~1500 to ~1700
Copernicus (~1500) Brahe (~1570) Kepler (~1600) Galileo (~1600) Newton (~1670)
The Issue: Geocentric or Heliocentric Which model explains observations the best?
Copernicus (~1500) Resurrected heliocentric model
Is solar system geocentric or heliocentric?
Both models have: Circular orbits (heavenly perfection) Uniform motion (heavens cannot change)
Both models explain observations Sun, Moon, Planets Rise in east, Set in west
Both models explain observations Retrograde motion of planets
Retrograde motion Geocentric Planets ride on epicycles Sometimes appear to move backwards
Retrograde motion Heliocentric One planet overtakes another planet. Slower planet appears to move backwards.
Brahe (~1570) Measured positions of Mars very accurately. Built excellent instruments. Used data to investigate truth. Saw a supernova! (the sky changed)
Kepler (~1600) Derived (from Brahe s data) Three mathematical laws of planetary motion.
Kepler s First Law Planets have elliptical orbits around the Sun < perihelion aphelion >
Kepler s Second Law The radius vector sweeps out equal areas in equal times. Thirty days > < Radius vector Thirty days >
Kepler s Second Law means that A planet changes speed; faster at perihelion, slower at aphelion Perihelion (faster) Aphelion (slower)
Definition needed for Kepler s Third Law Period = Time to complete one cycle Ex: Earth s period of rotation =? Ex: Earth s period of revolution =?
Kepler s Third Law Period 2 is proportional to (Radius of orbit) 3 Sometimes written as T 2 α R 3 Bigger orbit radius means more time to revolve More distant planet takes more time to revolve. More distant planet moves slower.
Kepler s Laws Also applies to objects in orbit around any central mass Satellites around Earth Star around a black hole Planet around some other star Two stars orbiting each other
Meanwhile Out in the streets Galileo (~1600) Developed and used the telescope
Moon craters Galileo observed Heavens are not perfect!!!heavens are Earth-like!!!
El Greco < 1600 Cigoli - 1622
Frontpiece of G.B. Riccioli's Almagestum Novum, 1651. Notes: Urania, Models (C s, R s, P s), R s model has Jupiter and Saturn centered on Earth, Solar scope.
Galileo observes Sunspots Heaven is not perfect!! Sun rotates
Galileo observes Moons of Jupiter Earth is not the ONLY center of motion in the heavens
Galileo observes Moons of Jupiter Take that, Aristotle! AND Hey, Aristotle. Earth can move and pull the Moon along.
Galileo observes Phases of Venus Geocentric model predicts: Crescent phase only and little size change Heliocentric predicts: All phases AND gibbous is small while crescent is large http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/phasesofvenus.htm
Newton (~1700) HOW and WHY planets orbit (and objects move)
Newton (~1700) Three Laws of Motion (Read but not on test) And The Universal Law of Gravity
Newton - Universal Gravity Every mass exerts a force on every other mass. Note the UNIVERSAL statement. F F m M
Newton - Universal Gravity F F m M Gravity always attracts Bigger mass means bigger force Bigger separation means smaller force
Newton - Universal Gravity F F m D M F G mm 2 D
Newton - Universal Gravity Side comments: Predictability, Mechanistic universe F F m D M F G mm 2 D
Newton - Universal Gravity Side comments (not on test): Predictability, Mechanistic universe Chaos theory Why gravity? F F m 1 m 2 D F G mm 2 D
- Summary Geocentric Vs. Heliocentric Five people, contributions, significance Process of science