I
Galileo shows a young boy named Andrea Sarti, the son of his housekeeper and his future student, the Copernican model of the solar system. Galileo says that it is time for new knowledge, a review of all previous truths and the birth of new ones.
The old Ptolemaic system considers the ground fixed, with reliable support. Now it turns out that there is no support; everything is movable.
The boy does not immediately believe Galileo. However, Andrea repeats this "heresy" in school as a kind of joke. His mother, Galileo’s housekeeper, Mrs. Sarti, does not like it and is surprised when she learns that Galileo put these ideas in Andrea's head. Additionally, she is concerned that Galileo does not pay the milkman and that they have debts.
II
Galileo shows the public his new invention—the telescope—which he learned about from the Dutch. Everybody is excited and Galileo gets an increase in salary.
Any scientific discovery has a "double" meaning. For the uninitiated, this is just a telescope, and has only practical benefits. But scientists understand how closer observation of the stars can have profound effects on society, potentially changing the general worldview.
Ludovico, a rich young man, who wants to study with Galileo, soon learns that these telescopes are already being sold throughout Europe.
III
January 10, 1610. Galileo and his friend Sagredo, look the moon with the telescope. They observe that the moon does not emit its own light, but rather reflects the light from the sun. Galileo says that the Earth is just like the moon: both rely on light from the sun. This is contrary to the idea of a universe centered on the earth.
Galileo and Sagredo observe the moons of Jupiter and confirm the hypothesis of Copernicus. Galileo is delighted and wants to tell people about his discovery, but Sagredo warns him that people will not understand.
Galileo writes a letter to the Grand Duke of Florence, Cosimo de' Medici, and tells him that he will name the moons of Jupiter after the Medici.
IV
Andrea Sarti and Galileo move to Florence and take up residence in the palace of the Medici. Duke Cosimo is of the same age as Andrea. Andrea shows Cosimo the Copernican model of the solar system, but Cosimo prefers the Ptolemaic system. The scholars at the court are unconvinced by Galileo's discoveries, skeptical of anything resembling Copernican thought. They send for the most important astronomer of the Vatican, Christopher Clavius, to check and confirm Galileo's work.
V
While the plague overtakes Florence, Galileo continues his studies, undeterred by the threat of disease.
VI
1616. The "Collegium Romanum," the Vatican Research Institute, confirms Galileo's discoveries.
While waiting for the decision from Clavius, the monks discuss the terrible consequences of accepting the Copernican system.
The cardinal does not accept Galileo's discovery, saying that man is at the center of the universe.
VII
March 5, 1616, the Inquisition imposes a ban on the Copernican theory.
Cardinals Barberini and Bellarmine are trying to persuade Galileo to abandon his theory. They allude to the social significance of his discovery. The Church helps people, especially the common people, to make sense of their lives, and Galileo's views throw their belief systems into doubt. They offer for Galileo to continue his studies but not put forward any conclusions. Galileo is not satisfied.
The Cardinal Inquisitor speaks with Galileo's daughter Virginia, alluding to the ambiguity of her father's position.
VIII
At the palace of the Florentine Ambassador in Rome, Galileo speaks with a little monk. The little monk speaks about his parents, how they live in poverty and justify their suffering through their belief in God. He warns Galileo that his discoveries could create social unrest and chaos, but Galileo believes that science will open the eyes of all people.
IX
Galileo holds off his research for eight years, studying mechanics instead. When he learns that the scientist, Cardinal Barberini, is becoming Pope, he returns to astronomy.
X
During the following decades, the doctrine of Galileo is widely distributed among the people. Pamphleteers and street singers pick up his new ideas. Galileo is proclaimed a destroyer of Catholicism, as well as a hero.
XI
1633. Galileo and his daughter are expected at the reception of the Grand Duke. Virginia warns her father about the Inquisition. Galileo believes that the Duke will approve of his work, but he does not, and Galileo is brought in for questioning in the Inquisition.
XII
The Pope and the Cardinal Inquisitor discuss Galileo's fate.
XIII
Galileo recants on his research, disappointing his students and returning to his life, changed by the trauma of the Inquisition.
Behind the stage, an excerpt from Galileo's book, Discorsi, is projected.
XIV
From 1633 to 1642, Galileo lives in a country house near Florence, a prisoner of the Inquisition.
Andrea visits Galileo on his way to Holland. While visiting with his old teacher, from whom he has become estranged, Galileo gives Andrea his Discorsi and sends him on his way to Holland.
XV
In 1637, Andrea leaves Italy. At the border he is inspected, but the border guards are too lazy to review all of his books. During the inspection, some boys playing nearby are discussing a local witch. Andrea tells them that a human could never fly through the air on a broom.
