What is Computus?

In the year 325 a council of Bishops, no more than 295 years removed from the death of Jesus Christ, convened to forge the first documents unifying Christian doctrine. Summoned to the City of Nicaea by Roman Emperor Constantine I, the Bishops crafted the first shards of a deeper theological consensus within the Churches of Christendom.

This First Council of Nicaea produced an authoritative body of literature on Christian beliefs and settled several inter-faith debates. They also established that a majority of the council desired a church computation of the date of Christ's resurrection.

Traditionally Christians relied on Jewish communities to inform them when Passover fell, as Christians observe that Christ’s crucifixion and resurrection took place over the Passover holiday. The Council of Nicaea set out two rules for the new computation: That it must be independent of the Jewish calendar, and that it must be uniformly applicable worldwide. No other details were specified.

Computus, as it is now known, is the act of attempting to generate a sufficient algorithm or table with which to judge the date of Easter in any given year.

Computus.app provides access to and explanations of three such calculators: the Latercus (~4th/5th century), Dionysius Exiguus’s Easter Table (525), and Carl Friedrich Gauss’s Easter Calculator (1800).