Galileo’s Defense of Heliocentrism
Galileo and the Scientific Revolution
Galileo Galilei is a highlight of the scientific revolution that began in astronomy. Key figures included Copernicus, Brahe, Kepler, Galileo, and eventually Newton. The astronomical revolution marked the transition from the Aristotelian-Ptolemaic universe, based on a geocentric model, to the Copernican, based on a heliocentric model. Galileo laid the foundations for a new physics, supplemented later by Newton, according to the heliocentric view. This new physics was built on a detailed study of motion (uniform, uniformly accelerated, and violent), defined quantitatively using mathematical language.
Defending the Sun-Centered Universe
Topic: Defense of the heliocentric theory: the Sun is at the center of the universe and Earth rotates around it. This thesis generated many enemies, including theologians and the Church’s official position.
Main Ideas
The author defended the following, which led to his discrediting: The Sun is stationary at the center of the spheres’ revolution, and the Earth moves on itself and revolves around the Sun.
He defended this by refuting the arguments of Ptolemy and Aristotle (geocentric model) and adding new arguments against them.
Among the arguments against the Ptolemaic system, he referred to natural effects whose causes could only be explained by heliocentrism, and to recent celestial astronomical discoveries.
His accusers, he noted, were trying to protect the fallacies and false arguments of their speeches through the cloak of religion and Scripture.
Understanding the Ideas
Galileo wrote this long letter (around 1615) to the Grand Duchess when he learned that his enemies were trying to convince his patrons, the Grand Dukes of Tuscany. In it, he admirably develops his arguments in favor of the orthodoxy of the Copernican system, as shown by the text’s theme: the Sun motionless at the center of the universe, and the Earth moving on itself and revolving around it.
The author defends this thesis by refuting the arguments of Ptolemy and Aristotle, who represented the geocentric model, and by adding new arguments against this model. He argued that many natural and astronomical phenomena could not be explained by the Ptolemaic system but only through the heliocentrism he defended.
Evidence from Telescopic Discoveries
He supported his heliocentric explanation with findings obtained through the telescope, such as:
- Mountains on the Moon
- Sunspots
- The moons of Jupiter
- The phases of Venus
Interpreting Scripture and Nature
Similarly, in this letter, Galileo attempted to dismantle the geocentric system, arguing that the Sacred Book (the Bible) is also the book of nature, and both were created by God. The question, he argued, was how to interpret what the Bible says, as it is a literary work that uses metaphors. Galileo argued that science offers the correct way to interpret the universe.
Opposition and Church Condemnation
Finally, he stated that his accusers were trying to protect the fallacies and false arguments of their speeches through the cloak of religion and Scripture. These fallacies were used against something they did not understand.
In this connection, it should be noted that Galileo’s major effort in this letter to defend his heliocentric view of the universe was driven, at the same time, by the desire that the Church not endorse erroneous doctrines. Despite all that effort, he could not avoid the condemnation of the Copernican theory by the Inquisition in February 1616.
Later, in 1633, he would be convicted again and forced into retraction for ridiculing the advocates of the geocentric system in his Dialogue Concerning the Two Chief World Systems (1632).