Galileo's Daughter (8 page)

In 1543, however, the Polish cleric Nicolaus Copernicus flung the Earth from its central position into orbit about the Sun, in his book
On the Revolutions of the Heavenly Spheres,
or
De revolutionibus,
as it is usually called. By imagining the Earth to turn on its own axis once a day, and travel around the Sun once a year, Copernicus rationalized the motions of the heavens. He saved the enormous Sun the trouble of traipsing all the way around the smaller Earth from morning till evening. Likewise the vast distant realm of the stars could now lie still, instead of having to wheel overhead even more rapidly than the Sun every single day. Copernicus also called the planets to order, relieving those bodies of the need to coordinate their relatively slow motion toward the east over long periods of time (Jupiter takes twelve years to traverse the twelve constellations of the zodiac, Saturn thirty) with their speedy westward day trips around the Earth. Copernicus could even explain the way Mars, for example, occasionally reversed its course, drifting
backward
(westward) against the background of the stars for months at a time, as the logical consequence of heliocentrism: The Earth occupied an inside track among the paths of the planets—third from the Sun, as opposed to Mars’s fourth position—and could thus overtake the slower, more distant Mars every couple of years.

Copernicus, who studied astronomy and mathematics at the University of Cracow, medicine for a while in Padua, and canon law in Bologna and Ferrara, devoted most of his life to cosmology, thanks to nepotism. When he returned to Poland from his studies in Italy at age thirty, his uncle, a bishop, helped secure Copernicus a lifetime appointment as a canon at the cathedral of Frombork. Serving forty years in that “most remote corner of the Earth,” with manageable duties and a comfortable pension, Copernicus created an alternate universe.

“For a long time I reflected on the confusion in the astronomical traditions concerning the derivation of the motion of the spheres of the Universe,” Copernicus wrote in Frombork. “I began to be annoyed that the philosophers had discovered no sure scheme for the movements of the machinery of the world, created for our sake by the best and most systematic Artist of all. Therefore, I began to consider the mobility of the Earth and even though the idea seemed absurd, nevertheless I knew that others before me had been granted the freedom to imagine any circles whatsoever for explaining the heavenly phenomena.”

Although he made numerous naked-eye observations of the positions of the planets, most of Copernicus’s lonely work involved reading, thinking, and mathematical calculations. He proffered no supporting evidence of any kind. And nowhere, alas, did he record the train of thought that led him to his revolutionary hypothesis.

An anonymous introductory note to Copernicus’s book dismissed the whole conceit as merely an aid to computation. The complex business of determining the orbital periods of the planets, including the Sun and Moon, figured crucially in establishing the length of the year and the date of Easter. Copernicus himself, writing in the languages of Latin and mathematics for a scholarly audience, never attempted to convince the general public that the universe was actually constructed with the Sun at the center. And who would have believed him if he had? The fact that the Earth remained motionless was a truism, obvious to any sentient individual. If the Earth rotated and revolved, then a ball tossed into the air would not fall right back into one’s hands but land hundreds of feet away, birds in flight might lose the way to their nests, and all humanity suffer dizzy spells from the daily spinning of the global carousel at one thousand miles per hour.
*

“The scorn which I had to fear,” Copernicus remarked in
De
revolutionibus,
“on account of the newness and absurdity of my opinion almost drove me to abandon a work already undertaken.” Continuous calculation and checking delayed publication of his manuscript for decades, until he lay literally on his deathbed. Expiring at age seventy, immediately after the first printing of his book in 1543, Copernicus avoided any brush with derision.

When Galileo ascended the wooden steps of his teaching platform at Padua to lecture on planetary astronomy, beginning in 1592, he taught the Earth-centered view, as it had been preserved from antiquity. Galileo knew of Copernicus’s challenge to both Aristotle and Ptolemy, and he may have casually mentioned this alternate idea to his students, too. Heliocentrism, however, played no part in his formal curriculum, which was primarily concerned with teaching medical students how to cast horoscopes. Nevertheless, Galileo gradually convinced himself that the Copernican system not only looked neater on paper but very likely held true in fact. In a 1597 letter he wrote to a former colleague at Pisa, Galileo assessed the system of Copernicus as “much more probable than that other view of Aristotle and Ptolemy.” He expressed the same faith in Copernicus in a letter he wrote to Kepler later that year, regretting how “our teacher Copernicus, who though he will be of immortal fame to some, is yet by an infinite number (for such is the multitude of fools) laughed at and rejected.” Since the Copernican system remained just as absurd to popular opinion fifty years following its author’s demise, Galileo long maintained his public silence on the subject.

In 1604, five years prior to Galileo’s development of the telescope, the world beheld a never-before-seen star in the heavens. It was called “nova” for its newness.
*
It flared up near the constellation Sagittarius in October and stayed so prominent through November that Galileo had time to deliver three public lectures about the newcomer before it faded from bright view. The nova challenged the law of immutability in the heavens, a cherished tenet of the Aristotelian world order. Earthly matter, according to ancient Greek philosophy, contained four base elements—earth, water, air, fire—that underwent constant change, while the heavens, as Aristotle described them, consisted entirely of a fifth element—the quintessence, or aether—that remained incorruptible. It was thus impossible for a new star to suddenly materialize. The nova, the Aristotelians argued, must inhabit the sublunar sphere between the Earth and the Moon, where change was permissible. But Galileo could see by comparing his nightly observations with those of other stargazers in distant lands that the new star lay far out, beyond the Moon, beyond the planets, among the domain of the old stars.

In his playful, provocative way, Galileo presented the nova controversy to the public in a dialogue between a pair of peasants speaking Paduan dialect, which he published under the pen name Alimberto Mauri. Call the new star “quintessence,” his gruff hero concluded, or call it “polenta!” Careful observers could measure its distance just the same.

Having thus impugned the immutability of the heavens, Galileo further attacked the defensive Aristotelian philosophers by turning the telescope on their territory in 1609. His telescopic discoveries transformed the nature of the Copernican question from an intellectual engagement into a debate that might be decided on the basis of evidence. The roughness of the Moon, for example, showed that some of the features of Earth repeated themselves in the heavens. The motions of the Medicean stars demonstrated that satellites could orbit bodies other than the Earth. The phases of Venus argued that at least one planet must travel around the Sun. And the dark spots discovered on the Sun sullied the perfection of yet another heavenly sphere. “In that part of the sky which deserves to be considered the most pure and serene of all—I mean in the very face of the sun,” Galileo reported, “these innumerable multitudes of dense, obscure, and foggy materials are discovered to be produced and dissolved continually in brief periods.”

Galileo rued the stubbornness of philosophers who clung to Aristotle’s views despite the new perspective provided by the telescope. He swore that if Aristotle himself were brought back to life and shown the sights now seen, the great philosopher would quickly alter his opinion, as he had always honored the evidence of his senses. Galileo chided the followers of Aristotle for being too timid to stray from their master’s texts: “They wish never to raise their eyes from those pages—as if this great book of the universe had been written to be read by nobody but Aristotle, and his eyes had been destined to see for all posterity.”

Several of Galileo’s Aristotelian opponents sputtered that the sunspots must be a new fleet of “stars” circling the Sun the way the Medicean stars orbited Jupiter. Even professors who had vociferously rejected the moons of Jupiter, damning them as demonic visions spawned by the distorting lenses of Galileo’s telescope, now turned to embrace them as the Sun’s last hope for maintaining its steady stateliness.

One of the first scientists to see sunspots, Galileo gathered important correspondents among foreign astronomers seeking to compare observations and interpretations with him. In January of 1612, while still convalescing at the Villa delle Selve outside Florence, Galileo heard much about sunspots from a German gentleman and amateur scientist named Marcus Welser. “Most Illustrious and Excellent Sir,” Welser hailed Galileo,

Already the minds of men are assailing the heavens, and gain strength with every acquisition. You have led in scaling the walls, and have brought back the awarded crown. Now others follow your lead with the greater courage, knowing that once you have broken the ice for them it would indeed be base not to press so happy and honorable an undertaking. See, then, what has arrived from a friend of mine; and if it does not come to you as anything really new, as I suppose, nevertheless I hope you will be pleased to see that on this side of the mountains also men are not lacking who travel in your footsteps. With respect to these solar spots, please do me the favor of telling me frankly your opinion—whether you judge them to be made of starry matter or not; where you believe them to be situated, and what their motion is.

Enclosed Galileo found several essays by Welser’s “friend,” an anonymous astronomer (later revealed as Father Christopher Scheiner, Jesuit professor at the University of Ingolstadt), who tried to explain the new phenomenon according to the old philosophy, protecting his identity behind the pseudonym “Apelles.”

Galileo took nearly four months to formulate his reply, constrained at first by his illness (“a long indisposition,” he called it, “or I should say a series of long indispositions preventing all exercises and occupations on my part”), and even further by the calumny of his enemies, not to mention the mysterious nature of the spots themselves.

“The difficulty of this matter,” Galileo finally conceded to Welser, “combined with my inability to make many continued observations, has kept (and still keeps) my judgment in suspense. And I, indeed, must be more cautious and circumspect than most other people in pronouncing upon anything new. As Your Excellency well knows, certain recent discoveries that depart from common and popular opinions have been noisily denied and impugned, obliging me to hide in silence every new idea of mine until I have more than proved it.” Nonetheless, Galileo expounded on the essence and substance of sunspots for many pages, initiating an ongoing correspondence with Welser—and through him “the masked Apelles”—that sounded the full thunder of the new debate. Indeed, Galileo’s letters on sunspots speak almost as much about the system of the world as they do about the solar spots.

“With absolute necessity we shall conclude,” Galileo wrote early in the first of his three letters to Welser, “in agreement with the theories of the Pythagoreans and of Copernicus, that Venus revolves about the Sun just as do all the other planets. . . . No longer need we employ arguments that allow any answer, however feeble, from persons whose philosophy is badly upset by this new arrangement of the universe.”

Apelles upheld the idea that the dark spots must be many small stars circling the Sun. Galileo saw nothing starlike about them. To his mind, they more closely resembled clouds: “Sunspots are generated and decay in longer and shorter periods; some condense and others greatly expand from day to day; they change their shapes, and some of these are most irregular; here their obscurity is greater and there less. They must be simply enormous in bulk, being either on the Sun or very close to it. By their uneven opacity they are capable of impeding the sunlight in differing degrees; and sometimes many spots are produced, sometimes few, sometimes none at all.”

But he quickly added: “I do not assert on this account that the spots are clouds of the same material as ours, or aqueous vapors raised from the Earth and attracted by the Sun. I merely say that we have no knowledge of anything that more closely resembles them. Let them be vapors or exhalations then, or clouds, or fumes sent out from the Sun’s globe or attracted there from other places; I do not decide on this—and they may be any of a thousand other things not perceived by us.” (He could never have imagined, despite his long-standing interest in magnets, that the spots marked the sites of the Sun’s most potent magnetic fields.)

“If I may give my own opinion to a friend and patron,” Galileo continued, “I shall say that the solar spots are produced and dissolve upon the surface of the Sun and are contiguous to it, while the Sun, rotating upon its axis in about one lunar month, carries them along, perhaps bringing back some of those that are of longer duration than a month, but so changed in shape and pattern that it is not easy for us to recognize them.”

In closing this first letter, Galileo begged Welser’s indulgence:

And forgive me my indecision, because of the novelty and difficulty of the subject, in which various thoughts have passed through my mind and met now with assent and again with rejection, leaving me abashed and perplexed, for I do not like to open my mouth without declaring anything whatever. Nevertheless, I shall not abandon the task in despair. Indeed, I hope that this new thing will turn out to be of admirable service in tuning for me some reed in this great discordant organ of our philosophy—an instrument on which I think I see many organists wearing themselves out trying vainly to get the whole thing into perfect harmony. Vainly, because they leave (or rather preserve) three or four of the principal reeds in discord, making it quite impossible for the others to respond in perfect tune.