1. Motions of Planets in the Sky
a. Planets = Wandering stars in Greek
b. Why did the ancient Greeks reject the real explanation for planetary motion and
what was so mysterious about motion in sky
c. Whats so mysterious
i. Planets usually move eastward from night to night, but sometimes they go
westward for a few weeks
ii. We see retrograde motion when we pass by a planet. Basically when we
overtake a planet, it appears to move back for a bit then go forward.
d. Parallax- the apparent shift of the position of an object
e. Greeks knew that the lack of observable parallax to the naked eyes means one of
two things.
i. Stars are so far away that the stellar parallax is too small to notice
ii. Earth does not orbit the Sun. if is the center of the universe
f. They believed 2 bc they didn’t think stars could be that far away
2. Examples of Ancient Astronomy
a. People knew how to mark seasons long ago
i. Stonehenge by marking where the sun rise and set
b. Ancient Aztecs had temples which marked when the equinox was cus their
temples faced due east
c. Sun Dagger in Southwest US to mark summer solstice
d. Sundials tracking time, navigation, astrology
e. Ancient Greek Astronomy
i. Making models of nature or modeling
ii. Scientific method- developed by greeks
iii. Observe, Model, Predict
iv. Achievements of Ancient Greeks
1. Realized that the earth was round as curvature of earths shoadow
on the moon
2. Figured Earths size forom the suns position
v. Most important contribution: Geocentric model
1. Earth at the center
vi. Ptolemy made the most sophisticated geocentric model. Almagest which
was accurate enough to be used for 1500 yrs
3. The Copernicus Revolution
a. Main people
i. Copernicus, Tycho, Kepler, Galileo
ii. Copernicus (1473-1543)
1. Priest who proposed Heliocentric model to determine layout of the
solar system.
2. Bro sold his book on his deathbed
iii. Tycho Brahe (1546-1601)
