Transcript Models of Our Solar System

Models of Our Solar
System
A Study in Developing a Scientific
Model
Scientific Models
We know that science is done using the
Scientific Method, which includes the
following steps :
Recognize a Problem
Form a Hypothesis
Predict Consequences of the
Hypothesis
Perform an Experiment to test
Predictions
Formulate the Simplest General
Rule
Scientific Models
When you formulate the simplest
general rule, you are trying to organize
your hypothesis, prediction,
experimental steps and conclusions so
that they can be communicated and
understood.
A good way to do this is to develop a
Scientific Model.
A Scientific Model is just a description
of a scientific idea.
Scientific Models
A scientific model can be a word
description.
For Example :
A star is big ball of burning gasses.
Scientific Models
A scientific model can be an actual
physical model.
For Example :
A globe.
Scientific Models
A scientific model can be a metaphor.
For Example :
Mars is like a large ball of rusting metal.
Yes, I know this is really a simile, but
give me a break.
Scientific Models
A scientific model can be a
mathematical equation.
For Example :
E = mc2
Developing a Scientific Model
REAL
WORLD
Initial Observations
or Assumptions
Model

You start with the real
world.
 You then make your
initial observations or
assumptions.
 This then leads to a
model.
 But this isn’t where
this process ends.
Developing a Scientific Model

REAL
WORLD
Initial Observations
or Assumptions
Model
Make Predictions
Based on Model
Compare
Observations to
Predictions
Once you have your
model you then can
make some
predictions based on
your model.
 Then it is time to test
your predictions by
comparing these
predictions to
observations.
Developing a Scientific Model

REAL
WORLD
Initial Observations
or Assumptions
Model
Make Predictions
Based on Model
Mathematics
Physics
Simplicity
Revise
Model
Compare
Observations to
Predictions
Were your predictions
correct or not ? If not
revise (fix) your model.
You don’t have to throw
it out.
 You revise your model
based on Mathematics,
Physics and Simplicity
(simpler is usually
better).
Developing a Scientific Model

REAL
WORLD

Initial Observations
or Assumptions


Model
Mathematics
Physics
Simplicity
Revise
Model

Make Predictions
Based on Model
Compare
Observations to
Predictions
Now you get to start
the process over
again.
And Again!
And Again!!
Don’t worry, be
happy. This is how
science is done.
Remember, science
is self-correcting.
Over time our understanding of the Solar System has changed.
It has evolved.
As our knowledge increased and our technology improved we
were able to make better scientific models of our Solar System.
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We will start around
1600 BC with the
Babylonians.
The Babylonians made
extremely detailed
catalogs of star
positions and began to
keep long-term records
of planetary positions.
By 800 BC they had
fixed the positions of
the planets compared
to the stars. These were
recorded on clay
tablets.
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By 240 BC the
Babylonians were able
to use their charts to
predict solar and lunar
eclipses.
These charts also
showed a phenomena
of planetary motion
called retrograde
motion. The apparent
backwards motion of
the planets in the night
sky.
This motion is not a true motion of the planet,
but these observations will require many
revisions of the model of our Solar System
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In ancient Greece, a
scientist by the name of
Aristotle (384-322 BC)
developed a model of
the universe (5 planets
and the background
stars).
Aristotle’s model built
on the models of
Pythagoras and Plato,
and consisted of nested
spheres (a ball within a
ball).
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Aristotle observed that
the Earth was a sphere
and consisted of objects
made of the element
Earth.
Other spheres were
centered on the Earth
and included water, air
and fire (Sun). Outside
of this were the
observed planets
(Mercury, Venus, Mars
and Jupiter. Outside of
this would be the
sphere of the stars (the
Zodiac).
Aristotle’s Geocentric Universe
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Aristotle even had a
Physics to explain the
motion of objects.
Basically motion
consisted of natural
and forced motions.
The spheres rotated
naturally, but to move
something, like lift a
rock required a force.
One problem of this
model was its inability
to explain retrograde
motion.
Aristotle’s Geocentric Universe
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The Geocentric model
persisted and other
scientists tried to refine
it so that they could
explain retrograde
motion.
One such person was
Hipparchus (160-127
BC). A Greek
astronomer
He introduced
eccentrics, epicycles
and deferents to his
models of the Solar
System.
Hipparchus
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The eccentric is a
point where the
Earth is which is
not exactly at the
center of the other
spheres.
This helped explain
the apparent
changes in speed for
the planets.
C
Eccentric
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The path around the
Earth is called the
deferent.
A planet rides along a
small circle centered at
a point on the deferent.
This path is called the
epicycle.
The planet moves along
the epicycle counterclockwise while the
center of the epicycle
moves counterclockwise along the
deferent. Watch.
Epicycle
C
Deferent
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This model didn’t
match observations as
well as we would like.
But it did allow
retrograde motion.
The major problem
was that it was too
complicated.
Remember, simpler is
better.
This didn’t stop people
from accepting it,
actually other scientists
actually added to it.
Epicycle
C
Deferent
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Claudius Ptolemy,
around AD 125, revised
the geocentric model
more.
Ptolemy first allowed
for the planets to move
in a non-uniform way.
This means they could
speed up or slow down.
But he added in a point
opposite the center
from the eccentric
which one could
observe the planets
moving in a uniform
way. This point was
called the Equant.
C E
Claudius Ptolemy
C E
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Even though this
model was
extremely
complicated it did
match observations
fairly well.
This model was
accepted for nearly
1400 years, and
there are actually
people who believe
it is true today.
C E
This was about to change !!!!!!
Enter Nicolaus Copernicus.
Copernicus’ Heliocentric
Model
 Nicolaus Copernicus
(his friends called him
Copper) (1473-1543)
developed a
heliocentric model and
distributed a copy
among his friends in
1514.
 It wasn’t until late in his
life that Copernicus
finally agreed to have
his work published.
Copernicus’ Heliocentric
Model
 All the heavenly spheres
revolve around the Sun.
 The distance from the
Earth to the sphere of
Stars is much greater
than the distance from
the Earth to the Sun.
 The Earth spins on its
axis, which explains the
motion of the planets.
Copernicus’ Heliocentric
Model
 The motion of the Sun
relative to the stars
results from the annual
revolution of the Earth
around the Sun.
 The planet’s retrograde
motions occur from the
motion of the Earth
relative to the other
planets.
Animation II
Copernicus’ Heliocentric
Model
 The Copernican model
wasn’t any better than
Ptolemy’s at matching
observations.
 But some scientists
began to accept it.
 However many,
including the church,
felt it shouldn’t be
confused with reality.
Kepler’s Heliocentric Model
 In the 1600’s Johannes
That
predictions
must match
observations.
Kepler used
astronomical data
recorded by his former
boss to develop a
heliocentric model of
our Solar System.
 To do this he applied a
condition on his model:
Kepler’s Heliocentric Model
 Between 1609 and
1618, Kepler
developed his
three Laws of
Planetary Motion.
 These are still
used today !!!!!
Law 1 : The Law of Ellipses
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The orbit of each
planet is an ellipse,
with the Sun at one
focus.
 An ellipse is like an
oval where the
distance from one
focus to a point on
the ellipse and back
to the focus is the
same.
Law 1: The Law of Ellipses
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We can tell how
close an ellipse is
to a circle by its
eccentricity.
 An ellipse with an
eccentricity of 0,
would be a circle.
 As the eccentricity
approaches 1, the
circle becomes
more elliptical.
A ellipsehas
has anan
A circle
eccentricity
eccentricity
between of
0&1
0
Law 2 : Law of Equal Areas
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A line drawn from a planet to the Sun
sweeps out equal areas in equal time.
 What this means : The farther a planet is
from the Sun the slower it moves.
Faster
orbital
speed
Slower
orbital
speed
Law 3 : Harmonic Law
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The square of the orbital period (the time it takes
a planet revolve around the Sun one time) of a
planet is directly proportional to the cube of the
planet’s average distance from the Sun.
What this means for us : The planets farther from
the Sun take longer to orbit the Sun. (Much
weaker than the above statement)
Where’s the Science ?
Each of these models, from Aristotle to Kepler had one problem.
There was no scientific reason to accept one over the other.
It took Isaac Newton, with a little help from
Galileo, to establish a central force that held the
universe (Solar System) together.
Gravity