1. CHAPTER 26 26.2 OBSERVING THE SOLAR SYSTEM: A HISTORY

2. THE MOVEMENTS OF PLANETS AND STARS GEOCENTRIC MODEL EARTH CENTERED MODEL USED TO EXPLAIN PLANETARY MOTION

3. 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 Retrograde motion of Mars EastWest Sept. Aug. July June Dec.Jan.Feb.March April May

4. PTOLEMY GEOCENTRIC MODEL DEVELOPED FIRST MODEL THAT COULD PREDICT PLANET MOTIONS

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

6. 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

7. YouTube - Retrograde Motion and the Opposition of Mars

8. TYCHO BRAHE 16 TH 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

9. JOHANNES KEPLER THEORIZED PLANET’S ORBITS TO BE ELLIPTICAL DEVELOPED THREE LAWS THAT ARE THE FOUNDATION OF CELESTIAL MECHANICS

10. KEPLER’S LAWS OF PLANETARY MOTION 1 ST 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 IT’S ORBIT

11. 2 ND 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

12. June 15th July 15th January 15th December 15th (30 days) Sun Equal areas Earth’s orbit KEPLER’S EQUAL AREA LAW states that a line connecting Earth to the sun will pass over equal areas of space in equal times. Because Earth’s orbit is elliptical, Earth moves faster when it is nearer to the sun.

13. 3 RD 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 P 2 = D 3 –P = PERIOD –D = DISTANCE

14. 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