Gregorian calendar reform changes solar reckoning and Easter tables
About this date: The marker dates the promulgation and first implementations, not a simultaneous worldwide change. Later civil adoption and a church's liturgical practice are separate questions.
Gregory XIII's Inter gravissimas orders a calendar correction and revised paschal reckoning. The reform is a Catholic papal act whose wider civil and ecclesial reception takes place over time.
Historical context
The reform aims to correct the drift between the calendar and the seasons and to revise lunar reckoning for Easter. In the initial October implementation, 4 October is followed by 15 October. A changed civil date label does not mean that ten elapsed days were removed from human lives.
Key points
- Solar-calendar correction and the tables for the paschal moon address related but distinct cycles.
- The Gregorian leap-year rule omits century leap days unless the year is divisible by 400.
- The papal decree, a government's later civil adoption, and a church's liturgical reception must not be collapsed into one event.
People
- Gregory XIII
- Aloysius Lilius
- Christopher Clavius
Sources and further reading
- Introduction to Calendars
Contrasts Julian and Gregorian leap-year rules and explains why solar years and lunar months require different calculations. - Inter gravissimas
Read the decree's stated purposes and its order that 4 October be followed by 15 October. This dossier paraphrases rather than reproduces the modern translation.