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13 Cards in this Set

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Scientific method
form hypothesis, based on observations, experiments and existing laws-> test hypothesis, make predictions->hypothesis gains stregnth, revised
apparent shift of a nearby object, relative to background objects, due to changing position of observer

from earth, stars appear to shift relataive to background stars

farther away=smaler parallactic shift
retrograde motion
planets appear to move eastward relative to stars, every once in a while reverse direction and move westward
physical laws govern universe
earth is @ center of finite universe, earth is imperfect

proved earth was spherical
models of planetary motions based on concept of epicycles, to explain retrograde motion
planets orbit on circles, which are tied to larger circles
mercury & venus tied to Earth-sun line
Motion of planets around sun (heliocentric)
Retrograde motion occurs when inner planet passes outer planet
Uniform circular motion (epicycles to explain small variations in motion)
Model w/ planets orbiting the sun, but the sun orbiting Earth
designed intruments
discovered new star (supernova)
adopted heliocentric view
3 laws of planetary motion using Brahe's observations
Kepler's first law
Each planet moves in an elliptic orbit with the sun at 1 focus of the ellipse
Keplers second law
Line from sun to any planet sweeps out equal areas of space in equal time intervals
Move faster when closer to sun
Keplers third law
the squares of the planets are proportional to the cubes of their average distances from the Sun



planets closer to sun: a is smaller, so P is smaller

planets further from sun: a is larger, so P is larger
Newtons law of universal gravitation
gravity causes acceleration, which causes gravitation force

gravity keeps planets orbit around sun, moon around earth