Inter gravissimas
Quick Summary
The papal bull Inter gravissimas, issued by Pope Gregory XIII in 1582, introduced the Gregorian calendar. This reform addressed inaccuracies in the Julian calendar, which had been in use since 46 BCE. The Julian calendar's measurement of the solar year was slightly longer than the actual time, causing seasonal dates to drift by about one day every 314 years. This drift made calculating the date of Easter increasingly difficult. The Gregorian calendar corrected this by adjusting the leap year rule and dropping 10 days in October 1582 to realign the calendar with the seasons. While adopted by Catholic Europe initially, other regions gradually adopted it over time for civil purposes.
Ask Britannica AI about this topic
Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.
Gregory XIIIThe Gregorian calendar…24, 1582, in the bull Inter gravissimas (“In the Gravest Concern”), advanced the date by 10 days (October 4 was to be followed by October 15 that year) and relied on a new method of calculating leap years.
Read More…24, 1582, in the bull Inter gravissimas (“In the Gravest Concern”), advanced the date by 10 days (October 4 was to be followed by October 15 that year) and relied on a new method of calculating leap years.
Read More
calendarThe Gregorian calendarThe papal bull Inter gravissimas (“In the gravest concern”) was issued on February 24, 1582. First, in order to bring the vernal equinox back to March 21, the day following the Feast of St. Francis (that is, October 5) was to become October 15, thus omitting 10 days.…
Read MoreThe papal bull Inter gravissimas (“In the gravest concern”) was issued on February 24, 1582. First, in order to bring the vernal equinox back to March 21, the day following the Feast of St. Francis (that is, October 5) was to become October 15, thus omitting 10 days.…
Read More