Download CHAPTER 26

CHAPTER 26
26.2 OBSERVING THE SOLAR
SYSTEM: A HISTORY
THE MOVEMENTS OF PLANETS
AND STARS
• GEOCENTRIC
MODEL
• EARTH CENTERED
MODEL
• USED TO EXPLAIN
PLANETARY
MOTION
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
March
Feb.
Jan.
Dec.
April
Sept.
May
Aug.
East
June
July
West
Retrograde
motion of
Mars
PTOLEMY
GEOCENTRIC MODEL
• DEVELOPED FIRST
MODEL THAT
COULD PREDICT
PLANET MOTIONS
HELOCENTRIC MODEL
• CREDITED TO
POLISH
ASTRONOMER
NICOLAUS
COPERNICUS (1473
-1543)
• SUN CENTERED
MODEL
• BASIS FOR
MODERN
UNDERSTANDING
OF UNIVERSE
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
YouTube - Retrograde Motion and
the Opposition of Mars
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
JOHANNES KEPLER
• THEORIZED
PLANET’S ORBITS
TO BE ELLIPTICAL
• DEVELOPED THREE
LAWS THAT ARE
THE FOUNDATION
OF CELESTIAL
MECHANICS
KEPLER’S 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 IT’S
ORBIT
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
Earth’s orbit
January 15th
Equal areas
June 15th
(30 days)
July 15th
(30 days)
Sun
December 15th
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.
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
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