Ancient Cosmology and Planetary Motions

Question 1

Observed motions of the planets

Answer 1

• Diurnal Motion: daily motion from East to West cause by Earth counter-clockwise rotation.
  Prograde Motion: apparent “wandering motion from WEST TO EAST wrt to “fixed” stars
• Retrograde Motion: apparent “wandering” motion from EAST TO WEST wrt to “fixed” stars

Question 2

Geocentric Cosmology

Answer 2

Explained by Aristotle, Hipparchus, 7 Claudius Ptolemeus. It showed a Earth centered model of the universe to explain and understand the physical universe.

Question 3

Heliocentric Cosmology and it’s Implications

Answer 3

• Aristarchus of Samos proposed a Sun centered model of the universe. This claimed that the planets including Earth moved in orbits around the Sun. Accepting this model was going against the Church’s doctrine and was considered heresy.

Question 4

Geometry and terms of the Copernican Model

Answer 4

• Having a Sun centered model allowed for planets to be described in the correct distance order from Sun & Retrograde motion was explained simply.

Question 5

Synodic period

Answer 5

Period it takes to complete one cycle of phases; new moon to new moon; LUNAR MONTH = 29.5 days

Question 6

Sidereal period

Answer 6

Moon’s true orbital period = 27.3 days. How long it takes moon to revolve back to same spot relative to “fixed” stars

Question 7

Contrasts between geocentric and heliocentric cosmologies?

Answer 7

• Geocentric: Earth is the center of the universe, all planetary objects circle it. Based off apparent motions and hierarchy created from religion.
• Heliocentric: Earth revolves around sun along with other planets