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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Copernican Revolution | 2/5 | https://en.wikipedia.org/wiki/Copernican_Revolution | reference | science, encyclopedia | 2026-05-05T12:41:57.697069+00:00 | kb-cron |
Copernicus' challenge reached 16th-century astronomers but failed to displace the dominance of Ptolemy's geocentrism, which only fell out of favor among astronomers after Galileo's telescopic observations of 1610. But Copernicanism did gain a handful of supporters in the 16th century. Thomas Digges and Giordano Bruno used Copernicus' new estimate of the distance to the stars to argue for an indefinitely extended or even infinite universe in opposition to the ancient orthodoxy of celestial spheres. William Gilbert also argued (correctly) that Copernicus was right about the Earth rotating on its axis (instead of an outer "shell" of rotating stars) while also arguing (incorrectly) that the mechanism of the Earth's rotation is magnetism. The science historians Herbert Butterfield, Arthur Koestler, Otto Neugebauer and David Wootton all emphasize that, from a strictly scientific point-of-view, Copernicus' work should not be considered revolutionary.
=== Protestant Attacks ===
Copernicus was a canon, a lifelong official of the Catholic Church. Even before his death in 1543 and during the following 70 years (until 1610), his model faced withering criticism from Protestant leaders who were locked in combat with the Church, were often animated by a fierce anti-clericalism and typically adopted a literalist approach to Scripture. Protestant leaders Martin Luther and Philip Melanchthon both attacked Copernicus. Luther famously cited the Book of Joshua to prove the sun moves and reportedly called Copernicus a "fool." His colleague Melanchthon urged governments to repress the "absurd" theory. Meanwhile, the Catholic Church indirectly used Copernican mathematics in its reform of the Gregorian calendar in 1582 and otherwise, until 1610, remained officially silent on either the merits or demerits of Copernicanism.
=== Telescope ===
Galileo Galilei, sometimes referred to as the "father of modern observational astronomy," developed his own telescope with enough magnification to allow him to study Venus and discover that it has phases like a moon. His improvements to the telescope, astronomical observations, and support for Copernicanism were all integral to the Copernican Revolution. Based on the designs of spectacle-maker Hans Lippershey, Galileo designed his own telescope which, in the following year, he had improved to 30× magnification. Using this new instrument, Galileo made a number of astronomical observations which he published in the Sidereus Nuncius in 1610. In this book, he described the surface of the Moon as rough, uneven, and imperfect. He also noted that "the boundary dividing the bright from the dark part does not form a uniformly oval line, as would happen in a perfectly spherical solid, but is marked by an uneven, rough, and very sinuous line, as the figure shows." These observations challenged Aristotle's claim that the Moon was a perfect sphere and the larger idea that the heavens were perfect and unchanging. Galileo's next astronomical discovery would prove to be a surprising one. While observing Jupiter over the course of several days, he noticed four stars close to Jupiter whose positions were changing in a way that would be impossible if they were fixed stars. After much observation, he concluded these four stars were orbiting the planet Jupiter and were in fact moons, not stars. This was a radical discovery because, according to Aristotelian cosmology, all heavenly bodies revolve around the Earth and a planet with moons obviously contradicted that popular belief. While contradicting Aristotelian belief, it supported Copernican cosmology which stated that Earth is a planet like all others. In 1610, Galileo observed that Venus had a full set of phases, similar to the phases of the moon we can observe from Earth. This was explainable by the Copernican or Tychonic systems which said that all phases of Venus would be visible due to the nature of its orbit around the Sun, unlike the Ptolemaic system which stated only some of Venus's phases would be visible. Due to Galileo's observations of Venus, Ptolemy's system became highly suspect and the majority of leading astronomers subsequently converted to various heliocentric models, making his discovery one of the most influential in the transition from geocentrism to heliocentrism.
=== Trials of Galileo ===
Galileo's Letters on Sunspots, published in 1613, defended the view that sunspots are features of the Sun's surface but also reported his 1610 telescopic observations of the full set of phases of Venus. In his 1615 Letter to the Grand Duchess Christina, Galileo argued that the language of the Bible had been accommodated to be understandable to uneducated people and should therefore not be interpreted as literal scientific descriptions and the Church risked reputational damage in the long run if it officially condemned heliocentrism. Galileo received staunch support from a Carmelite friar, Paolo Antonio Foscarini, who published a book defending Galileo's work and presenting it as compatible with the Bible, but also bitter opposition from some philosophers and clerics, two of whom denounced him to the Roman Inquisition early in 1615, warning "that Galileo should not go outside mathematics and physics and should avoid provoking theologians by teaching them how to read the Bible". The Dominican friar and preacher Tommaso Caccini both issued a complaint to the Inquisition and also attacked Galileo in sermons, ordering him to withdraw from philosophy and citing Acts 1:11: "Ye men of Galilee, why stand ye gazing up into heaven?". The report of the Inquisition's consultants declared heliocentrism as "false and contrary to Scripture" in February 1616. The Church demanded Galileo stop teaching and defending Copernican theory, to which Galileo agreed. In March, the Church's Congregation of the Index issued a decree suspending De revolutionibus until it could be "corrected." The edits to De revolutionibus, which omitted or altered nine sentences, were issued four years later, in 1620. A second trial in 1633 led to Galileo's house arrest and a ban on his books.
== Profane universe ==