Source Card — Inter gravissimas (1582)
Gregory XIII, papal bull, 24 February 1582
The founding document of the Gregorian calendar, stating the ten-day deletion, the century leap rule and the Paschal motive in the pope's own decree.
Publisher and date
Promulgated by Pope Gregory XIII, 24 February 1582, taking effect in October 1582 in adopting states. The technical scheme is credited to Aloysius Lilius and was defended and elaborated by Christopher Clavius.
What to read it for
The stated reason is the correct celebration of Pascha and the restoration of the vernal equinox to 21 March. Both the solar (leap-year) and lunar (epact) corrections are in the document, which is why treating the reform as purely a solar fix understates it.
Citations on this file
Sources
- Inter gravissimas — Latin text and English translationFourmilab's annotated edition of the bull, with the calendar arithmetic explained.https://www.fourmilab.ch/documents/calendar/ ↗
Links are pointers for further reading. The claim is what is sourced, not the website.