still thinking about the documentaries I listened to described the Kepler-Galileo acquaintance, what was that about
From my understanding it went something like this:
1597: 25 years old maths teacher Kepler sends Mysterium Cosmographicum (in which he uses Copernican system as the basis) to a bunch of people, mostly gets ignored - Galileo, a 31 years old professor at the University of Padua, alone sends him a VERY enthusiastic letter back, in which he expresses gratitude for the beginning of friendship, that he subscribed to the teachings of Copernicus for many years (he says "our master Copernicus"), and that he will study Kepler's book carefully - This is the EARLIEST proof we have of Galileo's Copernican views. Galileo publishes his own Copernican views for the first time 13 years later. - Kepler sends another letter back, ending with "Farewell, and answer me with a very long letter" - Galileo never writes back - Kepler tries a couple more times to send letters to Galileo, and not hearing back, gives up after a while
In the meantime Kepler started working for Tycho Brahe, and after Brahe's death takes over his position as the Imperial Mathematician to Emperor Rudolf II
1609: Kepler publishes Astronomia Nova, in which he presents very strong arguments for heliocentrism. In an open letter, he asks Galileo for a review but doesn't receive one. Also considering that Kepler presents a very strong argument for ecliptic orbit of the planets, while up until death Galileo believed in the uniform circular orbit, who knows whether he even read it
1610: Galileo publishes Sidereus Nuncius (Starry Messenger), a first publication based on observations through a telescope (that the milky way is composed of myriad stars, that the moon's surface has valleys and mountains, that Jupiter has 4 moons). He sends a copy to the imperial court, requesting comments from Kepler - Kepler publishes Dissertatio cum Nuncio Sidereo (Conversation with the Starry Messenger), an open letter endorsing Galileo's findings, giving him credibility - he's the first astronomer to do so. (In it, Kepler also asks: "I should rather wish that I now had a telescope at hand") - Galileo sends a letter to Kepler, thanking him for his support and open-mindedness, calling him "my Kepler" and laughing at closes-mindedness of other professors. - This is the very last letter Galileo would ever send to Kepler. - Galileo did build a small number of telescopes, but he didn't send any to his earliest and biggest supporter the Imperial Mathematician Kepler (nor did he send any to Emperor Rudolf II despite being requested so at another time) - Later that year, Kepler manages to borrow the telescope, and based on his own observations, publishes Narratio de Observatis Quatuor Jovis Satellitibus, giving even more credibility to Galileo
1611: Kepler publishes Dioptrics, in which he improves the design of the telescope. Additionally, he brings up two anagrams that Galileo sent to the imperial court the past years to solve - both were hints at additional discoveries that Galileo made after the publications of the Starry Messenger. Kepler wasn't able to solve either, but Galileo sent solutions to the imperial court: the first one stating that Saturn has rings, the second - that Venus waxes and wanes like the Moon. Thus for the 3rd time, Kepler gave credibility to Galileo.
After that, Kepler started going through many personal tragedies and eventually died in 1630, and Galileo through many personal controversies that led to his trial; but there happened one more mention of Kepler by Galileo:
1632 Galileo wrote Dialogue Concerning the Two Chief World Systems, in which he's so focused on proving Earth's revolution around the sun that he explains the tides not by gravity, in which he didn't believe, but by Earth's rotation. In contrast, Kepler believed that the moon is causing the tides. In the book, Galileo addresses this: "But among all the great men who have philosophized about this remarkable effect, I am more astonished at Kepler than at any other. Despite his open and acute mind, and though he has at his fingertips the motions attributed to the earth, he has nevertheless lent his ear and his assent to the moon’s dominion over the waters, to occult properties, and to such puerilities"
I forgot to add around 1611 Galileo recommended Kepler as his successor at University of Padua, but on the account of his wife's failing health, Kepler preferred to stay closer to home
