Key figures and paths in the history of the calendar
The history of the calendar spans generations, institutions and scientific traditions. Pietro Pitati, Luigi Lilio, Christoph Clavius and Gottfried Kirch make it possible to explore different moments of this path: the proposals for correction, the drawing up of the reform, its mathematical explanation and the culture of calendars in later Europe.
Pietro Pitati: the sixteenth-century proposals
Pietro Pitati, known in Latin as Petrus Pitatus, was a scholar from Verona active in the first half and middle decades of the sixteenth century. He worked on astronomical observations, tables and the calculation of Easter.
In his Compendium of 1560, reissued in 1564 and under a different title in 1568, he addressed the correction of the calendar. Among his proposals was the suppression of three leap days every four centuries, with a distribution of century years different from the one later adopted.
Comparison with Lilio requires examining separately the solar rules, the lunar procedures and their respective purposes. Mathematical similarities must be studied together with chronology and the evidence for the circulation of the texts.
Luigi Lilio: the structure of the project
Lilio holds a central position in the proposal presented in the Compendium of 1577. His tables make it possible to study how the solar correction and the lunar computation were coordinated within a single system.
The comparison between this document, the earlier projects and the reform as promulgated is one of the Centre's main lines of research.
Christoph Clavius: explaining and defending the reform
The Jesuit Christoph Clavius, known in Italian as Cristoforo Clavio, was a mathematician at the Collegio Romano and a member of the calendar commission.
His Romani calendarii a Gregorio XIII P. M. restituti explicatio, published in 1603, is a fundamental source for understanding the rules of the reformed calendar and the arguments with which they were explained and defended.
Gottfried Kirch: astronomy and calendars in later Europe
Gottfried Kirch, who lived from 1639 to 1710, belongs to a later phase. As an astronomer and calendar author, he makes it possible to extend the study to observational practices, networks of correspondence and the spread of astronomical knowledge between the seventeenth and eighteenth centuries.
His letters and calendars document a world in which the calculation of time met book production and the needs of readers.
The Study Centre's method
The Centre connects these paths through the examination of sources, the comparison of editions and the reconstruction of calculation procedures. Each study distinguishes documented facts from interpretations, indicating the references that allow readers to verify and continue the research.