ATTI DELLA SOCIETÀ DEI NATURALISTI E MATEMATICI DI MODENA
Abstract
In the Gregorian calendar, the length of the mean tropical year is implicitely defined as 365 + 97/400 solar days. The present work is a contribution to the studies on the origin of the fraction 97/400. We assume that the reform used the experimental value of the tropical year given in the Alphonsine Tables. Then we show that a direct computation of two best rational approximations of the fractional part r = 5h49′16′′ of the Alphonsine year, together whith a simple interpolation formula well–known to old calendarists, would have given precisely the fraction 97/400.
