"I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use." "Take note theologians, you run the risk of some day having to condemn as heretics, those who would declare, as you do, that the Earth stands still." ~ Galileo Galilei

Galileo Galilei

Galileo Galilei was born on February 15, 1564 and died on January 8, 1642 (aged 77). He was an Italian physicist, mathematician, astronomer, philosopher, and author. He was one of the pioneers of the Scientific Revolution. His major contribution to observational astronomy was the improvement to the telescope, which led to his support of Copernicus. Copernicanism theorized that the Sun was the center of the universe, not the Earth. Galilei would expand on Copernicus original hypothesis and suggest that, not only was the Earth not the center of the universe, it was not even the center of our Solar System; the Sun was the center. Other contributions include the telescopic confirmation of the phases of Venus, discover of the four largest satellites of Jupiter (later referred to as the Galilean Moons), observation and analysis of sunspots (caused by intense magnetic activity), inventing an improved military compass, and various other ground-breaking discoveries.


Most people during Galileo's lifetime subscribed to Geocentrism, a geocentric model, or the Ptolemaic system, which describes the cosmos where planet Earth is at the orbital center of all celestial bodies.

As Galileo prepared to write his literature in support of Copernicus, he made a 2-week journey to Rome to meet with his old friend, Pope Urban VIII. They talked about whether or not Galileo could publish the Copernican theory. He was told that as long as he limits himself to speaking about it hypothetically, there would be no problem. So as long as the Copernican view, that the Earth moved around the sun, was presented only as a hypothesis, one theory among many, Urban the 8th would allow it to be debated. Galileo came away from this meeting feeling like this was the right time to publish his book on Cosmology and the Copernican world view.

He began writing the book at 60 years of age and after 5 years, he finished on Christmas eve, 1629. His book was entitled, "Dialogue Concerning the Two Chief World Systems: Ptolemaic and Copernican" (see characters below). The narrative is between three spirited characters, noblemen of Venice. The first character, the host, prompts a debate between his two talkative guest. One of the visitors clearly speaks up for Copernicus and Galileo, the other guest, "Simplicio," the simpleton, is a comic foil, mouthing the churches doctrine on Science and Philosophy.

Galileo got permission from a friendly sensor in Florence. He knew the sensors in Rome would be much more difficult to persuade. While Galileo waited for results, copies of his dialogue were quietly passed among powerful Roman churchman. Curiously, Galileo's great admirer, the Pope, may not have actually read it, but heard rumors. Rumors that Galileo had not written a scientific discourse, but a literary satire. What Galileo was doing was writing a work of great literature. He wrote it as a dialogue so that it would be both a scientific and literary work and was expecting that this most cultured, cosmopolitan and progressive of Popes would appreciate it. At the end, the words of the Pope came from the mouth of the simpleton, "if God wanted to make the universe some other way, any other way, but make it appear to us, the way it does now, he could have. Therefore, none of these arguments on whether the Earth is the center of the universe can be definitive. Pope Urban's advisors persuaded him that he had been the model for Simplicio and that he was being made a fool.

Urban took a very angry view of the book and the two never spoke again. A special commission was convened to look at the manuscript and this commission recommended a process by the Inquisition. He was ordered to appear in Rome by October of that year. He delayed the trip, claiming ill health, until he was ordered to appear again in December. He could come voluntarily, or, he could come in chains. For months his summons to the inquisition did not appear. His trial order finally arrived in April. He was 70 years old.

The Inquisition limited the trial to two questions of fact:

  1. Did the late Cardinal Bellarmine forbid Galileo to advocate Copernicus when the two faced each other, 16 years earlier (in the year 1616)?

  2. Had Galileo violated the Cardinals injunction by writing his dialogue?

Galileo's reply was that he believed the Cardinal stated that it was possible to hold the position hypothetically. He was forced into a position of false humility. Galileo was remanded to a small room in the palace of the Inquisition (detained in the chambers of the "Holy Office"). His dialogue would be banned, and his punishment awaited. The Inquisition determined that he violated the agreement made in 1616.

The Hubble Deep Field (HDF) is an image of a small region in the constellation Ursa Major, constructed from a series of observations by the Hubble Space Telescope. It covers an area 2.5 arcminutes across, about one 24-millionth of the whole sky, which is equivalent in angular size to a 65 mm tennis ball at a distance of 100 metres.

The image was assembled from 342 separate exposures taken with the Space Telescope's Wide Field and Planetary Camera 2 over ten consecutive days between December 18 and December 28, 1995.

Three years after the HDF observations were taken, a region in the south celestial hemisphere was imaged in a similar way and named the Hubble Deep Field South.

The similarities between the two regions strengthened the belief that the universe is uniform over large scales and that the Earth occupies a typical region in the universe (the cosmological principle).

A wider but shallower survey was also made as part of the Great Observatories Origins Deep Survey. In 2004 a deeper image, known as the Hubble Ultra-Deep Field (HUDF), was constructed from a total of eleven days of observations.

The HUDF image was at the time the most sensitive astronomical image ever made at visible wavelengths, until the Hubble Extreme Deep Field (XDF) was released in 2012

The path Galileo followed to the chambers where he would hear his sentence led through the cloisters of Santa Maria sopra Minerva. The paintings on the walls and ceilings warned heretics of the fate that might await them. In the judgment of the "Holy Office", Galileo was vehemently suspected of heresy, namely, having held and believed a doctrine which is false, and contrary to scripture. That the Sun is the center of the world, and does not move; that the Earth is not the center of the world, and does move, we condemn you to formal imprisonment, at this 'Holy Office'.

Galileo was given a chance to renounce his errors, and rather than spending the rest of his life in a dungeon, the 70-year-old Galileo knelt as ordered, and sweared that he believed in the teachings of the scriptures.

Waiting in the Tuscan embassy, he would not know for months when he would be allowed to return home. Dialogue on the Two Chief Systems of the World was added to the index of prohibited books, where it would remain for the next 200 years.

Galileo believed that Pope Urban VIII would protect him from censure, but he did not. At the time, the Pope had his hands full with the 30-years-war. His entire rein was under the shadow of a vicious civil war that was ripping apart the Christian world. When Galileo came to trial Urban could not risk defending his friend, when he personally was under such scrutiny, thus Galileo became expendable. 6 months after his trial, Galileo would finally be allowed to return home. He was not executed because of the pleas of the Tuscan ambassador, the intervention of the Medici family, and the quiet influence of his daughter, Maria Celeste.

Galileo Galilei was confined to his home. He was prohibited from teaching or traveling, even to see his own daughter, without permission from the Church. He was ordered to recite "prayers of penitence" each week. During his long ordeal, with his daughter assisting every step of the way, she took ill. Maria Celeste succumbed to dysentery, at the age of 33. When she died, it was if a light had gone out in Galileo's life.

Many of Galileo's personal letters have survived, but not one of the letters he wrote to his daughter have ever been found. Today, we only have her side of their communication. He definitely answered her letters, and she saved many of his. More than likely, the letters were destroyed.

The Inquisition chose to ban Galileo's dialogue, but it was powerless to ban his ideas. In 1992, a papal commission, reconsidered it's handling of the Galileo affair. Pope John Paul II stated that faith should never conflict with reason, and he used the very words Galileo had once written, in his own defense, he believe that the scriptures could never err, but theologians could err in their interpretation of the scriptures. The Pope expressed the churches regret, that the Galileo affair contributed to a tragic mutual misunderstanding between religion and science.

Dialogue Concerning the Two Chief World Systems

Dialogue Concerning the Two Chief World Systems is presented as a series of discussions, over a span of four days, among two philosophers and a layman:

  • Salviati argues for the Copernican position and presents some of Galileo's views directly, calling him the "Academician" in honor of Galileo's membership in the Accademia dei Lincei. He is named after Galileo's friend Filippo Salviati (15821614).

  • Sagredo is an intelligent layman who is initially neutral. He is named after Galileo's friend Giovanni Francesco Sagredo (15711620).

  • Simplicio, a dedicated follower of Ptolemy and Aristotle, presents the traditional views and the arguments against the Copernican position.

  • He is supposedly named after Simplicius of Cilicia, a sixth-century commentator on Aristotle, but it was suspected the name was a double entendre, as the Italian for "simple" (as in "simple minded") is "semplice".

  • Simplicio is modeled on two contemporary conservative philosophers, Ludovico delle Colombe (1565-1616), Galileo's fiercest detractor, and Cesare Cremonini (15501631), a Paduan colleague who had refused to look through the telescope.

  • Colombe was the leader of a group of Florentine opponents of Galileo's, which some of the latter's friends referred to as "the pigeon league".


Galileo Galilei Quotes:

  • It vexes me when they would constrain science by the authority of the Scriptures, and yet do not consider themselves bound to answer reason and experiment.

  • I do not feel obliged to believe that the same God who has endowed us with sense, reason, and intellect has intended us to forgo their use.

  • The sun, with all those planets revolving around it and dependent on it, can still ripen a bunch of grapes as if it had nothing else in the universe to do.

  • Facts which at first seem improbable will, even on scant explanation, drop the cloak which has hidden them and stand forth in naked and simple beauty.

  • By denying scientific principles, one may maintain any paradox.

  • All truths are easy to understand once they are discovered; the point is to discover them.

  • There are those who reason well, but they are greatly outnumbered by those who reason badly.

  • Nothing physical which sense-experience sets before our eyes, or which necessary demonstrations prove to us, ought to be called into question (much less condemned) upon the testimony of biblical passages.