Meridian lines in European churches, the date of Easter, and the use of Copernican mathematics: J. L. Heilbron's "The Sun in the Church"

Over twenty years ago, I read J. L. Heilbron's "The Sun in the Church: Cathedrals as Solar Observatories." The Catholic Church's concern for the correct date for Easter led to the installation of a single hole in church roofs through which sunlight would shine on a "meridian line" on the floor at noon every day. This identified the vernal equinox and thus Easter (the first Sunday after the first full moon after the equinox). Heilbron also pointed out that the Church actually encouraged the use of Copernican mathematics in astronomical calculations – as long as no claims were made that the heliocentric system actually corresponded to the physical structure of the universe. (Andrew Shields, #111words, 10 January 2022)

 

The meridian line at Santa Maria degli Angeli e dei Martiri, Rome