion
• Superior planets brightest at opposition (opposite side of planet than the Sun)
• Inferior planets brightest near inferior conjunction (nearer the Sun and larger on the sky)
Go outside and look at the sky. It certainly seems like everything is revolving around us....
How do we know is the Geocentric Model wrong? Why do you think the Earth goes around
the Sun,
instead of the other way around?
Can you prove it? (Hint: “science says so” is not a good proof. It wouldn’t convince
Aristotle, for example.)
Perhaps a few more details of the philosophy behind the geocentric model would help. The
Aristotelian view of the universe held that:
• Earth is corrupt, subject to decay
• Spheres and Circles are “perfect shapes.”
• Heavenlybodiesareperfectspheres
• Heavenlybodiestravelinperfectcircles • Everything goes around the Earth
• IfEarthmoved,whydon’twefeelit?
• IfEarthmoved,wewouldseeparallaxtostars!
Can you disprove this model?
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
2. 1 ancient astronomy ancient civilizations observed the skies: many built structures to mark astronomical events. Spokes of the big horn medicine wheel (in wyoming, plains indians) are aligned with the rising and setting of the sun and other stars. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. This temple at caracol, in mexico, has many windows that are aligned with astronomical events. Sun, moon, and stars all have simple movements in the sky. Planets ( wanderers ): move with respect to fixed stars: change in brightness change speed, undergo retrograde motion system; everything moved in circles. Needed epicycles to work (added to the model by ptolemy: inferior planets: mercury, venus, superior planets: mars, jupiter, saturn now know:
