© 2005 Pearson Education Inc., publishing as Addison-Wesley The Planets Prof. Geoff Marcy The Nature of Scientific Theories Giants of Scientific Thinking

© 2005 Pearson Education Inc., publishing as Addison-Wesley

The PlanetsProf. Geoff Marcy

• The Nature of Scientific Theories• Giants of Scientific Thinking• Astrology

Lecture 4b2012 Sept. 6


Announcements• Read Chapter 4 !

• Homework: MasteringAstronomy: Chapt 4.

Past Homework Assignments:- Assignment Chapters 1&2: Due tomorrow 6pm- Assignment Chapters 3: Due tomorrow 6pm- Question: Raise your hand if you can’t get into MasteringAstronomy.

-Observation Project: Due Right now!

Tue, Wed, Thu 12-1: Disc. Sections Not full!

To purchase stand-alone access to MasteringAstronomy if you didn’t buy a book or access code in the bookstore.

You can buy both the eBook and MasteringAstronomy: $85.


Scientific Thinking

• It is a natural part of human curiosity: Search for understanding and truths that explain many facts.• We draw conclusions based on our experiences.• Progress is made through “trial and error.”

Hypothesize. Then test your hypothesis.

Eating pasta makes me get fat . . .


Nicolaus Copernicus (1473-1543)

He thought Polemy’s model was contrived

Yet he believed in circular motion

De Revolutionibus Orbium Coelestium


Copernicus’ Heliocentric Model

• Sun is at center• Earth orbits like any other planet• Inferior planet orbits are smaller• Retrograde motion occurs when we “lap”

Mars & the other superior planets


Johannes Kepler (1571-1630)

• Greatest theorist of his day

• Imagined planets on “heavenly spheres”


Kepler’s Laws

1. Each planet’s orbit around the Sun is an ellipse, with the Sun at one focus.


Eccentricity of an Ellipse


Kepler’s 2nd LawA planet moves along its orbit with a speed that

changes in such a way that a line from the planet to the Sun sweeps out equal areas in equal intervals of time.


Kepler’s 3rd Law The cube of a planet’s average distance from the

Sun is equal to the square of its orbital period.

(Use units of years and AUs.)

a3 = P2


Galileo Galilei (1564-1642)• First man to point a

telescope at the sky• wanted to connect physics

on earth with the heavens• Dialogue Concerning the

Two Chief World Systems [written in Italian]

This book got him in trouble with the Church!


Galileo’s Observations• Galileo discovered

that Jupiter had four moons of its own.

• Jupiter was the center of its own system.

• Heavenly bodies existed which did not orbit the earth.

Tycho Brahe (1546-1601)

• Greatest observer of his day• Born into the most prestigious

families in Denmark• King Fredrick II offered him the

entire island of Hveen for observations

• Best charts of planets positions• Johannes Kepler

• Kepler’s task: explain Mars’s orbit

Tycho Brahe(1546-1601)




• Best charts of planets positions• Two observers: Johannes

Kepler & Frank Tengnagel• Kepler’s task: explain Mars’s

orbit

Tycho Brahe (1546-1601)




• Best charts of planets positions• Two observers: Johannes Kepler & Frank Tengnagel• Kepler’s task: explain Mars’s orbit

Tycho Brahe(1546-1601)

Exhumed in 2010


Kepler’s 1st Laws

Each planet’s orbit around the Sun is an

ellipse, with the Sun at one focus.

Kepler could not match Brahe’s precise measurement of Mars’ orbit.A tiny different of 8 arc minutes (0.13o) remained.Then he abandoned the idea of “uniform” and “circular” motion.

Kepler’s 2nd LawA planet moves along its orbit with a speed that changes in such a way that a line from the planet to the Sun sweeps out equal areas in equal intervals of time. (Now called: conservation of angular momentum.)

Kepler’s 3rd Law The cube of a planet’s average distance from the Sun is equal to the square of its orbital period.

Orbital period: P (measure in years)planet’s average distance: a (measure in AU)

P2 = a3

aMore precisely: a is the semi major axis

Question:An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun?

A. 4 years

B. 8 years

C. 16 years

D. 64 years

Hint: Remember that P2 ~ a3


Question:An asteroid orbits the Sun at an average distance a = 4 AU. How long does it take to orbit the Sun?

A. 4 years

B. 8 years

C. 16 years

D. 64 years

We need to find P so that P2 = a3.Since a = 4, a3 = 43 = 64Therefore P= 8, P2 = 82 = 64

Calculate the orbital period of:

Planet a (AU) Period (yrs)Mercury 0.4 92 days = 0.25 yrVenus 0.7 214 days = 0.59 yrsEarth 1.0 1.0Mars 1.5 1.8Jupiter 5.0 11.2Saturn 10 32Uranus 20 89Neptune 30 164Pluto 50 354

WHY do planets move on elliptical orbits?

Astronomers Kepler, Halley, Wren, and Hooke proposed an inverse square law of gravity:

Force of gravity ~ 1 / distance2

In 1684, Sir Christopher Wren issued a small prize (40 shillings) for the first person who could prove that Kepler’s first law follows from an the gravity law above.

In August of 1684, Halley met Isaac Newton in Cambridge…

• Realized the same physical laws that operate on Earth also operate in the heavensÞ one universe

• Discovered laws of motion and gravity

• Much more: experiments with light; first reflecting telescope (using mirrors rather than lenses)

• Invented calculus in parallel to Friedrich Leibnitz in Germany

How did Newton change our view of the Universe?

Sir Isaac Newton (1642-1727)

1. What determines the strength of gravity? The Universal Law of Gravitation1. Every mass attracts every other mass.2. Attraction is directly proportional to the product of their

masses.3. Attraction is inversely proportional to the square of the

distance between their centers..

Question:Is the force the Earth exerts on you larger, smaller, or the same as the force you exert on it?

A. Earth exerts a larger force on you.

B. I exert a larger force on Earth.

C. Earth and I exert equal and opposite forces on each other.

Question:Is the force the Earth exerts on you larger, smaller, or the same as the force you exert on it?

A. Earth exerts a larger force on you.

B. I exert a larger force on Earth.

C. Earth and I exert equal and opposite forces on each other.


Galileo’s observation of the phases of Venus was the

final evidence which buried the geocentric model. Geocentric Heliocentric

No gibbous or full phases! All phases are seen!

Galileo observed all phases!


The Scientific Method1 Question2 Hypothesis

– a tentative explanation3 Prediction4 Test5 Result

– confirm, reject, or modify

should be the same no matter who conducts the test


• Science seeks explanations for observed phenomena that rely on natural causes.

• Science progresses through the construction and testing of models of nature that explain the observations as simply as possible.! Occam’s Razor

• A scientific model must make testable predictions that could force us to revise or abandon the model.

Hallmarks of Good Science

-- a concept or set of ideas (a “model”) that survives repeated testing

Theory


Bad Scientific Practice

• pseudoscience – beliefs that masquerade as science, but do not change as new evidence comes in that contradicts those beliefs.

• nonscience – establishes “truths” through belief and faith. Tests are not done.


Astrology

• Claims the positions of the Sun, Moon, & planets determines each person’s personality and each person’s future.


Astrology

Theory:

The positions of the planets, sun, and moon

at the time of your birth determine your

personality and your future every day.



Signs of the Zodiac

AQUARIUS January 19-February 17 PISCES February 18-March 19

ARIES March 20-April 18 TAURUS April 19-May 19

GEMINI May 20-June 19 CANCER June 20-July 21 LEO July 22-August 21 VIRGO August 22-September 21

LIBRA September 22-October 22

SCORPIO October 23-November 20 SAGITTARIUS November 21-December 20

CAPRICORN December 21-January 18

http://www.sfgate.com/eguide/horoscope/






Horoscope Sept. 6, 2012

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Test of Astrology

• Write your “sign” of the zodiac

on one sheet of paper.

• Choose the horoscope that

best describes your day today

• Write the NUMBER of that

paragraph 1 - 12 on that paper.

Signs of the Zodiac

AQUARIUS January 19-February 17 PISCES February 18-March 19

ARIES March 20-April 18 TAURUS April 19-May 19

GEMINI May 20-June 19 CANCER June 20-July 21 LEO July 22-August 21 VIRGO August 22-September 21

LIBRA September 22-October 22

SCORPIO October 23-November 20 SAGITTARIUS November 21-December 20

CAPRICORN December 21-January 18








123456789101112


Existing Astrology Theory:

You can predict your future.

If Theory is True:

You will recognize your horoscope: It pertains to you!

If Theory is not true.

You will choose a random horoscope.


123456789101112


123456789101112

Chose #1? Stand up !


Existing Theory: Astrology works

The horoscope for your sign of the zodiac

allows you to predict your future.

If Theory is True:

People will recognize their horoscope.

If Theory is not true.

People will not recognize their horoscope.


Astrology:What is the Mechanism

that makes it work?

What force makes the planets determine your entire life?

What is the “energy” that makes planets control your life?

What force exerted by planets acts on you at the moment of birth to determine the rest of your life?


Astrology:Invent your own

Why do only planets and moons affect your life?

Other objects exert great gravitational forces on you, such asnearby buildings, aircraft, mountains.

Quiz: Invent your own “astrology” based on the positions of some other objects around you.

Documents

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Planets Prof. Geoff Marcy The Nature of Scientific Theories Giants of Scientific Thinking