26.2 OBSERVING THE SOLAR SYSTEM: A HISTORY

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CHAPTER 26

• 26.2 OBSERVING THE SOLAR SYSTEM A HISTORY

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THE MOVEMENTS OF PLANETS AND STARS

• GEOCENTRIC MODEL
• EARTH CENTERED MODEL
• USED TO EXPLAIN PLANETARY MOTION

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EARLY ASTRONOMERS

• EARLY ASTRONOMERS OBSERVED THAT PLANETS MOVED
  EASTWARD ACROSS THE NIGHT SKY WHEN COMPARED TO
  CONSTELLATIONS
• FOR WEEKS THOUGH, IT WOULD APPEAR THEY MOVED
  BACKWARD RETROGRADE MOTION

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PTOLEMY GEOCENTRIC MODEL

• DEVELOPED FIRST MODEL THAT COULD PREDICT PLANET
  MOTIONS

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HELOCENTRIC MODEL

• CREDITED TO POLISH ASTRONOMER NICOLAUS COPERNICUS
  (1473 -1543)
• SUN CENTERED MODEL
• BASIS FOR MODERN UNDERSTANDING OF UNIVERSE

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RETROGRADE MOTION

• EACH PLANET ORBITS CCW AROUND THE SUN AT
  DIFFERENT DISTANCES AND SPEEDS
• EARTH MOVES FASTER THAN MARS
• THE EFFECT IS DUE TO THE EARTH CATCHING UP TO AND
  PASSING MARS

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YouTube - Retrograde Motion and the Opposition of
Mars
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TYCHO BRAHE

• 16TH CENTURY DANISH NOBLE MAN AND OBSERVATIONAL
  ASTRONOMER
• STUDIED THE MOTIONS OF THE MOON AND PLANETS
  THROUGHOUT THEIR ORBITS RATHER THAN JUST AT
  CERTAIN POINTS
• RECORDS WERE THE MOST PRECISE PRIOR TO THE
  TELESCOPE

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JOHANNES KEPLER

• THEORIZED PLANETS ORBITS TO BE ELLIPTICAL
• DEVELOPED THREE LAWS THAT ARE THE FOUNDATION OF
  CELESTIAL MECHANICS

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KEPLERS LAWS OF PLANETARY MOTION

• 1ST LAW
• PLANETS TRAVEL IN ELLIPTICAL ORBITS WITH THE SUN
  AT ONE FOCI
• BECAUSE THE SUN IS AT ONE FOCUS, THE PLANETS
  DISTANCE FROM THE SUN WILL CHANGE THROUGHOUT ITS
  ORBIT

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2ND LAW

• KNOWN AS THE EQUAL AREA LAW
• STATES A LINE CONNECTING THE EARTH TO THE SUN
  WILL PASS OVER EQUAL AREAS OF SPACE IN EQUAL
  TIMES
• MEANS PLANETS MOVE AT DIFFERENT SPEEDS BECAUSE
  OF ELLIPTICAL ORBITS. MOVE FASTER NEAR THE SUN

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3RD LAW

• HARMONIC LAW
• USED TO FIND MEAN DISTANCE TO SUN IF PERIOD IS
  KNOWN OR TO FIND PERIOD (ORBIT DISTANCE) IF
  DISTANCE IS KNOWN
• FARTHER FROM SUN LONGER PERIOD
• FARTHER FROM SUN SLOWER MOVING
• P2 D3
• P PERIOD
• D DISTANCE

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ISAAC NEWTON

• LAW OF GRAVITATION
• DEVELOPED 3 LAWS OF MOTION
• LAW OF GRAVITATION
• STATES ALL OBJECTS WITH MASS EXERT A FORCE OF
  ATRACTION ON EVERY OTHER MASS
• STRENGTH OF FORCE IS PROPORTIONAL TO EACH OF THE
  MASSES
• AND INVERSELY PROPORTIONAL TO THE DISTANCE
  BETWEEN THEM

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