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 centre. 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 the age of 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-centred 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 alternative 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 was likely to hold 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 suddenly to materialise. 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 honoured 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 honourable 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 favour 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
