Chapter 3 with a little help from Chapter 2
(The History of) the Science of Astronomy
29 1/2 days to go through the cycle
some calendars based on the lunar cycle
Earth's orbit around the Sun, tilt, seasons
direction of Sun at winter and summer solstices
Sun's track across sky during day
some ancient architecture was set up for the Sun's cycle
sunrise on the Summer Solstice at Stonehenge
Ocmulgee Earth Lodge ner Macon:
door to Earth Lodge
top view of Earth Lodge -- door at ~116 degrees from north, i.e., winter solstice sunrise
Chaco Chanyon Sun Dagger:
winter Solstice (noon) from Navaho website www.lapahie.com
summer Solstice (noon)
knowing time of year was useful for scheduling crop plantings
can determine the time of day from the position of Sun in sky
(figure repeat)
constellations drift across sky during night 8pm midnight
Ancient people used the cycles of the Sun, Moon, and constellations
in order to create calendars and determine the time of day or night
first known use of conceptual astronomical models without divine intervention
Anaximander (610 - 546 BC):
Geocentric Universe and Celestial Sphere
Aristotle (384-320 BC):
lunar eclipses show that the Earth is round
Eratosthenes (276 - 194 BC):
estimates size of Earth
Plato (428 - 348 BC) asserted Sun, Moon, stars move in perfect circles
although they already knew that some planets showed retrograde motion
Eudoxus (400 - 347 BC) solution:
simplified diagram b
simplified diagram c
refinements:
Apollonius (240 - 190 BC)
Hipparchus (190 - 120 BC)
Ptolemy (100 - 179 AD) worked out the math, predicted positions of
planets in future, published predictions ==> called Ptolemaic model
recording the Greek ideas
The Sun-centered (heliocentric) model of
Aristarchus (310 - 230 BC) hadn't caught on
Ptolemy's geocentric model and later calculations were used through the middle ages
Nicholas Copernicus (1473 - 1543 AD) again proposed Sun-centered model
This explained retrograde motion:
diagram
very accurate "naked eye" observations
did not see angles between stars change
thought that the planets orbited the Sun which orbited the Earth
observed a "new star" in 1572
Johannes Kepler (1571 - 1630 AD):
Kepler's laws of planetary motion: #1,
#2, #3
Galileo Galilei (1564 - 1642 AD) argued for a heliocentric model
Objects in motion remain in motion unless affected by a force
Parallax might be too small to see
Observed all phases of Venus, which is possible in
heliocentric system
but not in
geocentric system
Winning point: Kepler's model predicted planetary motion more accurately
Science makes progress by:
new observations -- Galileo saw Jupiter's moons through telescope
intuition
(idealized) Scientific Method
signs of pseudo-science
scientific theories
rarely makes specific predictions
predictions don't match observations any more often that random chance predicts
no physical correlation between human events and planets and stars
gravitational effects are miniscule
constellations are accidental alignments of stars at various distances
