Reading Revolutions: Intellectual History

What We Have Here is a Failure to Communicate: Galileo and the Church

Christopher Magri

The following is a summary of a lecture given by Chris Magri based on his slides.

As the story goes, Copernicus proposed a heliocentric solar system in De Revolutionibus Orbium Coelestium  which was published after his death.  The Church is outraged and threatened by the new science.  Galileo is persecuted for defending the Copernican model, defiantly publishes Dialogue on the Two Chief World Systems and ends his life under house arrest.  The history is more complicated and much more ambiguous.

In the 1500's the understanding of the heavens were based on the writings of Aristotle and the model created by Ptolemy in the second century.  Using observations of gravity and motion, the Aristotelian model proposes a geocentric universe. 

The model fits most observations.  Without modern measurement it is difficult to prove otherwise.  It also fits nicely with personal egocentrism and the theology of the Church.  There are anomalies. 

The predictable but rather arbitrary motion of the planet Mars is illustrated by a chart created by Chris Magri.  Of course, it is only arbitrary if you assume Mars is revolving around the earth.

Ptolemy explained the phenomenon of retrograde motion by proposing epicycles.

In addition, the earth would be off-center in relation to the path to account for changes in distance.

Over time, the epicycle would be displaced.

Anonymous author.  See model in motion at:'s Model.htm

When you add in the other four planets, you have what appear to be spinning rings on orbits.  You can see the effect in this computer model from Paul Stoddard.  Click on the link below, choose months, and change the speed on the slider in the upper right hand corner to observe both what we see from earth and what the motion would look like if seen from above.

By permission of Paul Stoddard:  See model in motion at

When Copernicus proposed that the sun is central he did not simplify the mathematics.  The model still requires epicycles.

Notice that the orbits are perfect circles.  Copernicus felt that this was consistent with the ideal of harmony in the universe but it made his model difficult to describe.

By permission of Paul Stoddard:  See model in motion at


For the Church, the main purpose of astronomy was to predict the position of the planets and thus set the time for the moveable feast days.  Thus, the forward suggests that the Copernican model may be a convenient fiction, acceptable if it works.  (Take a look at the calculations for Easter).

Copernicus did not make many observations of his own, instead he relied on the observations of the ancients and his interpretation of Plato.  Tycho Brahe, on the other hand, spent his life making extensive and exacting observations of planetary, solar, and stellar positions.

Brahe, concluded that the earth doesn't move because if it did, if you measured the stars when the earth was on one side of the sun and contrasted those measurements to measurements made when the earth moved to the other side of the sun, closer stars would change their position relative to farther stars.  This is called stellar parallax. 

It is similar to binocular parallax.  Hold your finger out in front of you, close one eye and then the other and look at your finger.  The finger moves in relation to the objects behind it because your eyes are inches apart.  Brahe was unable to find any evidence that parallax occurred in any of his extensive records.  While the distance between the positions of the earth are great, the stars are so far away that the parallax effect is extremely small.  Measurements of stellar parallax were not successfully made until 1838 by Friedrich Bessel.

By permission of Paul Stoddard:  See model in motion at

Galileo ignored Brahe's model and chose to support Copernicus.

Galileo was not the only scientist in the 1600's.  There was a network of individuals across Europe who both corresponded and shared publications.  Galileo was one of the first to use the telescope and in 1611 used one to show sunspots to a number of people in Rome.  In October of 1611, a Jesuit, Scheiner, began to make observations of sunspots and published his findings in January 1612.  He interpreted the sunspots as small planetoids revolving around the sun. 

After that, Galileo began a serious study of sunspots and carried out a series of debates with Scheiner, a member of the Jesuit order, in published letters.  Galileo challenged Scheiner's interpretation and provided measurements and observations to prove that the spots were blemishes on the sun and that they showed that the sun rotates.  Scheiner lost the debate and in subsequent publications changed his interpretation to agree with Galileo.  Years later, Galileo complained that other scientists were trying to claim primacy in the discovery of sunspots -- credit for which Galileo felt belonged to him.  Scheiner assumed that Galileo was talking about him and was outraged.  Galileo had a new enemy. 

He was able to go on to alienate all of the Jesuits when he scathingly called their intelligence and integrity into question over the nature of comets.  Jesuit observers had proposed that comets were short-lived planetary objects in orbit while Galileo claimed they were vapors in the earth's atmosphere.  Galileo could not limit himself to proof and observations but felt compelled to vilify anyone who disagreed with him.

Galileo's more reasoned style can be read in his letter to the Grand Duchess Cristina expressing his views on the relationship between science and Biblical interpretation:

Galileo posits that the denial of the Copernican theory has more to do with Galileo's defense of Copernicus since the Copernican theory had been read and discussed without problem for over 50 years.  He calls on the writings of St. Augustine to show that enquiry and reason can be brought to bear on biblical issues and that literalism can be used in both directions.

Magri goes on to give illustrations of places where it is absurd to take the Bible literally, even without touching on scientific matters:

Opposition against Galileo and by extension, his theories, grows.  It is not limited to people within the Church but is found among academics who have been insulted, threatened, or refuted by Galileo in various publications on a vast array of topics.  Cardinal Bellarmine is sent to warn Galileo not to promote the Copernican model but to treat it as an hypothesis.  Caution is the word.

Pope Urban VIII suggests that Galileo consider that God might have made the world one way but allowed us to see it in another way.  Galileo gets permission to publish a work about Copernican theory as long as it is clearly treated as unproven.

The use of a conversation to explore different sides to an issue allows Galileo to seem even-handed. The personalities and arguments he assigns his characters are anything but unbiased, in fact, they strengthen the insults directed at Aristotelian and Ptolemaic astronomy.  He is even able to include a passing insult directed toward Scheiner. 

To answer Cardinal Bellarmine's demand for evidence, Galileo has Salviati argue in the Dialogue that the presence of ocean tides proves that the earth moves. 

Pope Urban VIII is not amused and probably feels betrayed.  He turns from supporter to judge.  He orders that the Inquisition investigate.  Where he had admired and sought to counsel Galileo on handling his enemies, now he joined them in seeing Galileo as totally out of control and a threat.

The Catholic church continued to produce great scientists and removed itself from the controversies over stellar configurations.  It was even able to absorb Darwin's evolution.  The same cannot be said of all.  Some still fear that knowledge may undermine belief.  

Now they want belief to be disguised as science rather than science subsumed under belief.  It leads to:

and also to:


Kepler published Epitome Astronomiae in 1621 in which he provided extensive mathematical proofs of the Copernican heliocentric solar system as modified by Kepler to include elliptical orbits.  Kepler's work did not attract the same kind of hysterical opposition.  Earlier, Kepler attempted to share his findings with Galileo, but Galileo was on his own road. 

Galileo's response to critics and to colleagues alike played an important part in the polarization of emotion and politics.  Had he been able to restrain himself to his more reasoned arguments he may have been able to maintain the support of those both in the Church and in academia who had once defended and admired him.

As Galileo ended his Dialogue with the words of Sagredo:

so we must end.


The 1710 Florence edition of Dialogo di Galileo Galilei linceo matematico supremo dello studio di padova Click either picture for an enlargement.

An English translation of the work can be found at


"What We Have Here is a Failure to Communicate:  Galileo and the Church."  Summary of a lecture by Christopher Magri.  University of Maine at Farmington, September 14, 2005.  Retrieved _______.   <>.


Marilyn Shea, 2005