Chronology
The Great Celestial Discoveries
1609-1613
On
January 7, 1610 Galileo announced to Antonio de' Medici the results of his
telescopic observations, mentioning in particular the "rough and uneven"
surface of the Moon and the discovery of three heavenly bodies in the vicinity
of Jupiter. On the 13th of the same month, he discovered a fourth. The newly
discovered moons were called "Medicea Sydera" in honor of the reigning house of
Tuscany. To determine the position of the satellites without having to carry
out complex calculations every time, Galileo developed a special instrument,
called the giovilabio.
On
March 12 of that same year he published in Venice the Sidereus Nuncius [Starry
Messenger] (Venice, 1610), dedicated to Grand Duke Cosimo II, the work that
made known to the world the extraordinary innovations introduced to astronomy
thanks to the telescope. Towards the end of July the scientist, who had already
resigned from his Chair at Padua to return to Tuscany as First Mathematician
and Philosopher to the Grand Duke, conducted observations on Saturn, which
seemed to him to consist of a central core with two lateral parts joined to it.
Due to its strange shape, Galileo described the planet as "tricorporeo", or
triple-bodied. In August he also conducted observations on sunspots and then,
in the last months of the year, he saw for the first time the phases of Venus,
rightly judging that he had found a decisive factor for confirming the
Copernican system.