The Galileo affair (Italian: il processo a Galileo Galilei) began around 1610 and culminated with the trial and condemnation of Galileo Galilei by the Roman Catholic Inquisition in 1633. Galileo was prosecuted for his support of heliocentrism, the astronomical model in which the Earth and planets revolve around the Sun at the centre of the Solar System.
In 1610, Galileo published his Sidereus Nuncius (Starry Messenger), describing the surprising observations that he had made with the new telescope, among them, the Galilean moons of Jupiter. With these observations and additional observations that followed, such as the phases of Venus, he promoted the heliocentric theory of Nicolaus Copernicus published in De revolutionibus orbium coelestium in 1543. Galileo's discoveries were met with opposition within the Catholic Church, and in 1616 the Inquisition declared heliocentrism to be "formally heretical." Heliocentric books were banned and Galileo was ordered to abstain from holding, teaching or defending heliocentric ideas.
Galileo went on to propose a theory of tides in 1616, and of comets in 1619; he argued that the tides were evidence for the motion of the Earth. In 1632 Galileo published his Dialogue Concerning the Two Chief World Systems, which implicitly defended heliocentrism, and was immensely popular. Responding to mounting controversy over theology, astronomy and philosophy, the Roman Inquisition tried Galileo in 1633 and found him "vehemently suspect of heresy", sentencing him to indefinite imprisonment. Galileo was kept under house arrest until his death in 1642.
In astronomy, the geocentric model (also known as geocentrism, often exemplified specifically by the Ptolemaic system) is a superseded description of the Universe with Earth at the center. Under the geocentric model, the Sun, Moon, stars, and planets all orbited Earth. The geocentric model was the predominant description of the cosmos in many ancient civilizations, such as those of Aristotle in Classical Greece and Ptolemy in Roman Egypt.
Two observations supported the idea that Earth was the center of the Universe:
Ancient Greek, ancient Roman, and medieval philosophers usually combined the geocentric model with a spherical Earth, in contrast to the older flat-Earth model implied in some mythology.[n 1][n 2] The ancient Jewish Babylonian uranography pictured a flat Earth with a dome-shaped, rigid canopy called the firmament placed over it (רקיע- rāqîa').[n 3][n 4][n 5][n 6][n 7][n 8] However, the Greek astronomer and mathematician Aristarchus of Samos (c. 310 – c. 230 BC) developed a heliocentric model placing all of the then-known planets in their correct order around the Sun.
Heliocentrism[a] is the astronomical model in which the Earth and planets revolve around the Sun at the center of the Solar System. Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center. The notion that the Earth revolves around the Sun had been proposed as early as the 3rd century BC by Aristarchus of Samos, but at least in the medieval world, Aristarchus's heliocentrism attracted little attention—possibly because of the loss of scientific works of the Hellenistic Era.[b]
It was not until the 16th century that a mathematical model of a heliocentric system was presented, by the Renaissance mathematician, astronomer, and Catholic cleric Nicolaus Copernicus, leading to the Copernican Revolution. In the following century, Johannes Kepler introduced elliptical orbits, and Galileo Galilei presented supporting observations made using a telescope.
Nicolaus Copernicus (/koʊˈpɜːrnɪkəs, kə-/; Polish: Mikołaj Kopernik;[b] German: Nikolaus Kopernikus; Niklas Koppernigk; 19 February 1473 – 24 May 1543) was a Polish Renaissance-era mathematician and astronomer, who formulated a model of the universe that placed the Sun rather than Earth at the center of the universe, in all likelihood independently of Aristarchus of Samos, who had formulated such a model some eighteen centuries earlier.[c][d]
The publication of Copernicus' model in his book De revolutionibus orbium coelestium (On the Revolutions of the Celestial Spheres), just before his death in 1543, was a major event in the history of science, triggering the Copernican Revolution and making a pioneering contribution to the Scientific Revolution.
Copernicus was born and died in Royal Prussia, a region that had been part of the Kingdom of Poland since 1466. A polyglot and polymath, he obtained a doctorate in canon law and was also a mathematician, astronomer, physician, classics scholar, translator, governor, diplomat, and economist. In 1517 he derived a quantity theory of money—a key concept in economics—and in 1519 he formulated an economic principle that later came to be called Gresham's law.[e]