When Cosimo became ruler, he helped sponsor Galileo's research.
And these moons were called by Galileo, we call them the
Galilean moons, but Galileo called them the Medicean moons, after his sponsor.
And, one of the things I strongly recommend doing is taking your own
telescope if you have access to one, or even a pair of good binoculars, and
looking at Jupiter.
And if you look at Jupiter, what you'll see, just like Galileo, are these moons.
These moons move fairly quickly.
So if you observe Jupiter night to night,
you will see the position of these moons change.
And you can track the moons, and do what Galileo
did, and discover that they, too, orbit around a planet.
Before going on to talk about
the moons' properties, I just wanted to bring up this wonderful quote that I got
from the Medici Archives. To me, this represents one of the best
pieces of playing up to your sponsor that I've ever seen.
I just love this.
So I'm going to read this to you.
Behold, therefore, four stars reserved for your illustrious name.
Remember, that Galileo were, named these after Medici.
And not of the common sort and multitude of the less notable fixed stars, but the
illustrious order of wandering stars. Wandering stars are, of course, planets.
And what Galileo realized is that these moons,
like planets, were nearby objects moving through the sky.
Which, indeed make their journeys
in orbits with the marvelous speed around the star of Jupiter.
As I noted, if you watch these planets night to
night, you will see how rapidly they move around Jupiter.
The most noble of them all, with mutually different motions,
like children of the same family while meanwhile, altogether, in
mutual harmony, complete their great revolutions every 12 years
around the center of the world, that is, around the
Sun itself.
So this is Jupiter orbiting around the Sun on a relatively long time scale.
Same time, the moons are orbiting around Jupiter.