Galileo's Dream (6 page)

“Idiots that they are!” Galileo shouted but did not add to the end of the letter, signing it conventionally and sending it off.

Naturally Sarpi did not forward this letter to the senate, but rather came out to Padua to assuage his angry friend. “I know,” he said apologetically, putting his hand to Galileo's freckled cheek, now as red as his hair as he recounted the reasons for his fury. “It isn't fair.”

And it was even less fair than Galileo thought, for Sarpi now told him that the senate had decided that the stipulated raise in Galileo's salary was not to go into effect immediately after all, but would begin the following January.

At this Galileo blew up again. And after Sarpi left, he immediately took action to deal with the insults, working in two directions. In Venice, he returned to the city with a much more powerful spyglass, the best his artisans had made so far, and gave it to the doge as a present, indicating again how useful it would be to the protection of the republic, how grateful he was for the new contract, how much the splendiferousness of the doge illuminated not just the Serenissima but the entire watershed of the Po, et cetera. Dona would take note of this generosity, perhaps, in the face of what could be seen as a very tepid response from his senate. And then maybe he would act to revise the raise accordingly. It was not the likeliest response, but it could happen.

Then, on the Florentine front—always a part of his life, even in these last seventeen years in Padua working for Venice—Galileo wrote to young Grand Duke Cosimo's secretary Belisario Vinta, telling him about the spyglass, offering to give the prince one of them and to instruct him in its use. A few of the closing phrases of this letter began the process of asking for patronage at the Medici court.

There were some difficulties to be negotiated here. Galileo had been tutor to young Cosimo when his father Ferdinando was the grand duke, and that was good. But he had also been asked to work up a horoscope for Ferdinando the previous year, and had done so, and found that the stars predicted a long and healthy life for the grand duke, in the usual way. But then, shortly thereafter, Ferdinando had died. That was bad. In the tumult of the funeral and the succession no one had said anything, nor even seemed to remember the horoscope, except for a single penetrating glance from Vinta the next time they met. So perhaps in the end it had not mattered. And Galileo had taught Cosimo his mathematics, and treated him very kindly, of course, so that they had grown fond of each other. Cosimo was a bright young man, and Cosimo's mother, the Grand Duchess Christina,
was a very intelligent woman, and fond of Galileo—indeed, his true first patron at that court. And as Cosimo was so young, and new to his rule, she was a regentlike power. So the possibilities there were very real. And when all was said and done, Galileo was a Florentine; it was his home. His family was still there, which was bad, but unavoidable.

So, still very angry at the Venetians for their ingratitude, he neglected his classes at Padua, wrote great flurries of letters to influential friends, and began to lay plans to move.

During this time, despite the discord and chaos of the tumble of days, he spent every cloudless night out in the garden, looking through the best glass they had on hand. One night he woke Mazzoleni and took him out to look at the moon. The old man peered up through the tube and then pulled his head back, grinning, shaking his head in amazement. “What does it mean?”

“It's a world, like this one.”

“Are there people there?”

“How should I know?”

When the moon was up, and not too full, Galileo looked at it. Long ago he had taken drawing lessons from his Florentine friend Ostilio Ricci, the better to be able to sketch his mechanical ideas. One of the exercises in Ricci's treatise on perspectival drawing had been to draw spheres studded with geometrical figures, like raised pyramids or cubes, each one of which had to be drawn slightly differently to indicate where they stood on the hidden surface of the sphere beneath them. This was a meticulous and painstaking form of practice, very
polito
, at which Ricci had conceded Galileo eventually became the superior. Now Galileo found that it had given him the necessary skills, not just to draw the things the glass showed on the moon, but even to see them in the first place.

It was particularly revealing to draw the moon's terminator, where light and shadow mixed in patterns that changed from night to night. As he wrote in his workbook:
With the moon in various aspects to the sun, some peaks within the dark part of the moon appear drenched in light, although very far from the boundary line of the light and darkness. Comparing
their distance from that boundary line to the entire lunar diameter, I found that this interval sometimes exceeds the twentieth part of the diameter
.

The moon's diameter had been proposed since antiquity to be about two thousand miles; thus he had enough to complete a simple geometrical calculation of the height of these lunar mountains. He drew the moon as a circle, then on it drew a triangle with one side the radius at the terminator, another a radius running up to the tip of the lit mountain in the dark zone, and the third line following the beam of sunlight from the terminator to the mountaintop. The two sides meeting at the terminator would be at right angles, and he had distances for both, based on the assumed diameter, and thus he could use the Pythagorean theorem to calculate the length of the hypotenuse. Subtracting the moon's radius from that hypotenuse, one was left with about four miles of difference—which was the height of the mountain above the surface at the terminator.

But on Earth
, he wrote
, no mountains exist that reach even to a perpendicular height of one mile
. The mountains on the moon were taller than the Alps!

One night when the moon was in its last quarter, he spotted a perfectly round crater, right in the middle of the terminator, and very near the equator. He drew it a bit bigger than he saw it, to emphasize how prominent it was to the eye, and how clearly it stood out from its surroundings. A good astronomical drawing, he decided, had to evoke the sight that subsequent viewers would look for, rather than represent it to perfect scale, which in the diminution of the drawing simply made it
too
small. Paying attention was itself a kind of magnification.

Drawing the constellations with their new host of companion stars was a different kind of problem, easier in some ways, as being mostly a schematic, but much harder too, in that there was no chance of representing what the view through the glass actually looked like. He altered sizes far beyond what he saw, to give an impression of the different brightnesses, but using black on white to represent white on black would never be satisfactory. White marks on black, as in an etching, would be better.

He drew till his fingers got too cold. He made fair copies in the mornings, exaggerating to make the impressions bolder than ever. He
made ink washes, very delicate; also bold schematics that would serve as guides to an engraver, because already he had plans for a book to accompany the spyglasses, just as an instruction manual had accompanied his military compass. Although here it really came down to seeing for one's self. The Milky Way, for instance; he could see that it was composed of a vast number of stars granulated together. A truly astonishing finding, but there was no way at all to draw it. People would have to see for themselves.

As November wore on, and the nights got colder, he fell deeply into his new routine. He had always been an insomniac, and now there was a useful way to spend those sleepless hours. He simply did not go to bed, but stayed out on the terrace by the occhialino, looking through it and jotting down notes, comfortable in the solitary silence of the sleeping town. He had not known how much he enjoyed being alone. He wrote up what he had observed at dawn, and then slept through many a bright cool morning, wrapped in a blanket against a sunny wall in the corner, under the gnomon of the house's big L.

With the shorter days of December came winter, and clouds. On those nights he read, or caught up on his sleep, if he could. But on many a night he woke every hour or two, his brain full of stars, and went out to check the sky. If it had cleared, he would stir the coals of the kitchen fire and put a pot of mulled wine on the grate, add a few sticks and go out to set up the glass, feeling that swirl of dust in the blood that he loved so much. He was on the hunt all right, and never had he had such a quarry! Nothing could keep him from looking when the night was clear. If his day work had to suffer—and it did—so be it. Those bastard
pregadi
didn't deserve his work anyway.

He had ordered one of the worktables moved onto the terrace next to the garden, and placed under a table umbrella next to a couch. He had a lantern that could be shuttered, and workbooks, inkpots, and quills; and three spyglasses on tripods, each with different strengths and occlusions. Lastly, blankets to throw over his shoulders. Mazzoleni and the cook kept things running in the mornings while he slept, and stocked the supplies for his nighttime needs; both were the kind of person who falls asleep at sunset, so they didn't see him at work unless he forced them to. After a while, he never did. He liked
being by himself through the frosty nights, looking at first one thing and then another.

On the night of January 7, 1610, he was out looking at the planets. As he had written in a letter he was composing for young Antonio Medici:
The planets are seen very rotund, like little full moons, and of a roundness bounded and without rays. But the fixed stars do not appear so; rather they are seen fulgurous and trembling, much more with the glass than without, and so irradiated that what shape they possess is not revealed
.

So the planets, being obvious little disks, were interesting. And Jupiter was now in the west after sunset. It was the biggest of the planets in the glass—no surprise to anyone used to the way it dominated the night sky whenever it was visible.

Galileo got it in the middle of the eyepiece, and then saw that there were three bright stars to left and right of it, aligned with it in the plane of the ecliptic. He marked their position on a new sheet of his letter to Antonio, and looked at them for a long time. They did not twinkle like the stars, but gleamed steadily. They were almost perfectly on a line with each other. They were almost as bright as Jupiter, or even brighter, although smaller. Jupiter itself was a very distinct disk.

The next night he looked at Jupiter again, and was shocked to find that the three stars were still there, but this time all to the west of the great planet, whereas on the previous night two of them had been to its east. He wondered if the ephemerides for the night was wrong.

On January 9 it was cloudy, and nothing could be seen. But the night of January 10 was clear again.

This time only two of the bright stars were there, both to the east of Jupiter. One was slightly less bright than the other, though on the previous nights they had all been the same.

Mystified—intrigued to the point of obsession—Galileo started a new sheet in his workbook, and copied there the diagrams he had already written in at the end of the letter to Antonio. The letter itself he put aside, as being premature.

In his new desire for night, the days themselves passed slowly, and he did the necessary work without paying the slightest attention to it, as if dreaming on his feet. This was a sign, well-recognized by the
household: he was on the hunt. And just as they never woke sleepwalkers for fear of damaging their sanity, they left him alone at these times, and kept the boys quiet and the students at bay, and put food in him almost as if spoon-feeding a baby. Of course, it was true he would beat them if they distracted him, but they enjoyed the craft of it too.

On the night of January 12, Galileo trained the glass on Jupiter in the last moments of twilight. At first he could see again only two of the little bright stars, but an hour later, when it was fully dark, he checked again, and one more had become visible, very close to Jupiter's eastern side.

He drew arrows trying to clarify to himself how they were moving, shifting his attention between the view through the glass and his sketches on the page. Suddenly it became clear, there in the reiterated sketches: the four stars were moving around Jupiter, orbiting it in the same way the moon orbited the Earth. He was seeing circular orbits edge-on; they lay nearly in a single plane, which was also very close to the plane of the ecliptic, in which the planets themselves moved.

He straightened up, blinking away the tears in his eyes that always came from looking too long, and that this time came also from the sudden surge of an emotion he couldn't give a name to, a kind of joy that was also shot with fear. “Ah,” he said. A touch of the sacred, right on the back of his neck: God had tapped him. He was ringing.

No one had ever seen this before. People had seen the moon, had seen the stars; they had
never
seen this.
I primi al mondo!
The first man to see Jupiter's four moons, which had been circling it since the creation.

Everything he had seen over the last week fell into place. He stood, staggering a little under the impact of the idea, and circled the work-table as if imitating a moon. When there had been only two dots, the others could have been behind the big planet—or before it. And he saw also that the orbiting moon now outermost could perhaps have moved so far away from Jupiter as to be outside his eyepiece's little circle. The shifts in position suggested they were moving fairly quickly. Earth's moon took only twenty-eight and a half days for its orbit. These four seemed faster, and perhaps could be moving at differing speeds, just as the planets moved at differing speeds in the sky.

If he were right, then he could expect to see several more things. Seeing the orbits side-on, the moons would appear to slow down as
they approached their maximum distance from Jupiter, and be fastest when right next to it. They would also disappear when behind it (or before it) in a regular pattern, and always reappear on the other side, never on the same side. Repeated observations should make it possible to sort out which moon was which, and determine which orbited closest to Jupiter and which farthest away. Knowing that would help him to calculate each orbital period, and that would allow him to keep steady track of them, and even predict where they would be, in a Jovian ephemerides of his own device.