Science!Science!

OverviewOverviewA.Definitions:

1. Scientific Hypothesis2. Scientific Theory3. Scientific Model4. Crystalline Spheres5. Epicycles6. Geocentric7. Heliocentric8. Ellipse

1.Focus2.Major/Semi-Major axis3.Minor/Semi-Minor axis

9. Orbital Period10.Orbital Velocity

OverviewOverview

B. What is Science?1. What makes a hypothesis valid?2. When does Theory become Fact?

C. Our Model of the Solar System – A history1. What are the Models?2. What Observation Broke Each Model?3. Aristotle – Crystaline Spheres4. Ptolemy – Epicycles5. Copernicus – Heliocentric Circles6. Kepler – Three Laws of orbital motion

Course GoalsCourse Goals

What is Science?What is Science?

What is modern What is modern astronomy?astronomy?

What do we know about What do we know about the Universe?the Universe?

How do we know what How do we know what we know?we know?

Why Study Science?Why Study Science?

Because we are Because we are Curious!Curious!

So we can think for So we can think for ourselves.ourselves.

Because it is our Because it is our Civic DutyCivic Duty

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A Scientific Theory is:A Scientific Theory is:

A.A. An explanation for natural An explanation for natural phenomena for which little or no phenomena for which little or no evidence yet exists.evidence yet exists.

B.B. An explanation for natural An explanation for natural phenomena that has been irrefutably phenomena that has been irrefutably proven.proven.

C.C. An explanation for natural An explanation for natural phenomena for which there is a phenomena for which there is a substantial body of experimental substantial body of experimental evidence.evidence.

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A Scientific Hypothesis is:A Scientific Hypothesis is:

A.A. An explanation for natural An explanation for natural phenomena for which little or no phenomena for which little or no evidence yet exists.evidence yet exists.

B.B. An explanation for natural An explanation for natural phenomena that has been irrefutably phenomena that has been irrefutably proven.proven.

C.C. An explanation for natural An explanation for natural phenomena for which there is a phenomena for which there is a substantial body of experimental substantial body of experimental evidence.evidence.

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A Scientific Idea becomes irrefutably A Scientific Idea becomes irrefutably “True” when:“True” when:

A.A. The central committee for scientific The central committee for scientific ideas declares its truth.ideas declares its truth.

B.B. The majority of scientists agree that The majority of scientists agree that it is true.it is true.

C.C. A successful experiment reveals that A successful experiment reveals that the idea is true.the idea is true.

D.D. Never. Never.

Scientific HypothesisScientific Hypothesis

I have a

HypothesisHypothesis!!

It’s valid because it’s

Falsifiable!Falsifiable!

Missing KeysMissing Keys

Two Hypothesis: Two Hypothesis: 1.1.Absent Minded Absent Minded 2.2.Time GnomesTime Gnomes

Which is valid?Which is valid?What is the Test?What is the Test?

Scientific TheoryScientific Theory

It’s It’s justjust a a theory!theory!

Scientific theory is not Scientific theory is not mere conjecture.mere conjecture.

Theory:Theory: A A valid valid hypothesis backed by hypothesis backed by experimentalexperimental evidence evidence..

A HypothesisA HypothesisThe heavens are The heavens are perfect and perfect and unchanging.unchanging.

~Aristotle~Aristotle

What is the Test?What is the Test?

Celestial objects are embedded Celestial objects are embedded in Crystal Spheres.in Crystal Spheres.

Each Sphere rotates around us Each Sphere rotates around us at a Fixed Rateat a Fixed Rate

Geocentric:Geocentric: A model of the Solar system A model of the Solar system with the with the EarthEarth in the center. in the center.

Scientific ModelsScientific Models

The power of a model…

Is in it’s ability to Predict!Predict!

Except…Except…The crystal spheres can’t explain The crystal spheres can’t explain

Retrograde MotionRetrograde Motion

The Ptolemaic ModelThe Ptolemaic Model

Celestial objects are embedded Celestial objects are embedded in Crystal Spheres.in Crystal Spheres.

Epicycle:Epicycle: A small circle, the center of A small circle, the center of which moves on the circumference which moves on the circumference of a larger circle at whose center is of a larger circle at whose center is the earththe earth

An Alternative ModelAn Alternative Model

Sun centered model, Sun centered model, 15431543

•Simple retrograde Simple retrograde solutionsolution

•Simple orbital Simple orbital period calculationperiod calculation

•Position Position predictions predictions stillstill inaccurate.inaccurate.Nicholas CopernicusNicholas Copernicus

Heliocentric:Heliocentric: A model of the Solar A model of the Solar system with the system with the SunSun in the in the center.center.

Scientific ModelsScientific Models

Two Models

With equal predictive power…

Which one

is True?True?

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How can we absolutely choose How can we absolutely choose between competing theories that between competing theories that make equally accurate predictions?make equally accurate predictions?

A.A. The least complex is correct. The least complex is correct.

B. B. The scientist with the most The scientist with the most prestige wins.prestige wins.

C.C. A vote is held by the Central A vote is held by the Central Science Committee.Science Committee.

D.D. There is no way to choose. There is no way to choose.

New ObservationsNew Observations

Tycho Tycho BraheBrahe

Took 2 decades worth Took 2 decades worth of naked eye planet of naked eye planet observationsobservations

Accuracy to within 1 Accuracy to within 1 minute of arcminute of arc

Johannes Johannes KeplerKepler

TheoryTheory

•A student of TychoA student of Tycho

•Studied Tycho’s dataStudied Tycho’s data

•Discovered three Discovered three empirical empirical relationshipsrelationships

•Believed CopernicusBelieved Copernicus

•Suggested that the Suggested that the Sun exerts a force on Sun exerts a force on the planets.the planets.

Kepler’s 1Kepler’s 1sstt Law Law

Orbits are ellipsesOrbits are ellipses

DefinitionsDefinitions

Orbital Period:Orbital Period: The The timetime required to complete one required to complete one

orbitorbit..

Orbital Velocity:Orbital Velocity: The The speedspeed of a planet in its orbit. of a planet in its orbit.

Kepler’s Second LawKepler’s Second LawKepler’s 2Kepler’s 2ndnd Law: Law: A line joining a planet and the Sun A line joining a planet and the Sun

sweeps out equal areas during sweeps out equal areas during equal intervals of time.equal intervals of time.

What?What?

Which is true?Which is true?A.A.Fast a Perihelion, Slow at Fast a Perihelion, Slow at AphelionAphelionB.B.Slow at Perihelion, Fast at Slow at Perihelion, Fast at AphelionAphelionC.C.Same speed Same speed

Why? Make an argument.Why? Make an argument.

Kepler’s 2Kepler’s 2ndnd Law: Law: A line joining a planet and the Sun A line joining a planet and the Sun

sweeps out equal areas during sweeps out equal areas during equal intervals of time.equal intervals of time.

Kepler’s 2Kepler’s 2ndnd Law Law

If: TIf: TPP = T = TAA

Then: AThen: APP = = AAAA

Kepler’s 2Kepler’s 2ndnd Law: What? Law: What?

And: HAnd: Hpp< < HHAA

If: AIf: APP = A = AAA

Then: DThen: Dpp > > DDAAAnd: VAnd: Vpp > V > VAA

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If all planets had the same orbital If all planets had the same orbital velocity, which would have the longest velocity, which would have the longest year?year?

A.A. Earth Earth

B. B. MarsMars

C.C. PlutoPluto

D.D. Their years would be the same Their years would be the same lengthlength

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If all planets had the same period, which If all planets had the same period, which would have the longest year?would have the longest year?

A.A. Earth Earth

B. B. MarsMars

C.C. PlutoPluto

D.D. Their years would be the same Their years would be the same lengthlength

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If all planets had the same period, which If all planets had the same period, which would have the highest orbital velocity?would have the highest orbital velocity?

A.A. Earth Earth

B. B. MarsMars

C.C. PlutoPluto

D.D. Their years would be the same Their years would be the same lengthlength

Kepler’s 3Kepler’s 3rdrd Law Law

PP 2 2 = a= a

33

a = Semi-major a = Semi-major axisaxisP = Orbital PeriodP = Orbital Period

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When must a Scientific Theory die?When must a Scientific Theory die?

A.A. When the people who believe it die. When the people who believe it die.

B.B. When enough scientists think that When enough scientists think that it should die.it should die.

C.C. Popular Vote. Popular Vote.

D.D. When it makes predictions that When it makes predictions that don’t agree with nature.don’t agree with nature.

The End of Geocentrism The End of Geocentrism … ?… ?

Mountains and SunspotsMountains and Sunspots

Moons of JupiterMoons of Jupiter

Phases of VenusPhases of Venus

The Rise of Modern The Rise of Modern PhysicsPhysics

Isaac NewtonIsaac Newton• Three laws of Three laws of

motionmotion• Universal Universal

GravitationGravitation• The CalculusThe CalculusSimple central principals Simple central principals from which all motion, from which all motion, either on Earth or in the either on Earth or in the heavens, can be derived.heavens, can be derived.