Biographies such as NOVA's Galileo's Battle for the Heavens commonly portray Galileo relationship with his contemporaries as a lone star in an otherwise dark sky. Discounting Galileo's contemporaries distorts the discussion of both church and science. Galileo had many important contemporaries including Kepler, Descartes, Pascal, Gassendi and Mersenne . A timeline of science contemporary with Galileo is found at Galileo's Contemporaries. After Galileo's death, when Newton took science the next giant step forward, it was Kepler's work that he used as the anchor for his greatest work (the Principia Mathematica). Newton's philosophy of science was also more influenced by the priest-scientist Gassendi than by Galileo. Galilean biographies rarely mention Kepler. In the case of Galileo's Battle for the Heavens this distortion reached extremes. Like many Galileo discussions, it presents Giordano Bruno as an important scientific figure, mentioning him 7 times, and completely discounts Kepler's contributions, not mentioning him once. Bruno did not contribute a single advance in fact or theory to the science of the day.
Early in Galileo's Battle for the Heavens we are warned that what we were about to see was another example of the "recurring clash between religion and science". Developing this premise was helped by ignoring Kepler and his relations with the Church. Although the Church never provided Kepler with ongoing research grants as they had Galileo [_1_] , they did provide something more important; access to resources and moral support. When Galileo ignored an early request from Kepler to borrow a telescope, it was the Archbishop of Cologne who leant him one. The last of Kepler's books to be published, Somnium, contained a gushing thank you to the Jesuit mathematician, Paul Guldin, an enduring advocate and friend of Kepler. The appendix also mentioned his joy over the gift of a telescope hand-made by the master Jesuit telescope-maker, Niccolo Zucchi. Between these early and later events there were many other events, including the Jesuits chasing down a manuscript stolen from Kepler and ensuring its return, and the Jesuits acting as a surrogate postal service for Kepler.
When modern biographies ignore Galileo's contemporaries it doesn't mean that scientists of the time did. The scientists of the day, including church scientists, were following Galileo's work, but also Kepler's. The priest-scientist Gassendi was a follower of Galileo's work. He conducted several of the experiments Galileo described in his books. But he was also a follower of Kepler. Kepler's model predicted that Mercury should pass between the earth and the sun (known as a Transit of Mercury) on November 7, 1631. The scientists of Europe were well-warned of this event in publications by Kepler and his assistant. Gassendi also published a pamphlet reminding interested scientists of this event. This was a watershed event; the first international experiment. The transit of Mercury was detected by Gassendi in Paris and other observers in Alsace, Austria, and Bavaria (see Gassendi's Transit of Mercury). Scientists around Europe, including Galileo, would have known of the experiment. Although the discovery by Gassendi that Mercury was much smaller than expected helped some of Galileo's arguments, this remarkable experiment gave credence to a model that competed with Galileo's own model; one that assumed elliptical orbits. It is Kepler's model that is taught in schools today. All this happened more than a year before Galileo's famous trial.
But Kepler was not the only contemporary of Galileo who was developing models to compete with the old Ptolemaic model. There were at least 6 models being proposed. The program, like so many other biographies of Galileo, builds a straw man, by suggesting that the choices were between Galileo's Copernican model and an archaic model inherited from Aristotle. Another important scientist of the day, Tycho Brahe, had developed the Tychonic System. The Jesuits mentioned in the program (e.g Scheiner) were not proponents of the old Ptolemaic system but of the newer Tychonic System. They were not clutching to some ancient model. The Tychonic system had been published in 1587, more than 40 years after Copernicus' death. It was based on the best set of celestial data up to that time. The data set was eventually used by Kepler to propose our modern view of planetary motion. A measure of Kepler's and Brahe's importance is Newton's high regard for their work. The image below is a word cloud (see wordle.net) of references to scientists in Newton's great work,Philosophiæ Naturalis Principia Mathematica . References in the book's preface were not included.
Tycho Brahe's model was a hybrid system, where the sun circled the earth but the other planets circled the sun. The program describes important experiments where Galileo discovers that Venus actually revolves around the sun and not the earth. Galileo took this as proof of the Copernican model. But this behavior was completely consistent with the Tychonic model as well. This fact was lost on the viewers, since neither Tycho Brahe nor the Tychonic system were ever mentioned in the program. The Tychonic system has a significance beyond the controversies on planetary motion in the seventeenth century. One has to ask why Tycho Brahe would develop such an unusual system, a Geo-Heliocentric model. The answer was that he couldn't reconcile the Copernican model with the absence of visible stellar parallax. Stellar parallax was an issue for the scientists before and during Galileo's time. Modern discussions of Galileo and the church rarely mention this.
A major tool for cosmology is the Telescope; a device commonly associated with Galileo. In an ironic twist, Galileo's Jesuit contemporaries had made advances in telescope design and construction that would outlast Galileo's own contributions. Christopher Scheiner had opted for a Keplerian design of telescope instead of the popular Galilean design. This would be the design of choice by astronomers within a decade after Galileo's death. Galileo's Battle for the Heaven's does mention Christopher Scheiner, but only to highlight his mistake in believing that sunspots were satellites instead of solar phenomenon.
Modern discussions of the Galileo Affair present a distorted view of seventeenth century cosmology. More importantly, they present a distorted view of seventeenth century science. Galileo was an important scientist of the seventeenth century...he wasn't 'science'. If we look at who the scientists of the 1750's were citing in their work, most would be surprised. Galileo, Kepler and Tycho Brahe did not make it very high in the list. Galileo's contemporary, Gassendi was heavily cited, perhaps because he experimented in many areas of physics and also made important contributions to the philosophy of science. Amongst the most commonly cited were several of Galileo's Jesuit contemporaries, Gaspar Schott, Giovanni Riccioli, and Claude-Francois Deschales [_2_] . Citations by scientists is not a perfect metric for the importance of a scientist but it is better than popularity with public.
A discussion of Galileo would not be complete without mention of the Tower of Pisa experiment. Most people know the legend. A young professor from the University of Pisa climbs the Tower of Pisa in front of an audience of professors and students. In a direct challenge to the stodgy Aristotelian professors of the day, he proceeds to drop balls of unequal weight to show that they hit the ground at the same time. There is a growing consensus that this experiment was a myth, and the program's website questions whether the experiment ever happened. Neither Galileo nor anyone else in his lifetime ever mentioned that Galileo ever performed such an experiment. As with many myths there is a germ of truth to the story. There is documented evidence of a free fall experiment being conducted on the Tower of Pisa in Galileo's lifetime. The twist is that the name of the young professor from the University of Pisa was Vincenzio Renieri, an Olivetan monk. Vincenzio, a friend of Galileo's, was not trying to disprove Aristotle. He was trying to disprove the work of the Jesuit, Niccolo Cabeo. Cabeo believed that two objects of different weights dropped from a height would reach the ground at the same time with the same velocity. This was based on observing the free fall experiments of Baliani. Vincenzio's experiment contradicted that of the Jesuit ( probably through experimental error) and Vincenzio promptly reported the results of his experiments to Galileo. Given how often Galilean biographies are presented as symbols of the clash between church and science, it is ironic that the Galileo's most famous experiment was really just a dispute between an Olivetan monk and a Jesuit priest.