The Catholic Church did not explicitly prohibit teaching about sunspots. The situation is more complex and related to the broader conflict between Galileo Galilei and the Church regarding heliocentrism (the idea that the Earth revolves around the sun). Here's a breakdown of the nuances:
* Focus on Heliocentrism: The main issue was Galileo's advocacy for the heliocentric model of the solar system proposed by Nicolaus Copernicus. This contradicted the prevailing geocentric (Earth-centered) view that was supported by the Church and interpreted through certain passages in the Bible.
* Sunspots as Evidence: Galileo's observations of sunspots, published in "Letters on Sunspots," were used as evidence against the Aristotelian view of an immutable and perfect heavens. Aristotle's philosophy, heavily integrated with Church doctrine at the time, held that celestial bodies were flawless. Sunspots suggested imperfections and changes in the sun, challenging this view.
* Indirect Conflict: The Church's opposition to Galileo's sunspot observations wasn't about the sunspots themselves. It was about how Galileo used them to argue against the established cosmological model and, by extension, against the authority of the Church's interpretation of scripture.
* Decree Against Copernicanism: In 1616, the Church declared Copernicanism "false and erroneous" and forbade Galileo from holding or defending it. This decree made it difficult for Galileo to discuss sunspots or any evidence supporting heliocentrism without risking conflict with the Church.
* The Trial of Galileo: Galileo was eventually tried by the Inquisition in 1633 for disobeying the 1616 decree and publishing "Dialogue Concerning the Two Chief World Systems," which defended heliocentrism. He was found guilty of "vehement suspicion of heresy" and sentenced to house arrest.
In Summary: The Catholic Church didn't ban teaching about sunspots directly. However, Galileo's use of sunspot observations to support heliocentrism, which contradicted the Church's accepted geocentric view, led to conflict and ultimately to Galileo's condemnation. The prohibition was against promoting Copernicanism, and discussing sunspots became problematic because they were used as evidence in that debate.