Science Rather Than God: Riccioli's Review of the Case for and against the Copernican Hypothesis

... [he was] an enemy to the Copernican system, and has the discredit of having measured the evidence for and against that system, not by the weight but by the number of the arguments.... '. . . Riccioli put forward a series of arguments in contradiction of the Earth's movement . . . marvellously absurd. "Would the birds . . . dare to rise in the air if they saw the earth passing away from beneath them?" From such a specimen we may judge of the rest of the egregious structure. . .. 2. . . Riccioli's treatment of the cosmological controversy was a sterile exercise. Astronomical issues could no longer be settled by a preponderance of scientific and scriptural authority or by any number of decrees from Rome.3 In Riccioli's ultimate acceptance of the immobility of the earth, biblical and theological arguments proved decisive.4[Riccioli] produced forty-nine arguments that were in favour of heliocentrism, and seventy-seven that were against, and thus the weight of the argument favoured an earth-centred cosmology!5These quotations, dating from the early nineteenth to the early twenty-first century, illustrate the long-standing reputation of the Italian Jesuit astronomer Giovanni Battista Riccioli (1598-1671), as concerns his analysis of the case for and against the Copernican hypothesis in his 1651 Almagestum novum. This reputation is undeserved. Contrary to these statements, Riccioli's analysis was not based on the number of arguments but on their weight; it was not absurd; it was not dependent on either authority or scripture. Rather, it hinged on two key arguments - both scientific in nature, both difficult to refute at the time, and both destined to be matters of scientific investigation into the nineteenth century, long after the debate over the world system hypothesis was settled. Riccioli's work illustrates an interesting aspect to that debate: that the geocentric hypothesis, in the form advocated by Tycho Brahe, was backed by real and strong arguments in 1651.Riccioli discusses 126 arguments in his analysis in Almagestum novum: 49 proCopernican, 77 anti-Copernican.6 For each argument, Riccioli provides the opposing side's response to that argument, if he believes a valid response exists, as is usually the case. Thus, while Riccioli does note the issue of birds keeping pace with a moving Earth as an anti-Copernican argument, he also notes that there is a simple response to this argument - that the Earth, the birds, and the air all share a common motion.7 Thus Riccioli is not presenting the birds issue as an argument having real weight, but as simply an argument that has been proffered in the world system debate.Such is the case with those arguments Riccioli presents that relate to matters of theology, scripture, or religious authority. Perhaps surprisingly, only two of the 126 arguments relate to such matters. Both are anti-Copernican. One states that if Earth is not the centre of the Universe, then Hell is not at the lowest place, and someone going to Hell could, conceivably, ascend in so doing!8 The other states that, according to Scripture, the eclipse of the Sun at the death of Christ was total for three hours (see Mark 15:33), yet if the Earth had a diurnal rotation, such an eclipse would not be possible: the diurnal rotation would quickly have carried Palestine out of the Moon's shadow, so ending the eclipse.9Riccioli says there are valid responses for both of these. The response to the first is to note that Hell is a place defined by comparison, to "this world on which men travel" and to "God's Heaven", and the relationship between Heaven, Hell, and the world of men is not affected by whether Earth moves.10 The response to the second is simply that the motion of the Moon could have been altered so as to compensate for the Earth's rotation, as it presumably would have been altered so as to produce a three-hour eclipse even were the universe geocentric." Riccioli presents neither of these anti-Copernican arguments as having any weight. …