A Guide to “The Sun in the Church” by J.L. Heilbron



Meridian Line. S. Petronio, Bologna, Calter Photo	Analemma at S. Petronio, Bologna	Solar eclipse at the Meridian line at S.Maria degli Angeli in Rome by Mario Catamo

The Sun in the Church: Cathedrals as Solar Observatories by J.L. Heilbron is an extremely interesting book. Unfortunately, it is not easy to read. It contains both serious mathematics and serious history. The purpose of this page is to assist people who want to read it.

For a quick summary, start with either How the Church Aided 'Heretical' Astronomy (with graphics) or Churches as scientific instruments by J. L. Heilbron, Annual Invitation Lecture to the Scientific Instrument Society, Royal Institution, London, 6 December 1995, published in Universitas, Newsletter of the International Centre for The History of Universities and Science, no. 9, April 1996.

For help with the astronomy, please consult my student NG Yoke Leng's undergraduate research project A Mathematical Supplement to “The Sun in the Church, Cathedrals as Solar Observatories” by J.L. Heilbron. The project is a web page, but here is a printer friendly PDF version. Yoke Leng also did a project with me on Easter computations.

My student THAM Peck Fun did an honours project on Bisection Of The Eccentricity. We went a bit further (and corrected some minor errors in Yoke Leng's thesis). At least one error remains. On page 32 and 34 she says that "the smaller circle should be 1/15 that of the bigger circle." It should be sine of 23.5.

If you have a hard time keeping track of the different meridiana mentioned in the book, this table may be useful. Remember to check out the links to the web pages about the meridiana of some of the individual churches.


City	Church	Designer	Year	Page	Figure and Plate
Florence	S. M. Novella	Danti	1674	P. 68	Fig. 2.28, 2.29
	Santa Maria del Fiore (additional link)	Toscanelli	1475	P. 70	Plate 1 (p. 70), 6
		Ximenes	1755	P. 226	Fig. 2.30
Bologna	San Petronio	Danti	1576	P. 72	Fig. 2.31
		Cassini	1655	P. 89	Fig. 3.4, 3.5, Plate 2 (p. 72), 4
		Cassini	1695	P. 137
		Zanotti	1776	P. 138
The Vatican	Torre dei Venti	Danti	1576	P. 79	Plate 3 (p. 79)
Rome	Santa Maria degli Angeli	Bianchini	1703	P. 147	Plate 5 (p. 156)
Paris	Observatory	Giovanni Domenico (Jean Dominique) Cassini	1671	P. 143	Fig. 3.1
		Jacques Cassini	1729	P. 173
	Saint Sulpice	Lemonnier	1742	P. 220	Fig. 7.1, 7.3
Milan	Duomo	Cesaris	1786	P. 266
Palermo	Duomo	Piazzi	1801	P. 272	Plate 7 (p. 273)