Geocentric vs. Heliocentric A Battle for the Ages

Geocentric vs. Heliocentric

A A BattleBattle for the Ages for the Ages

Geocentric (Ptolemaic) Model

• The accepted model for 1400 years

• The earth is at the center• The Sun, stars, and

planets on their spheres revolve around the earth: explains daily movement

• To account for unusual planetary motion epicycles were introduced

• Fit the Greek model of heavenly perfection – spheres are the perfect shape, circular is the perfect motion.

Jupiter

Saturn

Mars

Venus

Earth & Moon

Mercury Sun

Ptolemy’s system provided the intellectual framework for all discussion of the universe for nearly 1600 years!! So in a very true sense, this idea was stupendously successful even though we now know that it was incorrect.

Ptolemaic System

Correction Added

•Epicycles added to epicycles

•Precision Timing for Venus & Mercury

•Earth placed “off” center.

Earth Equant

Epicycle

Deferent

The planet moves along its epicycle as the epicycle moves along the deferent around the Earth. To make the observations as accurate as possible, it was necessary to place the Earth slightly off center of the orbits, but to preserve symmetry that meant that there was an equal place (“Equant”) opposite the Earth from the center. The combined motion of the planet and the resulting retrograde motion are shown.

Off Center?!

The The RevolutionRevolution of of

IdeasIdeasThe Beginnings of the

Heliocentric Model of the Universe

Heliocentric (Copernican) System

• Sun at center (heliocentric)• Uniform, circular motion

• No epicycles (almost)• Moon orbited the earth, the earth orbited the sun

as another planet• Planets and stars still on fixed spheres, stars don’t

move• The daily motion of the stars results from the

Earth’s spin• The annual motion of the stars results from the

Earth’s orbit

Copernicus(1473-1543)

“De Revolutionibus Orbium Coelestium”

““On the On the RevolutionRevolution of the of the HeavenlyHeavenly Spheres” Spheres”

1. Earth is not the center of “everything.”

2. All the Planets revolve around the Sun!

3. Stars are very much farther away than the Sun

4. Any motion of the stars is a result of the Earth’s rotation

5. Any movement of the Sun is due to Earth’s rotation and revolution about the Sun.

6. Retrograde Motion was much easier to explain.

Earth1

Sun

1

2

3

4

5

6

6

Outer Planet

5

4

3

2

Fixed Stars

Planet's apparent path around sky.

Earth overtakes slow outer planet so the outer planet appears to slow down, move in reverse, and then move forward again with respect to the fixed stars.

Retrograde Motion

http://upload.wikimedia.org/wikipedia/commons/6/65/Retrogradeorbit.gif




Changing Ideas is Not Easy.

On March 5, 1616, Copernicus' work was banned from being taught and discussed by the Congregation of the Index "until corrected." It stayed on this list of prohibited books and teachings until 1822!!!!

Copernicus was no fool. He waited until his own death before he published his new ideas.

Change is Hard.Copernicus still used “perfect” circles for the orbits.

Copernicus ended up adding “epicycles!”

At the time his theory was a complete disaster at “predicting” the positions of the planets in the sky. Ptolemy’s model “worked” much better.

The Great The Great CompromiseCompromise

Tycho Brahe(1546-1601)

The Man with the Gold Nose

Danish Nobleman

Experimentalist & Observer. He actually made measurements

Had his own observatory built.

Made very careful measurements of star’s positions

Tycho’s Observations

Tycho’s Nova! – A “new” star appearing in the constellation Cassiopeia. Then diminished. (SN1572)

Heavens can Change!

A reason to doubt Aristotle! Maybe Ptolemy?

Tycho’s Observations

Made very precise measurements of stellar positions and planet positions in the sky

Still “measured” no stellar parallax over an entire year. Earth must be stationary.

Comet in 1577 is farther away than moon.

Tychonic ModelTycho developed a system that

combined the best of both worlds.

He kept the Earth in the center of the universe, so that he could retain Aristotelian physics and Ptolemy’s geocentric idea.

The Moon and Sun revolved about the Earth, and the shell of the fixed stars was centered on the Earth.

But Mercury, Venus, Mars, Jupiter, and Saturn revolved about the Sun.

Tychonic Model

Tycho’s Contributions

Lots of data! – Decades worth. He made the most precise observations that had yet been made by devising the best instruments available before the invention of the telescope.

Decided by measurement and observation, NOT BY DOGMA

His observations of planetary motion, particularly that of Mars, provided the crucial data for later astronomers

Tycho No More

History or Myth?

How did Tycho die?

A Model Reveals Itself

Geocentric vs. HeliocentricReaction of Contemporaries

Martin Luther (1483-1546): [Copernicus] “is a fool who wishes to reverse the entire scheme of astronomy; but sacred scripture tells us that Joshua commanded the Earth to stand still, not the Sun.”

Conservative who wanted to reform Church by returning it to a simpler, less corrupt time.Agitator for the abolishment of indulgences (payment to lessen time of deceased in purgatory).A founder of the Protestant branch of Christianity.

Response of Catholic Church to threat posed by the Reformation Movement:

At first, tolerance of dissent and liberal treatment of new ideas.Later, institution of the Counter-Reformation and the Inquisition.

Giordano Bruno (1548-1600): burned at the stake for advocating that stars are suns in their own right, and that there is a plurality of worlds like the Earth.Galileo (1564-1642):

Ah! Here is the person to decide the debate.

"Eppur Si Muove“"(And, yet it moves!")

Galileo Galilei Galileo Galilei

(1564 – 1642)(1564 – 1642)

1610 “Siderius Nuncius” (The Starry Messenger)

“Spots” on the Sun!

The Moon has mountains, craters, rocky surface with imperfections!

The “planet” Jupiter is not a pinpoint star – but a disc in the sky! WITH MOONS!

Venus has “PHASES” like the MOON

Galileo Galilei (1564 – 1642)

SUNSPOTS

“Revealing great, unusual and remarkable spectacles, opening these to the consideration of every man, and especially of philosophers and astronomers….”

The Moon Has Mountains and Valleys


Phases of Venus

Galileo observed that Venus showed phases entirely like those of the moon from full to crescent, which it must do if the Copernican theory was correct.

According to the Ptolemaic theory Venus would have to be a perpetual crescent.


Jupiter Has Moons


Galilean Moons – 4 Largest “moons” of JupiterIo, Europa, Callisto, & Ganymede

1632: "Dialogo Dei Massimi Sistemi" (In Italian! Not Latin! For the common people!) He published his masterpiece, Dialogue on the Two Dialogue on the Two Chief World SystemsChief World Systems, in which he had two people, one representing the view of Ptolemy and other the view of Copernicus, present their arguments before an intelligent layman. Galileo of course gave the Copernican the brilliant best of the battle.


The Pope was persuaded that Simplico, the character who upheld the views of Ptolemy in the book, was a deliberate and insulting caricature of himself. The book was all the more damaging to those who felt themselves insulted, because it was written in vigorous Italian for the general public (and not merely for the Latin-learned scholars) and was quickly translated into other languages -- including Chinese!

Scientific Martyr

Teaches Heliocentric IdeasClaims “proof” for Earth’s motion.Trial by Church (threatened with instruments of torture), forced to recant views (1633).Confined to house arrest. Formulates “new science” of mechanics.Loses his sight (blinded) by Sun observationsMost influential combination of experimentalist and theorist world has ever seen.Often credited rightly with having started modern science.


"...a sickly child, with thin limbs and a large, pasty face surrounded by dark curly hair. He was born with defective eyesight-myopia plus anocular polyopy (multiple vision). His stomach and gall bladder gave constant trouble; he suffered from boils, rashes, and possibly from piles, for he tells us that he could never sit still for any length of time..."

Still, there are problems to solve….

Math skills - Kelper's skills were extraordinary. He could not reconcile Tycho's very careful observations with the Models of Ptolemy, Copernicus, nor Tycho!!!

Advancing science, more than ethics, Kepler simply stole the observations upon the sudden and ironic death of Tycho

Johannes Kepler’s Work

His incredible effort took 29 years!! He waged a "war" on understanding the orbit of Mars.

Heliocentric Model fits the observations best from a simple view point (Copernician) But *not* circular orbits.

An Idea! Orbits are not Circles!

Ellipses

Kepler’s Three Empirical Laws of Planetary Motion

1. The orbital paths of the planets are elliptical, with the Sun at one focus


2. An imaginary line connecting the Sun to any planet sweeps out equal areas in equal time..

Area 2

Area 1


3. The square of a planet’s orbital period is proportional to the cube of its semi-major axis.

P2 (years) = A3 (astronomical units)

1 Astronomical Unit = The Earth-Sun Distance (98 million miles)

Kepler’s Third Law

Object a (AU) P (year) a**3 P**2

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 3.53

Jupiter 5.20 11.9 141. 142.

Saturn 9.54 29.5 868. 870.

Uranus 19.2 84.0 7,080. 7,060.

Neptune 30.1 165. 27,300. 27,200.

Pluto 39.5 248. 61,600. 61,500.

But!!…..

Kepler did not know WHY

planet’s move as they do.

Isaac Newton (1642-1727)

Born in England on Christmas day.

Bubonic Plague 1665?

While home for 2 years with nothing to do he made his most profound discoveries and proposed his most startling theories.

Time Marches On

In 1684 – was in a discussion with Edmund Halley, when Halley remarked “But why do planet’s move the way they do?”

Newton astounded everyone with the answers ( from his work 20 years earlier!).

“Philosophiae Naturalis Principia Mathematica”

Newton’s Three Laws of Motion

The laws explained not only why planets move as they do, but why objects in general move as they do.

Newton’s First Law

Objects at rest stay at rest unless a “net force” is applied.

• Note: Newton’s First Law Does NOT say…

• This law does not say that every moving object has a “force” acting on it!

• This law does not say an object at rest has “no force(s)” acting on it!

Objects in uniform straight line motion stay in straight line motion unless a “net force” is applied.

Newton’s Second LawThe acceleration 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/mOR

Fnet = ma

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.

“To every action there is an equal and opposite re-action.”

Law of Universal Gravitation

Matter attracts matter

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MGMF

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Geocentric vs. Heliocentric A Battle for the Ages