The Copernican Revolution

The Copernican Revolution.

Nicolaus Copernicus (1473-1543).

Born in Thorn, Prussia on the Vistula (now Torun, Poland) on Feb. 19, 1473 as Mikolaj Kopernik (Niklas Koppernigk).

The youngest of four children.

Father was a prosperous merchant.

Father died in 1484, and the children were adopted by their maternal uncle, Lucas Watzelrode, a priest with some scholarly attainments who became Bishop of Ermland in 1489.

It was decided that Copernicus should be trained for the church.


Studied mathematics and science at the University of Cracow (1491-1494).

There, he acquired an attraction for the new humanistic studies.

He left without taking his examinations for his degree.

Studied canon law at the University of Bologna.

Upon returning to Poland, named Canon of Frauenburg – the northernmost Catholic diocese in Poland – at age of 24.

Same year (1497), returned to Italy to enter the medical school at Padua.

Took time to lecture at Rome on astronomy and accept a doctorate in canon law at Ferrara.

Returned to Poland in 1505 (age 32) for good not only a humanist trained in Greek, mathematics, and astronomy, but also a jurist and physician.


Religious duties.

He was his uncle’s private secretary and physician.

He ministered to the sick and indigent.

He held various political offices.

Best known during his lifetime for a coinage-reform system he proposed to the Diet in 1522 (age 49).

Devoted an enormous amount of time to his hobby astronomy, but was not an experimenter.

Considered an authority on the subject by the time he had reached middle age.

Completed De Revolutionibus Orbium Coelestium (On the Revolutions of the Heavenly Bodies) in 1530 (age 57), which was not published until immediately before his death in 1543 (age 70).

Copernicus’ Heliocentric Theory.

His astronomical background.

Just a hobby.

Scientific knowledge well known – consulted by the papacy on possible calendar reform.

His observations were not very numerous nor accurate.

It is said that he never actually observed Mercury.

He analyzed the results of others .

De Revolutionibus Orbium Coelestium (On the Revolutions of Celestial Spheres)

A student of wide learning, knew of Greek schemes where the earth was not centrally located.

In chapter 3 of his book, he cites the Pythagoreans as an authority.

Carl Sagan, in Cosmos, speculates that Aristarchus, whose recently discovered works were the source of great excitement in Italian universities when Copernicus went to medical school there, provided inspiration.

In his manuscript, mentions Aristarchus’ priority.

In letter to Pope Paul III:

According to Cicero, Nicetas had thought the earth was moved… According to Plutarch [who discusses Aristarchus]… certain others had held the same opinion. When from this, therefore, I had conceived its possibility, I myself also began to mediate upon the mobility of the Earth.

In light of these alternatives, he decided to take a fresh look at contemporary cosmology, which he found unsatisfactory.

He was taught that the earth was stationary at the center of the universe.

Ptolemaic cosmology, with its myriad of circles, had to account for retrograde motion by displacing the center of the orbit sphere from the universe.

Hence, though “saving the appearances” for the most part, the theory was inconsistent.

Believed the discrepancy could be overcome if the sun was located at the center of the earth.

Earliest evidence of Copernicus’ idea of heliocentric theory can be found in 1514 when he wrote Commentariolus (“Brief Treatise”), where he:

He complains that the equant system of Ptolemy was “neither sufficiently perfect nor pleasing to the mind.”

Listed seven assumptions, of which two are most significant:

3. All the spheres surround the Sun as though it were in the middle of all of them, and therefore the Sun is near the middle of the universe, and;

7. What appears as the direct and retrograde movements arises not from the planets themselves, but from the Earth. This motion alone therefore suffices to explain many apparent irregularities in the heavens.

He worked out in detail a heliocentric theory to explain the thousands of observations.

Based on circular motions of the planets, of which Copernicus was an advocate; thus, he was still bound by traditional prejudices.

“The mind shudders” at the alternative, because “it would be unworthy to suppose such a thing in a creation constituted in the best possible way.”

He made an exorbitant amount of calculations over many years to show that a heliocentric theory was superior to the Ptolemaic approach.

The Actual Theory.

Main Assumptions (The Relativity of Motion):

The earth and the planets revolve around the sun.

Inferior Planet – Closer to the sun than the earth.

Superior Planet – Farther from the sun than the earth.

The earth spins on a north-south axis from west to east at a rate of one rotation a day.

Old theory – if the earth moves, such motion would tear it apart.

Copernicus’ answer – the even faster motion induced by the celestial sphere required by the alternative hypothesis would be even more devastating.

Conjunction and Opposition.

Conjunction – the planet and the sun occupy the same spot in the sky.

For superior planet, only once, when the sun is on a straight line between the earth and the planet.

For inferior planet, twice:

Inferior Conjunction – planet between earth and sun; and

Superior Conjunction – sun between earth and planet.

Opposition – For superior planets only, when the earth is between the planet and the sun, the planet occupies the spot in space exactly opposite where the sun is.

The above led Copernicus to correctly order the solar system and approximate the scale of the solar system.

Sidereal and Synodic Periods of the Planets.

Sidereal Period – Actual period of revolution about the sun with respect to fixed stars.

Synodic Period – Apparent period of revolution about the sky with respect to the sun, (e.g., the time it takes a planet to go from opposition to opposition).

Relative distances of the planets.

From the above, Copernicus was able to determine the distances of the planets from the sun, based on astronomical units (the distance between the earth and the sun).

Table 1. Planetary Distances.


FIGURE                  FIGURE

Mercury                 0.38                          0.387

Venus                     0.72                          0.723

Earth                     1.00                           1.00

Mars                      1.52                           1.52

Jupiter                   5.22                          5.20

Saturn                   9.17                          9.54

Although he rejected most of Ptolemy as unworthy of the perfection of heavenly bodies, Copernicus introduced a series of eccentrics and epicycles to take care of irregularities.

Finally, Copernicus did NOT prove that the earth revolves around the sun, he merely proposed, and sincerely believed, that it did.

Publication of De Revolutionibus Orbium Coelestium.

Shortly after completion a summary was circulated.

He was reluctant to publish anything in detail for fear that his revolutionary idea might meet with ridicule.

Given the current dissension between the Catholics and the Protestants, he feared his work might aggravate the situation and prove scandalous in its assertion that the earth is not at the center of the universe in that it might be construed as contradicting one possible literal interpretation of the bible.

The possibility of man’s loss of dignity was not considered as, while a the top of the animal spectrum, man was considered at the bottom of the intellegent creatures, having been corrupted by original sin.

More likely reasons it was not published:

Far from the major international centers of printing that could handle a book as large and as technical as De Revolutionibus.

Copernicus was aware that his manuscript was full of numerical inconsistencies, and he knew that he did not take full advantages of the opportunities afforded him by the heliocentric theory.

This is apparent in Book VI, where he discusses planetary latitudes, inheriting much of the worst of the Almagest.

Furthermore, Copernicus was far from the intellectual centers where he could discuss and refine his ideas with technically competent colleagues.

Visited in 1539 by the German mathematician Rheticus (Georg Joachim von Lauchen, 1514-1576), who stayed for two years and persuaded Copernicus to allow him to publish a small treatise on the theory and then to prepare a full text.

Published in Nuremburg in 1543.

An advanced copy reached Copernicus on May 24, 1543. Later that same day, he died.

From the title page of the first edition, (equivalent to the modern publisher’s dust jacket blurb):

You have in this newly created and published book, diligent reader, the motions of the fixed stars and planets restored from both the old and new observations, and furthermore, furnished with new and wonderful hypotheses. You also have the most convenient tables from which you can with greatest ease calculate their positions for any time. Therefore buy, read, and profit!

Note the emphasis on predicting celestial positions.

Ptolemy would have claimed “for the first time”, rather than “at any time.”

First edition saw fewer than 500 copies printed and distributed mainly in the Lutheran sphere.

A second edition was published in Basil in 1566 and was widely distributed in England and the Catholic countries, so that by 1600, it was readily available.

Controversy of De Revolutionibus Orbium Coelestium.

The initial publication was marred by an unsigned (and unauthorized) preface by the German theologian Andreas Osiander (1498-1552).

Osiander was probably responsible for the work’s rather protracted title.

Osiander described the theory as no more than a “mathematical convenience.”

“These hypotheses need not be true nor even probable as long as they provide a calculus that fits the observations…. Let no one expect truth from astronomy, lest he be a bigger fool than when he entered.”

On the other hand, this preface spared the book the theological criticism it might have otherwise attracted.

The text was rarely taught openly, and then almost always as merely a hypothesis with not much stock taken in the heliocentric viewpoint.

Catholic Church, in 1616, placed work on list of forbidden books “until corrected” by local ecclesiastical censors.

It remained there until 1835.

Owen Gingerich found that only 60% of the sixteenth century copies in Italy were censored while none were “corrected” in Iberia. (Carl Sagan, Cosmos).

Martin Luther described Copernicus as:

“an upstart astrologer… This fool wishes to reverse the entire science of astronomy. But Sacred Scripture tells us that Joshua commanded the Sun to stand still, and not the Earth.”

Giordano Bruno, an ecclesiastical reformer and philosopher, praised Copernicus’ cosmology and was burned at the stake for it in 1600.

Although, Bruno may have been punished for other reasons.

Even some of his advocates claimed the main attraction to Copernicus’ theory was it conveniently accounted for planetary motion and they did not really believe in a Sun-centered universe.

Ramifications of Copernicus:

Copernicus – Ramifications of his ideas.

Did NOT improve that significantly upon Ptolemy’s predictions, (certainly not enough to get excited about).

Copernicus died believing in the truth of his theory, but he did not have any convincing proof that he was correct.

His calling the idea a “hypothesis” did not take away from his convictions as he interchanged the words “hypothesis” and “principle” frequently.

Demoted the status of the earth to an ordinary planet.

Revolutionized science.

Eventually led to new laws in physics.

Made the universe vastly bigger than previously imagined.

Profoundly altered Man’s perception of himself and his relationship to the universe.

Freud: “The first great outrage of science against man.”

First to describe the precession of the equinoxes, (but not to explain the mechanism behind it).

Because of his insistence that circular motion was the only possible type, his system was also imperfect.

It was perfected by Tycho Brahe and Johannes Kepler.

Indeed, Copernicus maintained that the entire universe was spherical.

Tycho Brahe (1546-1601).

Tycho’s Background.

Born at Knudstrup in Skane, south Sweden, then the province of Denmark to a noble family and had an advantages upbringing.

Sent by his uncle to study law at the University of Leipzig in 1562, Tycho was so impressed by the solar eclipse in 1560 that, while his tutor slept, he turned to studying the sky.

Tycho’s discovered errors in the Alfonsine and Prutenic tables.

He had no instruments other than a globe and a pair of compasses.

He was quite dismayed by the seriousness of the errors in these tables of planetary motions.

Vowed to build observing instruments which would enable him to record the most accurate observational records possible.

He became the greatest pre-telescope observer, his discoveries bringing him wealth and fame.

Tycho’s Astronomy.

1572 supernova in Casseopia.

Discovered by and named for Tycho.

Proceeded to prove that the supernova lay well outside the realm of the Earth’s atmosphere.

The moon has a very slight, but perceptible, parallax.

The supernova did not.

This questioned the viability of Aristotle’s physics.

He Published in the book De Nova Stella (The New Star).

In 1577, he proved that a newly discovered comet travelled between the planets.

This confirmed his reputation.

Refuted the notion that planets orbited the Earth in solid crystalline spheres (which the comet would have shattered).

Tycho, not able to come to grips with the Copernican Theory, devised his own which said that the all the planets (and comets) orbited the Sun, which in turn orbited the stationary Earth.

He could not reconcile Copernicus’ theory with certain biblical passages.

He could not imagine anything as heavy and “sluggish” as the earth to be in motion.

Though looking for it, could not find any stellar parallax, which meant:

The Stars were both exceedingly far and large; or

The earth was stationary.

In 1576, Frederick II, the King of Denmark gave Tycho the island of Hven.

Offered to defray the cost of erection and the necessary astronomical instruments.

Provided a suitable salary.

Castle – Uraniborg (The Center of the Universe).

Included a library, laboratory, living quarters, workshops, a printing press, and even a jail.

Observatory – Stjerneborg.

Became the astronomical center of the world.

Tycho ruled Hven like a king.

Many significant observations were made here, many of which influenced astronomical constants and were quite relevant in the reformation of the calendar.

In 1588, Frederick II died.

His successor, Christian IV, was not prepared to tolerate the arrogant and argumentative Tycho.

Tycho left Hven after 20 years.

Tycho settled in Prague at the invitation of Emperor Rudolf II, who made him imperial mathematician.

He Began to analyze the lunar and planetary observations he had collected at Hven.

He intended to build another Uraniborg, but died before its completion.

Having been impressed by the Mysterium Cosmographicum, Tycho asked and was joined by the young Kepler, who was also in exile from his native land, in 1600.

A year later, Tycho died, leaving his observations to Kepler in hopes that he might be able to verify the Tychonic theory of planetary motion.

Ironically, Tycho’s extensive and remarkable collection of observations was used by Kepler to establish the Copernican view.

Had it not been for the unwavering precision of Tycho’s observations, Kepler might have searched in vain for what eventually came to be known as his laws.

Johannes Kepler (1571-1630).

His Youth.

Conceived on the 16th of May, 1571 at 4:37am.

Born in Weil-der-stat, Wurttemberg (southwestern Germany), on Dec 27, 1571.

Born of a noble, but poverty stricken family.

His father was a soldier of fortune until he acquired a tavern in 1577.

A sickly child, Kepler attended a German elementary school at Leonberg when not working in the tavern.

Domestic bankrupcy after three years led to his being withdrawn and sent to the labor fields.


Studied theology and the classics at the University of Tubingen.

Became acquainted with the teachings of Copernicus.


Destined for a career as a Lutheran minister.

Held chair of astronomy and mathematics at University of Graz from 1594 to 1600 (ages 23 – 29).

From then on, he pursued the subject of astronomy for the rest of his life.

Eventually, the power of the Catholic Church grew at Graz to such an extent that Kepler, a protestant, was forced to quit his post.

Became assistant to Tycho Brahe at Brahe’s observatory in Prague in 1601 (age 30).

At Brahe’s death in 1601, assumed the position of imperial mathematician and court astronomer to Emperor Rudolph II.

Became mathematician to the states of Upper Austria in 1612 (age 41).

In 1626 (age 55), moved to Ulm, where he completed and published the Rudolphine Tables, astronomical tables started by Brahe.

These tables were a must for 17th century astronomers.

His Astronomical Studies.

Unlike Copernicus, his primary occupation was the study of astronomy.

In his official capacities, he edited astrological almanacs.

His serious occupation was the study of mathematics and planetary motion.

His attraction to the Copernican system:

Mathematical simplicity.

Kepler regarded the sun, in both the mystic and the natural sense, as the center of the universe.

Kepler was also convinced that God had created the universe to conform to simple mathematical procedures.

This belief led directly to the three laws of planetary motion collectively known as Kepler’s Laws.

He also discovered relationships between the orbital speeds of planets and the notes in a musical scale; hence, creating a scheme of divine musical harmony which was published as Harmonices Mundi (Harmonies of the World) in 1619.

Made contributions to other fields:

Studied and wrote on the subject of optics, including publishing a design for a telescope after using one of Galileo’s. His design was to become more widely adopted.

Mathematics – developed a system of infinitesimals which was the forerunner of calculus.

Most notable writings.

Mysterium Cosmographicum in 1596.

Astronomia Nova de Motibus Stellae Martis ex Observationibus Tychonis Brahe in 1609.

Harmonice Mundi (Harmonies of the World) in 1619.

Epitomes Astronomiae Copernicanae (Epitome of Copernican Astronomy) from 1618-1621.

The Road to Theory.

Accepting the model of Copernicus, Kepler tried to see if a series of regular geometric solids (circles) could be configured in such a way as to accurate predict planetary motions and conform to the Copernican heliocentric idea. It was published under the title of Mysterium Cosmographicum (The Cosmographic Mystery) in 1596.

The above brought Kepler in contact with Tycho Brahe, who brought the former into this observatory as an assistant.

Upon Tycho’s death, Kepler inherited his extensive observations.

Tycho had suggested to concentrate on the observations of Mars.

After three years of going over the data and the calculations, Kepler was convinced he had come upon the correct formula for the martian circular orbit.

Two of Tycho’s further observations, far too discrepant for Kepler’s formula, caused Kepler to write:

“Divine Providence granted us such a diligent observer in Tycho Brahe that his observations convicted this… calculation of an error of eight minutes; it is only right that we should accept God’s gift with a graceful mind… If I had believed that we should ignore these eight minutes, I would have patched up my hypothesis accordingly. But, since it was not possible to ignore, those eight minutes pointed the road to a complete reformation of astronomy.”

From analyzing Tycho’s observations of Mars’ orbit, Kepler concluded that Mars had an elliptical orbit at varying speeds depending upon its distance from the sun.

Incorrect mathematics caused Kepler to at first reject the correct hypothesis.

“The truth of nature, which I rejected and chased away, returned by stealth through the back door, disguising itself to be accepted….Ah, what a foolish bird I have been!”

This idea was extended by analogy and subsequently observational evidence to the other planets.

Published in his book of 1609 Astronomia Nova (The New Astronomy), this theory empirically abolished the ancient notion that planetary motions were circular.

The physical theory which accounted for the elliptical orbits was published in his Epitome Astronomiae Copernicanae between 1618 and 1621.

Contained observational evidence supporting ellipsoid orbit for the remainder of the planets.

Kepler’s Laws.

Summerized and systemized the vast amount of empirical data on planetary motion amassed by the astronomers of his time.

Served as the foundation for the principles subsequently set forth by Sir Isaac Newton.

Kepler’s Laws are but a specific case of Newton’s theory.

The Laws.

1. Planets travel in elliptical paths around the sun, the sun being at on of the foci.

2. The areas described in a planetary orbit by the straight line joining the center of the planet and the center of the sun are equal for equal time intervals (i.e., the closer a planet comes to the sun, the more rapidly it moves).

3. The squares of the times required for different planets to describe a complete orbit are proportional to the cubes of their mean distances form the sun.

P2 = Ka3,

P represents the siderial period of the planet, a is the semimajor axis of its orbit, and K is the numerical constant which depends on the kinds of units chosen to measure time and distance. When astronomical units are used, the formula becomes:

P2 = a3

Kepler’s Proofs and Overall Ramifications.

Observed and wrote about the nova of 1606.

Evidence of how mistaken we were about the changelessness of the universe.

Empirical evidence and provable hypotheses led to the gradual acceptance of a modified Copernican theory and greatly changed the methods of science.

Kepler provided the “brawn” behind the Copernican revolution.

He had to defend the Copernican viewpoint not only against Ptolemy, but against Tycho.

The philosophical implications of a moving Earth.

“It was not fitting that man, who was going to be a dweller in this world and its contemplator, should reside in one place as in a closed cubicle… It was his office to move around in this very spacious edifice by means of the transportation of the Earth his home.”

In addition, the astronomer “needed to have the Earth a ship in its annual voyage around the sun.”

Tries to head off further objection by qualifying, when he intimates that the earth is only part of a part, “But I am speaking now of the Earth in so far as it is a part of the edifice of the world, and not of the dignity of the governing creatures which inhabit it.”

Against Aristotle’s emphasis on strict observation.

“Our uncultivated eyesight…”

He does not defend the truth of the Copernican view merely on the merits of its accuracy or on its mathematical simplicity as Copernicus did.

Indeed, he points out that these arguments work as much in favor of Copernicus as they do Tycho.

Copernicus was defended on the basis of its correctness in defining the physical mechanism; thus taking aim not at Ptolemy, but against Aristotlean physics.

From the opening of the Epitome: “Astronomy is a part of physics.”

From the forth book: Astronomy has not one, but “two ends: to save the appearances and to contemplate the true form of the edifice of the world.”

Even given the inordinate evidence, Harvard and Yale taught Ptolemiac theory as a viable cosmological alternative during their early years.

Copernican Theory was not 100% accepted until the mid 1800’s when Bessel discovered the parallax of Cygnus 61.

Galileo Galilei (1564-1642).

His Youth.

Born in Pisa on February 15, 1564.

His father, who belonged to a noble, but impoverished Florentine family, was a cloth merchant highly reputed for his skills in mathematics and music.

At the age of twelve or thirteen, studied Greek, Latin, and logic at the monastery of Vallombrosa, near Florence.

A novice for a short time, his father withdrew him from the charge of the monks.


His father sent him to study medicine in 1581 (age 17) at the University of Pisa.

Mainly out of fear that should Galileo become interested in music or mathematics, might suffer a economic fate similar to his.

The young Galileo was already proficient in music.

He incurred the wrath of his professors by refusing to accept on faith dogmatic statements based solely on the authority of the great writers of the past.

His classmates nicknamed him “Wrangler”.

In 1585 (age 21), he turned to mathematics and science.

Lacking the money, he was forced to withdraw and returned to Florence the same year.



Before studying mathematics, Galileo was fascinated by the swinging of a church chandelier.

Timed swings with his pulse.

Led to the discovery of the isochronism of a pendulum, i.e., the fundamental law that the time taken for the oscillation of a pendulum is the same regardless of the amplitude of the swing.

Suggested applying this principle to clocks.

Although he never built a clock, he son unsuccessfully attempted to build a pendulum clock based on his father’s notes.

In 1587 and 1588, he delivered two papers before the Florentine academy on the site and dimensions of Dante’s Inferno.

Center of gravity.

In Florence, he invented the hydrostatic balance for measuring the center of gravity of solids.

In 1588 (age 24), wrote a treatise on the center of gravity in solids.

He was called “the Archimedes of his time.”

As a result, he was awarded the post of mathematical lecturer at the University of Pisa in 1589, which he took after briefly considering earning his living in the East.

Falling bodies.

During the next two years, from 1588 to 1591, he performed a series of experiments which demonstrated that bodies of differing weights fall at the same velocity.

Legend has it that these experiments were performed at the top of the leaning tower of Pisa, but this fact is doubtful.

He showed that the path of a projectile was in a parabola.


The law of inertia (Newton’s First Law).

“A body at rest tends to remain at rest and a body in motion tends to remain in motions, unless acted upon by an outside force.”

Disproved rest is the “natural state of matter.”

Objects move further when friction is reduced.

Acceleration is constant.

A ball rolling down an inclined plane.

Aristotle – the ancient nemisis.

Galileo’s discoveries were in complete contradiction with the prevailing theories of Aristotle’s contemporaries.

To make matters worse, Galileo caused further ire from the authorities by a burlesque ridiculing university regulations.

The enmity of his colleagues aroused, Galileo resigned his post at Pisa.

In 1592 (age 28), he was appointed professor of mathematics at Padua, where he remained until 1610.

Designed and made a calculating device known as a “military and geometric compass”.

Wrote a short treatise on mechanics.

Established a European reputation as a scientist and inventor.

His lectures, which were attended by the most distinguished individuals throughout Europe, were so popular they were held in a hall that held two thousand people.

The weight of the atmosphere.

“Nature abhors a vacuum.”

Correctly surmounted the atmosphere had weight.

Failed to measure the weight.

Idea picked up by his student Evangelista Torricelli, who supplied the correct solutions.

Died after being seized with fever while teaching his pupils Viviani and Torricelli on January 8, 1642 and was buried in the chapel of Santa Croce in Florence.

His Astronomical Studies.

The Telescope.

He learned in 1609 of the 1608 invention of the “spyglass” by the Dutch lens maker Hans Lippershey.

He soon built and improved upon the design.

He was probably the first to use the telescope for astronomical purposes.


The Moons of Jupiter.

A miniature solar system.

It had been argued that if the earth were in motion, the moon would not be able to keep up with it; hence, could not revolve about the earth.

The phases of Venus.

The moon shines reflected light.

Mountainous configuration of the moon – therefore, no longer a perfect sphere.

Ludovico delle Colombe – an outspoken critic – claimed the mountains and valleys were encapsulated with a crystalline material whose outer surface was completely smooth, thus maintaining the perfectness of the sphere.

Galileo agreed the presence of the crystalline material was a splendid suggestion and added that there mountains of this same invisible substance which rose 10 times higher than the mountains that could be seen on the moon!

The rings of Saturn.

– Totally baffled by them – thought they were symetrically attached, resembling ears.

– Dutch astronomer Christiaan Huygens discovered their true nature in 1659.

The existence of sunspots.

– Again, an imperfect sphere.

– Blemishes were rationalized by critics to be satellites revolving around the sun.

– Galileo noted their movement as an indication that the sun rotated.

The Milky Way contains thousands of stars.

Published Siderius Nuncius (The Starry Messenger) in 1610.

Investigations were rewarded with the appointment as professor at the University of Florence and as philosopher and mathematician extraordinary to the Grand Duke of Tuscany in 1610 (age 46).

He had previously named the Jovian moons the “Medicean Stars” in honor of the Grand Duke Cosimo de Medici.

A large salary and unlimited research time.

On the truly remarkable effect the telescope had on the study of astronomy, Pascal says,

“The weakness of their [the ancients] eyes not yet having been artificially helped, they attributed this color [the Milky Way] to the great solidity of this part of the sky…” It would be inexcusable for us “to retain the same thought now that, aided by the advantages of the telescope, we have discovered in the Milky Way an infinity of small stars whose more abundant splendor has made us recognize the real cause of this whiteness.”

Galileo and the Copernican theory.

Long accepted the Copernican model.

He wrote to Kepler in 1597 that he had “become a convert to the opinions of Copernicus many years ago.”

He continued to teach the Ptolemiac system at Padua.

Recent studies suggest his convictions wavered.

He believed in circular motion.

He went public when his discoveries gave him concrete and visible confirmation –

“all my life and being henceforth depends” on the establishment of the new theory.

He traveled to Rome in 1611 to demonstrate his findings to the ecclesiastical authorities.

Letters on the Solar Spots (1613).

Admonished by Pope Paul V to relinquish his heretical position.

Galileo’s defense: “Nature…is inexorable and immutable; she never transgresses the laws imposed upon her.”

Summoned before Cardinal Bellarmine and warned not to hold or defend the Copernican theory.

Galileo said he would obey.

Primary reason the Roman Catholic Church in 1616 issued a prohibition decree which stated that the Copernican doctrine was “false and absurd” and not ought to be held or defended.

Remained silent until 1627.

Published Il Saggiatore, in which he contended that the new astronomical discoveries were more in accord to the Copernican view than that of Ptolemy.

In addition, he pointed out that, while one was condemned by the Church and the other by reason, a third system would have to be sought.

The book was dedicated to Pope Urban VIII.

It was well received by both the ecclesiastical and scientific community.

In two months, Galileo had six audiences with the pope.

Galileo’s answer to “If the earth moved, everything would blow off.”

His principle of inertia.

If a stone were dropped from the mast of a moving ship, it would hit the deck and not the water because it would be imbued with the forward motion (inertia) of the ship.

Dialogo dei Due Massimi Sistemi (Dialogue on the Two Principal Systems of the World) 1632 (age 68).

Prevailed upon Pope Urban VIII, an old friend, to allow him to publish the book.

Galileo claimed it would only examine the nature of the Copernican system to show other nations that Italians were not ignorant of new theories.

Form of Dialogo.

Written in Italian, not Latin, to reach a mass audience.

A 4 day conversation between three philosophers:

Sagredo – The “impartial” judge.

Salviati – Galileo’s pro-Copernican mouthpiece.

Simplicio – The Aristotlian.

Salviati (Salvation) and Simplicio (Simpleton) constantly argue.

Resolution comes when Sagredo is convinced (always by Salviati).

A thinly disguised disclaimer appears as the book’s preface, which states that the book is a mathematical fantasy and that divine knowledge assures us of the immobility of the earth.

A witty, penetrating discussion of ancient and modern views.

Brilliantly expounded and defended the Copernican theory by focusing in on the weakest point of Aristotle’s physics – its account of the motions of bodies.

The work was condemned and its sale forbidden.

Galileo was summoned before the Inquisition at Rome in 1633 (age 69).

Pope Urban VIII, probably feeling betrayed, did not come to Galileo’s aid.

Three charges:

He had broken his agreement of 1616;

He had taught the Copernican theory as fact; and

He actually believed in the Copernican theory.

Denounced only as a “vehement suspected of heresy”.

Convicted on the evidence of a forged document and forced to recant his belief that the earth moved around the sun.

In 1979, Pope John Paul II proposed reversing the condemnation of Galileo after 346 years.

In 1992, a papal commission acknowledged the Vatican’s error.

As he rose from his knees after his renunciation, legend has it that Galileo whispered under his breath, “but it does move.”

There is now some doubt as to how much Galileo really believed of what he wrote in Dialogo.

Aquinas’ “Dichotomy of faith versus reason” – one cannot have both.

Since Galileo really didn’t have the proof of the heliocentric hypothesis, the subject still remained in the realm of the scriptures.

House arrest.

Treated leniently, but instructed to keep out of the public eye.

Moved to Arcetri on the outskirts of Florence in 1633.

Still, Galileo spent his remaining eight years under virtual house arrest and worked in strict seclusion.

Last telescopic discovery in 1637 (age 73).

Lunar librations – the subtle east-west and north-south rocking of the visible face of the moon.

Went totally blind that same year.

Continued his scientific correspondence and investigation.

Continued his teaching.

In 1638, at the age of 74, he completed Discourses Concerning Two New Sciences.

A recapitulation of his later work in the theory of mechanics.

The manuscript was smuggled out of Italy and published at Leiden in the Netherlands.

Together with Dialogue, it demolished the old and outdated ideas and laid the foundations of the new mathematical physics.

Galileo – Epilogue.

Founder of modern scientific method.

Applied mathematics.

Careful Observation.


Inductive reasoning.

The first modern physical scientist.

Astronomical contributions consisted mainly of telescopic discoveries and were not theoretical in nature.

Most significant contribution was in the field of mechanics.

Did not clearly relate force and motion into definitive laws.

Set the foundation from which Newton could take off.

Why Galileo was more admonished than Kepler.

Galileo was closer to the center of the Church (Rome).

Kepler exiled himself when the going got tough.

Galileo did not care if he told the Church one thing and went and did another.

Kepler could hide his ideas in mathematics.

Mathematics is a formal logic which one can easily prove or disprove.

Mathematics is always not understood by non-specialists.

Galileo had to use rhetoric – much more subjective.

A 1615 letter from an ecclesiastical friend from Rome:

“You can write as a mathematician and hypothetically, as Copernicus is said to have done, and you can write freely so long as you keep out of the sacristy.”


Kepler was more objective and mathematical.

Galileo had an acid tongue, a fiery temper, and sarcastic wit.

His childhood nickname “The Wrangler” was justifiably earned.

There is some question as to whether the Copernicans – Galileo, Kepler, and their contemporaries, had the right in their own day to believe their theory true.

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