The Sun in the Church: Cathedrals as Solar Observatories

Article excerpt

The Sun in the Church: Cathedrals as Solar Observatories. By John L. Heilbron. (Cambridge, Massachusetts: Harvard University Press. 1999. Pp. ix, 355; 8 plates. $35.00 clothbound; $18.95 paperback.)

A close examination of the relationship between Catholic ecclesiastical patronage and the development of the natural sciences in Italian cities during the century after Galileo has long been missing. John Heilbron's investigation of the evolution of cathedrals or Duomos as significant solar observatories contributes impressively to that study Heilbron reveals that Church leaders, motivated chiefly by a need for improved calendrics, financially assisted greater achievements than previously thought in observational astronomy and mixed mathematics in Italian cities in the late seventeenth century. Records from Italian cathedrals in Bologna, Florence, and Rome, along with St. Sulpice in Paris, are the major sources for Heilbron. His book combines ecclesiastical history and the history of science with astronomy, mixed mathematics, and architecture.

Heilbron first reviews germane developments in astronomy from Ptolemy to Copernicus, Kepler, and Galileo, finding "shameful" the Church's treatment of Galileo. Yet Heilbron scarcely considers studies of Galileo after 1990, such as Mario Biagioli's, and does not explore the influence of the Thirty Years' War upon the Papacy. He then recounts the scandals over calculating the date of Easter from antiquity and Pope Gregory's calendar reform in 1582 supported by meridiane results on equinoxes. The size of cathedrals and their likeness to a camera obscura made them a powerful locus for meridiane, properly placed holes in cathedral roofs that determined the position of a rod on the floor as it marked the movement of the stuttering light from the sun's transit during the year. A solar year is complete when the line crosses itself. But the length of the solar year is 365.2422 days and obtaining a precise approximation was challenging. …