Download Astronomy History of Ancient Models

Summarizing some Key Astronomy Historical Ideas
Cavepeople: looking at the night time sky, grunting
Greeks: (ideas from Aristotle)
1. Earth at the center of the universe.
2. Concentric spheres rotated around the earth, one with the fixed stars, one for
mars, etc.
3. Motion in the sky follows perfect harmony.
4. Objects in the sky follow perfect circular motions at constant speed.
5. Materials in the sky were different than those on earth.
Ptolemy (Roman Egyptian AD 90-168 , Earth centered model – geocentric)
1. Used the ancient greek ideas but tried to develop a more accurate geometry to
describe the motions of the “wanderers.”
2. The “Wanderers” were planets that appeared to move “differently” than the other
lights.
3. Created the geometry using epicycles to account for the strange motion of Mars &
other wanderers.
4. Epicycles were circles which rotated on circles.
5. Ptolemy’s model fit the religious views that the earth must be at the center of
everything (created by God) & followed many of the same ideas as the ancient
Greeks (perfect circles, uniform speed, materials in the sky were different than
stuff on the earth).
Copernicus: (Polish Scientist 1473-1543 , Sun Centered Model – heliocentric)
1. Believed that a simpler model could be created by moving the Sun to the center of
the universe.
2. Still used epicycles, but his model was much simpler than Ptolemy’s. Fewer
epicycles and shifting the sun to the center made the whole system less complex.
3. Believed the simplicity of his model was still “God like”.
4. His sun-centered system not widely accepted, especially by the church and
religious leaders
Tycho Brahe: (Danish Nobleman & Astronomer 1546-1601)
1. Built an astronomy center and collected data which was much more
accurate than any other prior data.
2. Data used by Kepler to plot the orbit of mars.
Johannes Kepler (German Mathematician 1571-1630)
1. Used Tycho’s data to plot the orbit of Mars and other “wanderers”
2. Found that Mars’ orbit is actually elliptical, not circular
3. Mar’s speed changes as it moves in orbit.
4. Developed 3 laws which to this day are still valid.
a. Law 1: Planets travel in ellipses (not circles).
b. Law 2: Planets sweep out equal areas in equal time (must change
their speed)
c. Law 3: The law of Periods: The Further away a planet it, the
longer it takes to make a rotation.
5. Believed in Copernicus model and that there must be some action that is
causing orbital motions
Galileo (Italian Physicist, 1564 – 1642)
1. Law of falling bodies, all objects on earth fall with acceleration g = 10
m/s/s
2. Developed many of the ideas of mechanics, experiments on earth.
3. Strongly believed in Copernicus idea of a heliocentric model of the
universe, went to “jail” (house arrest) for his views.
Newton (English Scientist, 1643 – 1727)
1. Developed laws of motion
2. Made a connection between the motion of the moon and the falling apple
on the
Earth.
3. Developed the idea of Universal Gravitation, the reason the moon moves
in an orbit is the same reason the apple falls on the earth.
4. Ties the same rules on earth to those in the heavens.
5. Generally believed to be one of the greatest scientists ever, if not the
biggest. (calculus, gravitation, optics, materials, etc, astronomy, laws of
motion)