fulfilling that intention until now, when he could also offer thanks for his recent recovery and pray for improved health in the future.
He returned home in June to Bellosguardo and to his son, Vincenzio, whom he had brought from Padua in 1612 at the age of seven. By 1618, their male-dominated household also included two new students, Mario Guiducci and Niccolo Arrighetti, who, like Castelli before them and others to come after, would remain Galileo’s devoted friends for life. The thirtyish scholars busied themselves all that summer copying the master’s early theorems on motion, to help him return to the fundamental work he had forsaken in 1609 for the telescope. They mined the dense jumble of his Paduan notes and prepared neat sheets of paper, written extravagantly on one side only, for his review and revision.
The three comets of 1618
In September, just when Galileo’s student assistants had finished this preliminary work, another bout of illness prevented him from building on it as planned. The delay might have been merely temporary, except that while Galileo languished, the heavens sent him a new mystery to ponder, and this apparition initiated a cascade of events that postponed the publication of his motion studies for another two decades.
A small comet glowed in the skies over Florence that September of 1618. Though unspectacular, as comets go, it was nevertheless the first comet to appear since the birth of the telescope. Other astronomers took to their rooftops with instruments of Galileo’s design, but Galileo himself remained indoors an invalid. Then another comet arrived in mid-November, while Galileo unfortunately fared no better than before. And even by the end of November, when a truly brilliant third comet burst on the scene to garner the attention of observers all over Europe, Galileo still could not stand among them.
“During the entire time the comet was visible,” he reported later, “I was confined by illness to my bed. There I was often visited by friends. Discussions of the comets frequently occurred, during which I had occasion to voice some thoughts of mine which cast doubt upon the doctrines that have been previously held on this matter.” In fact, Galileo saw only one important comet his whole life—the big bright one of 1577, in his youth—and never did figure out what these objects really were.
Most of Galileo’s contemporaries feared comets as evil omens. (Indeed the three 1618 examples were presently seen, with hindsight, as heralds of the Thirty Years’ War, which broke out in Bohemia the same year.) Aristotelian philosophers figured comets for atmospheric disturbances. The fact that comets came and went, changing their fuzzy-glow appearance all the while, automatically relegated them to the sublunar sphere between the Earth and the Moon, where they were thought to be ignited by friction of the sphere’s turning against the upper reaches of the air.
It may seem incredible that Galileo resisted the temptation to go outdoors in the autumn of 1618 long enough to view any one of the three comets, especially since he felt well enough to enter into intellectual discussions with visitors. But in fact the November night air held terrible danger for him, a man well past fifty now, who had spent most of the current year battling one malady after another. Moreover, as Galileo no doubt knew from his friends’ accounts, he would not have seen much even if he had risked his own study of these objects. A comet, or “hairy star,” retained its blurred contours despite the aid of the most powerful telescope * Unlike the fixed stars that resolved into points of light when the telescope stripped them of their rays, or planets that turned to tiny globes, a comet could not be brought into sharp focus. And Galileo held back because he believed—in agreement for once with his Aristotelian contemporaries, though not for the same reasons—that comets belonged to the Earth’s
He returned home in June to Bellosguardo and to his son, Vincenzio, whom he had brought from Padua in 1612 at the age of seven. By 1618, their male-dominated household also included two new students, Mario Guiducci and Niccolo Arrighetti, who, like Castelli before them and others to come after, would remain Galileo’s devoted friends for life. The thirtyish scholars busied themselves all that summer copying the master’s early theorems on motion, to help him return to the fundamental work he had forsaken in 1609 for the telescope. They mined the dense jumble of his Paduan notes and prepared neat sheets of paper, written extravagantly on one side only, for his review and revision.
The three comets of 1618
In September, just when Galileo’s student assistants had finished this preliminary work, another bout of illness prevented him from building on it as planned. The delay might have been merely temporary, except that while Galileo languished, the heavens sent him a new mystery to ponder, and this apparition initiated a cascade of events that postponed the publication of his motion studies for another two decades.
A small comet glowed in the skies over Florence that September of 1618. Though unspectacular, as comets go, it was nevertheless the first comet to appear since the birth of the telescope. Other astronomers took to their rooftops with instruments of Galileo’s design, but Galileo himself remained indoors an invalid. Then another comet arrived in mid-November, while Galileo unfortunately fared no better than before. And even by the end of November, when a truly brilliant third comet burst on the scene to garner the attention of observers all over Europe, Galileo still could not stand among them.
“During the entire time the comet was visible,” he reported later, “I was confined by illness to my bed. There I was often visited by friends. Discussions of the comets frequently occurred, during which I had occasion to voice some thoughts of mine which cast doubt upon the doctrines that have been previously held on this matter.” In fact, Galileo saw only one important comet his whole life—the big bright one of 1577, in his youth—and never did figure out what these objects really were.
Most of Galileo’s contemporaries feared comets as evil omens. (Indeed the three 1618 examples were presently seen, with hindsight, as heralds of the Thirty Years’ War, which broke out in Bohemia the same year.) Aristotelian philosophers figured comets for atmospheric disturbances. The fact that comets came and went, changing their fuzzy-glow appearance all the while, automatically relegated them to the sublunar sphere between the Earth and the Moon, where they were thought to be ignited by friction of the sphere’s turning against the upper reaches of the air.
It may seem incredible that Galileo resisted the temptation to go outdoors in the autumn of 1618 long enough to view any one of the three comets, especially since he felt well enough to enter into intellectual discussions with visitors. But in fact the November night air held terrible danger for him, a man well past fifty now, who had spent most of the current year battling one malady after another. Moreover, as Galileo no doubt knew from his friends’ accounts, he would not have seen much even if he had risked his own study of these objects. A comet, or “hairy star,” retained its blurred contours despite the aid of the most powerful telescope * Unlike the fixed stars that resolved into points of light when the telescope stripped them of their rays, or planets that turned to tiny globes, a comet could not be brought into sharp focus. And Galileo held back because he believed—in agreement for once with his Aristotelian contemporaries, though not for the same reasons—that comets belonged to the Earth’s
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