Reception Of Revolutions

The invention of printing by Johannes Gutenberg (1398—1468) in 1475 resulted in a large increase in the number of books in circulation and greatly increased the distribution and influence of individual books. Revolutions was printed in 1543 in Nuremberg, a second edition followed in 1566 in Basel, and a third in 1617 in Groningen. Questions have been raised by scholars concerning how widely and how closely this very technical treatise was read, and its publication was not accompanied by any particular flurry of work on the kinematics of planetary motion. (Arthur Koestler [1963, 191] referred to Revolutions as "the book that nobody read.") Nevertheless, the first two editions, already preceded by Rheticus's expository First Narrative of 1540, ensured that the idea of the heliocentric system was disseminated widely throughout Europe in the second half of the sixteenth century.

Copernicus's procedure in Revolutions was to recast the Ptolemaic models within a heliocentric framework, and some commentators have suggested that he simply rewrote the Almagest from a heliocentric perspective. Copernicus's treatise was used as the basis for the construction of a new set of astronomical tables by Erasmus Reinhold (1511-1553) in 1551. The Prutenic tables superseded the traditional Alphonsine tables based on Ptolemaic theory. The publication of these tables attracted attention to the heliocentric system. Because Copernicus used more accurate parameters than Ptolemy, he obtained better results than those which would result from the Almagest theory, but such improvements could also have been achieved within an updated Ptolemaic system. Copernicus's insistence on modeling all motions out of a combination of uniform circular motions also meant that there were definite limits on the degree of observational accuracy that could be reached in his system.

The observational basis of the Copernican system would only be solidified later with the invention of the telescope. There were nevertheless certain observational facts that tended to support the heliocentric hypothesis. For example, Copernicus recognized that there were some problems with the Ptolemaic positioning of Venus below the Sun, with the fact that the distance to the Sun in the Ptolemaic system is supposed to be always greater than the distance to Venus. It was evident from the cycle of the Moon's phases that the light we receive from it is reflected from the Sun. It would be natural to suppose that the planets also shine by reflected light from the Sun, and the changing pattern of brightness of the outer planets is consistent with this hypothesis. In the case of Venus, however, there should, in the Ptolemaic system, be very considerable changes in its brightness. In particular, when it lies on points on its epicycle close to the line from the Earth to the Sun, it should appear very much dimmer than it does when it is at maximum elongation from the Sun. It was known from observation that there was only a fairly small variation in the brightness of Venus. In chapter 10 of book one of Revolutions Copernicus pointed out that it was necessary for those who placed Venus below the Sun to suppose that the planets shine by their own light, or at least emit light received from the Sun over their whole surface. Even in this case, there would be substantial changes in the brightness of Venus resulting from the large changes that occur in its distance to the Earth. Overall, the hypothesis of reflected light seemed more likely. The positioning of Venus relative to the Earth in the heliocentric system, where the decreasing brightness of Venus as it moves away from the Earth is compensated for by the greater visibility of its illuminated surface, would account for the constant brightness of Venus. This fact was confirmed observationally by Galileo in 1609, when he observed the phases of Venus through his telescope.

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