Philosophy 167: Class 5 - Part 4 - Sidereus Nuncius: the Discovery of the Galilean Moons, and the Lunar Topography.

Smith, George E. (George Edwin), 1938-


  • Synopsis: Discusses Siderius Nuncius, in which Galileo published his discovery of the four largest moons of Jupiter and his telescopic survey of the surface of the moon.

    Opening line: "So that's the original title page of Sidereus Nuncius."

    Duration: 8:59 minutes.

    Segment: Class 5, Part 4.
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So that's the original title page of Sidereus Nuncius. And notice what the largest words on the whole page are besides Sidereus, namely the Medicean stars. He's named the four Kepler's words, Satellites of Jupiter, he called them four new stars. But the four stars orbiting Jupiter, he proposed to name after the Grand Duke's children, of course that's one way to endure yourself.
When you read the preface that's an understatement, because what he says is, in the past they have always done it after Greek Gods but surely you Cosimo are at least as glorious as the Greek Gods. Therefore it is appropriate etc, to name it after you. I'm paraphrasing, but some of you have read it recently.
I'm not doing that much injustice to it. And you notice, singles out the four planets, I'm giving it to you in English now. And I'll pass it around. This is a new book just put out, Library of Congress paid for it. What's nice about it is it contains a full facsimile done off of camera of a first edition.
That's the reason I have it, cuz I didn't have a first edition, even in facsimile. And it has the Van Helden translation in the back, which is really the best translation. I didn't give it to you simply. That's this translation. I didn't give it to you because I wanted you to have the Drake discoveries and opinions cause there are so many other wonderful things in it.
But I'll pass this around and you can all look, and this is just taken out of that. So let's look at it. Sidereal messenger unfolding great and very wonderful sights and displaying to the gaze of everyone, but especially philosophers and astronomers, the things that were observed by Galileo Galilei, Florentine patrician, and public mathematician of the University of Padua.
With the help of a spy glass, lately devised by him about the face of the moon, countless fixed stars, the Milky Way, nebulous stars, but especially about four planets flying around the star of Jupiter at unequal intervals. And periods with wonderful swiftness, which unknown by anyone until this day, the first author detected recently and decided to name Medicean stars.
Okay, nice title page, and all you're getting is the English corresponding to the Latin. I'm gonna come back and look at these a little further, these discoveries, but I simply wanna show you some slides from it. These are lifted off the facsimile pages. So this is the moon.
You will notice that, I assume these are wood cuts, but you can see that the printing of the figure has to be separate from the printing of the pages. They're done separately. It was fairly unusual at the time to have books where the figures are within the pages.
They're normally put on separate pages at the end. So this is a substantial further expense doing it this way. It's also true of Newton's Principia, but things were fairly different 80 years later in terms of the technology of printing, etc. So it probably wasn't so bad. But they're carefully drawn.
The spectacular thing about this, and with this light shining down I don't know how well you can see. But, look at the crater, look at the extent of the shadow and then the lightness where the sun manages to reach part of the crater. That's a very long shadow, that crater is very deep.
So he started figuring out how deep these things were, how high the mountains were from their shadows, and he got a very accurate number. The mountains are about four miles high. He then said nothing that high on Earth, and that's a comment about how much he knew about mountains on Earth in Europe at that time, nothing more.
But the point is, and of course the shock here was this is a celestial object that's supposed to be perfect. Aristotle told us it was perfect. It looks just like the bloody Earth except more so, therefore there's no difference between the Earth and the moon. Celestial objects are not of a different kind.
That's the sort of point that was being made. And he goes on at some length about the moon. The next one I'm showing you is one page I now regret not having done two pages on this and showing you the two. Of his drawings, page after page of these, of the four planets going around Jupiter.
Notice he doesn't, in these drawings, detect the belt across Jupiter. He probably didn't have enough power to actually see the belt clearly, but he did pick up the four stars. Until you see them, until you go out, look up at Jupiter, see none of them, look through a telescope, even good binoculars, and see them.
The shock of seeing them. You can't appreciate it. That's one of the things that I regret. Jupiter is not visible this fall, so we can't see it til spring for me to show you this. But I can tell it anecdotally with my daughter. So, she was eight years old when we got the telescope in my office for her.
She picked it, I've already told this story, she picked it out at the Science Museum and it turned out to cost $500. I called a professor here at Tufts, and his comment was she has good taste, buy it. So, I took his word for it. But when we assembled it and the first thing she wanted to see was Jupiter and she just sort of screamed out exactly the way he drew it.
Which is basically right and I showed it to you earlier, you see those four stars sort of in line with one another on the sides. He did not work out the periods on these at the time of Sidereus Nuncius. They are, and I don't, I have to look at this, 1.769 days for IO, the innermost.
3.551 days for Europa, the second. Ganymede is 7.155 days, and Callisto is 16.689 days. So the longest is 16 days, the shortest is less than two days, period. I've had at least one student actually see one go into eclipse while looking through the telescope. All you have to do is look a while and you will see them go into eclipses, and that became a big deal, partly because Galileo used it.
It provides a way to get a simultaneous event in two places on the Earth. And if you have local clocks in the two places, you have the longitudinal difference between them for purposes of mapping. Galileo's the one who proposed that, but he couldn't get good enough behavior of the satellites to use it.
Okay, that will come later. I gave you their present names, the Medicean names did not stick. It turns out one Simon, Simone Maher, Latin, Marius, probably saw these four before Galileo. At least his notebooks indicate he was before Galileo. He didn't need patronage, so he didn't rush to print.
He instead did several months of very careful study of them, getting their orbits and their periods very, very precisely. And he named them and his name it stuck. Maher had worked with Tycho in 1601 when Kepler first joined him, so Kepler knew him personally. And Kepler backed him on both the names and the priority for what it's worth.
One of the many things that interfered with Kepler and Galileo having good relations, as you'll see in a few minutes. At any rate, there's an attitude here among professional astronomers, and you'll see why when we get to the dialog on two-world systems, that Galileo wasn't really an astronomer.
Okay. He was somebody looking through a telescope, and that was wonderful and he did an enormous amount to popularize it. But he wasn't the sort of person who would take the trouble that any mathematical astronomer were to work out really detailed orbits, and figure out eccentricities, all those things.
And Maher did, Maher was part of the community, so his name stuck. Galileo's did not. Whether anything else was involved, I don't know.