Transcript Keplers Model of the Solar System

Bellwork
1. Who is credited with the revolutionary model
of a HELIOCENTRIC solar system?
A. Aristotle
B. Ptolemy
C. Galileo
D. Copernicus
2. The planets loop backwards in their orbits.
A. TRUE
B. FALSE
3. During which months is Earth closest to the
Sun?
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The story so far….
• Ancient Greeks had a GEOCENTRIC model of the solar
system with Earth in center and Sun and planets in
perfect circles.
• Ptolemy add many epicycles to explain the looping of
planets during retrograde motion.
• Galileo used a telescope to see phases of Venus,
Jupiter’s moons, rotating sunspots
• Copernicus made a HELIOCENTRIC model of the solar
system with the Sun in the center so the planets were
NOT looping backwards, Earth’s faster orbit was
‘passing’ the slower outer planets.
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http://www.classzone.com/books/earth_science/terc/content/investigations/es2603/es2603page01.cfm
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Kepler’s Model of the Solar
System
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Tycho Brahe (1575)
 After seeing the total eclipse on August
21, 1560, and became a master of
careful astronomical OBSERVATIONS.
 Lost part of his nose in a duel and
replaced it with a metal one.
 Made DETAILED naked eye
observations of the motions of the
planets.
 In the course of 30 years, he had
amassed the most accurate
astronomical DATA of the day
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Johannes Kepler’s (1600)
Kepler ‘inherited’ the observations after the
sudden death of Tycho
Mathmatician - Kelper's mathematical
skills were extraordinary.
He could not get Tycho's very careful
observations to fit Copernicus’ model.
He constructed 3 Laws about planets
orbits:
SHAPE, SPEED, TIME
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Kepler’s 3 Laws of Planetary Motion
1st Law: Ellipses!
The SHAPE of the orbital paths of each planet is
an ellipse (NOT a perfect circle)
(with the Sun not exactly in the center, but at one focus)
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http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600::/sites/dl/free/007299181x/787
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78/Kepler_Nav.swf::Keplers%20Second%20Law%20Interactive
2nd Law: SPEED of the planet
An imaginary line connecting the Sun to any planet
sweeps out equal areas in equal time.
Area 1
90 days
Planets have
variations in
their orbital
speed
Area 2
90 days
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Kepler’s 3rd Law:
a planet’s orbital TIME is proportional to its distance.
In other words……the farther away the planet, the longer its ‘year’
P2 (years) = A3 (AU)
1 Astronomical Unit = The Earth-Sun Distance (93 million miles)
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Kepler’s Third Law
Object
a (AU)
P (year)
a3
Mercury
0.387
0.241
0.058
=
0.058
Venus
0.723
0.615
0.378
=
0.378
Earth
1.00
1.00
1.00
=
1.00
Mars
1.52
1.88
3.51
Jupiter
5.20
11.9
141.
Saturn
9.54
29.5
868.
Uranus
19.2
84.0
7,080.
P2
=
=
=
=
=
Neptune
30.1
165.
27,300.
Pluto
39.5
248.
61,600. =
3.53
142.
870.
7,060.
27,200.
61,500.
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Heliocentric Solar System
Using data construct a model to show the correct SIZE and SCALE
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Isaac Newton (1642 – 1727)



One of the most brilliant
theoreticians to ever live.
Explained WHY the planets
move as they do.
He formulated three laws of
motion and the law of universal
gravitation.
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Newton’s 1st Law of Inertia:
Objects in uniform straight line motion continue in
straight line motion unless an outside force is
applied to change their motion
Once in orbit, a planet
will continue its orbital
motion at constant
velocity until an outside
force (asteroid, another planet?)
acts on it to change its
orbit.
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Newton’s Second Law
The ACCELERATION (change in motion) of an
object is directly proportional to the net FORCE acting
on the object, is in the direction of the net force, and
is inversely proportional to the MASS of the object.
a = Fnet
mass
OR
F = ma
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Newton’s Third Law
Whenever one object exerts a force on
a second object,
the second object exerts an
equal and opposite force on the first
object.
Forces are interacting in PAIRS – one object on another
“To every action there is an equal and opposite re-action.”
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Law of Universal Gravitation
Mass attracts mass
GM1M2
F
2
R
Gravity is the FORCE that causes objects to move!
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