Ch. 29 Sec. 1Ch. 29 Sec. 1

Overview of Solar SystemOverview of Solar System

Early IdeasEarly Ideas Humans have watched the sky for thousands of Humans have watched the sky for thousands of

yearsyears Planets change position relative to the starsPlanets change position relative to the stars

• Easy to recognize the differenceEasy to recognize the difference Believed to be Believed to be Geocentric: Geocentric: earth centeredearth centered Copernicus in 1543 noticed a difference in Copernicus in 1543 noticed a difference in

movement of planetsmovement of planets• HeliocentricHeliocentric: Sun centered: Sun centered

Planet MotionPlanet Motion

Normal direction of planets is to the eastNormal direction of planets is to the east Occasionally a planet will move in opposite Occasionally a planet will move in opposite

directiondirection• Retrograde MotionRetrograde Motion

Kepler’s 1Kepler’s 1stst Law Law Kepler used his mentors data on planetary Kepler used his mentors data on planetary

motionmotion• Demonstrated that planets move in an ellipseDemonstrated that planets move in an ellipse• Kepler’s 1Kepler’s 1stst Law Law

Kepler’s 1Kepler’s 1stst Law Law EccentricityEccentricity

• A planets distance isn’t always the same from sunA planets distance isn’t always the same from sun• PerihelionPerihelion: Closest to sun: Closest to sun• AphelionAphelion: Furthest from sun: Furthest from sun• Measured from 0 – 1: 0 – circle / 1 - parabolaMeasured from 0 – 1: 0 – circle / 1 - parabola

Kepler’s 2Kepler’s 2ndnd Law Law

An imaginary line sweeps out from sun to An imaginary line sweeps out from sun to planet of equal area in equal amounts of planet of equal area in equal amounts of timetime• 2nd Law

Other DiscoveriesOther Discoveries

GalelioGalelio• Use 1Use 1stst telescopes telescopes• Discovered 4 moons around JupiterDiscovered 4 moons around Jupiter

NewtonNewton• Gravity: observed the orbits of planets and moonGravity: observed the orbits of planets and moon• Force is directly proportional to massForce is directly proportional to mass

GravityGravity Force of gravity grows stronger with an increase Force of gravity grows stronger with an increase

in massin mass Force of gravity grows smaller with increasing Force of gravity grows smaller with increasing

distancedistance Center of mass will be closer to the heavier objectCenter of mass will be closer to the heavier object