ComputusComputus (Latin for “computation”) is the...
Computus
Computus (Latin for “computation”) is the calculation used to determine the calendar date of Easter. Because the date is based on a calendar-dependent equinox rather than the astronomical one, there are differences between calculations done according to the Julian calendar and the modern Gregorian calendar. The name has been used for this procedure since the early Middle Ages, as it was considered the most important computation of the age.
[Don’t forget to check out the Gauss algorithm and the use of his (clever) modular arithmetic]
Image caption
Chronological diagram of the date of Easter for 600 years, from the Gregorian calendar reform to the year 2200 (by Camille Flammarion, 1907). High-res.