Chapter 3

The History of the Science of Astronomy


Ancient Astronomical Knowledge

Ancient people used the cycles of the Sun, Moon, and constellations
                    in order to create calendars and determine the time of day or night

Direction to Sun Varies with Time and Season

Stonehenge (You Tube, looped)

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

Stonehenge's floorplan

sunrise on the Summer Solstice at Stonehenge

Chaco Chanyon Sun Dagger:
                    placement of rocks
                    diagram of Sunlight through rocks
                    Sun Dagger at noon on Summer Solstice
                    Sun Dagger at noon on Winter Solstice
                    summer Solstice (noon)
                    winter Solstice (noon) from Navaho website

          knowing time of year was useful for scheduling crop plantings


Dividing Day or Night into smaller pieces

can determine the time of day from the position of Sun in sky (figure repeat)

constellations drift across sky during night 8pm midnight


Astronomical Models of the Ancient Greeks

          Ptolemaic Model from Espaco Astrologico (You Tube, looped)


          first known use of conceptual astronomical models without divine intervention

          Anaximander (610 - 546 BC): Geocentric Universe and Celestial Sphere

          Pythagoras (560 - 480 BC): suggested that the Earth is round

          Aristotle (384 - 320 BC): lunar eclipses show that the Earth is round

          Aristarchus (310 - 230 BC): suggested that the Earth orbits the Sun (i.e., heliocentric system)

          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

                    (movie) Mars's path on sky

          Eudoxus (400 - 347 BC) solution: rotating nested spheres
                    cause daily, yearly, and retrograde motion


                    Apollonius (240 - 190 BC): simplified diagram b simplified diagram c

                    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 Copernican Revolution

          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

          Tycho Brahe (1546 - 1601 AD):

                    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

                    Kepler's laws of planetary motion: animation

          Galileo Galilei (1564 - 1642 AD) argued for a heliocentric model

                    Telescope, Sunspots, craters on the Moon

                    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 (transit of Mercury)


The Nature of Science

Scientific Method (You Tube, looped)

Scientific Method (with captions)

Mary Chapin Carpenter "I Feel Lucky" (You Tube, looped)


          Science makes progress by:

                    new observations -- Galileo saw Jupiter's moons through telescope


                    (idealized) Scientific Method

          hallmarks of science

          signs of pseudo-science

          scientific theories


Astrology is not a science

          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