Newly discovered letter by Galileo shows that he lightly edited his original words to appease the Catholic Church

That’s the story as it’s traditionally told. So what has changed? At issue is Galileo’s 1613 letter to mathematician Benedetto Castelli at the University of Pisa. It’s the first known instance when Galileo argued in favor of the Copernican model and that scientific observations should supersede church teaching in regards to astronomy. That letter was copied and circulated widely (a common practice in the 1600s), and a copy found its way into the hands of a tattle-tale Dominican friar named Niccolò Lorini. Aghast at the heretical implications, Lorini forwarded the letter to the Inquisition in Rome on February 7, 1615. It’s currently housed in the Vatican Secret Archives.

Here’s where things get complicated. Galileo asked Castelli to return his original 1613 letter to him. He then wrote to a Roman cleric friend, Piero Dini, on February 16, 1615, claiming that Lorini (in “wickedness and ignorance”) had doctored the copy of the letter forwarded to the Inquisition to make Galileo seem guilty of heresy. He enclosed a different version of the Castelli letter, with notably less inflammatory language, claiming it was the correct version.

Historians were unsure which of the two versions was correct, since the original was deemed lost—until Ricciardo stumbled across it hiding in plain sight in the Royal Society archives. According to Ricciardo, the catalog listed the date of the letter as October 21, 1613, but the actual letter is dated December 21, 1613. This may be why so many prior scholars had overlooked it. It’s also an unusual item for the Royal Society to have in its archives. The Society is currently trying to trace its provenance to determine how it ended up there.

The time when the Catholic Church reigned supreme with the Inquisition still running strong must have been absolutely terrifying, especially as a scholar. I can't say I really blame Galileo for trying to turn it around and accusing the friar of fabricating the evidence against him.

Incidentally, it appears Wikipedia now may need some updating:
https://en.wikipedia.org/wiki/Catholic_Church_and_science#Galileo_Galilei
https://en.wikipedia.org/wiki/Galileo_Galilei#Controversy_over_heliocentrism

And also incidentally and only tangentially related, there is a really good YouTube channel by Brady Haran (creator of Numberphile, Computerphile, etc) called Objectivity, where he explores the Royal Society archives with the head curator there along with the occasional guest. If you're interested in this sort of science related archival stuff; old letters, donated relics, etc. it's a good channel to check out. Two of my favorite episodes were from when Destin from SmarterEveryDay visited the UK and was on the show:
https://www.youtube.com/watch?v=JEZBRbnqXXs
https://www.youtube.com/watch?v=R1vptTqtaB0

A set of nested spheres (called “epicycles”) surrounded the Earth, each an orbit for a planet, the Sun, the Moon, or the stars.

It's only a little thing, but the epicycles were actually extra circles added to the main spheres to explain the occasional retrograde motions of the planets.

If the planets were in simple circular orbits around Earth, they should have just kept going in one direction: forward, or prograde. However, occasionally, they move backward, or retrograde, in our sky. The solution to that was to add little circles, or epicycles, to the main circles, to explain why the planets occasionally moved backwards.