Kalendrical Calculations

Caelius has a nice post up on the Golden Number and calculations for Easter and such.

Kalendar arithmetic (the art of the computus) was an important part of the liturgical arts back in the day. Isidore includes astronomy in Book 3 on Mathematics along with music and geometry but puts his section on the Paschal Cycle in Book 6 where he talks about the book and services of the Church. (Here’s a handy fully hyperlinked table of contents for the whole Etymologiae.) Bede wrote two books on time, De Temporibus and the later De Temporum Ratione (see the table of contents here), that teach calendar calculations. The second is the more complete treatment.

Furthermore, this was an important enough matter that the two great English translators of things ecclesiastical into the vernacular—Ælfric and Bryhtferth—both tackled the topic. Indeed, Bryhtferth’s Enchiridion is theoretically a work focused on the calendar and computus but he meanders through all sorts of areas to get there. Ælfric’s De Temporibus Anni is far more lucid, drawing primarily from Bede and supplementing with Isidore.

Where the rubber really hits the road, though are the tables like those that begin on folio 45v of the Leofric Missal… And, hey, as long as you’re poking around those parts of that manuscript, check out the Christ and Satan pictures too.

6 thoughts on “Kalendrical Calculations

  1. Michelle of Heavenfield


    Do you know of a translation of Bede’s first work on Time, the one from c. 703/4?

    I have never read it. So you think that is is more focused on the easter question than his later more extensive work?

  2. Derek the Ænglican

    Well, De Temporum Ratione is, I believe, the earlier one and there is a rather recent translation of it that can be found here at Amazon by Faith Wallis. Helpfully, the table of contents can be viewed at Amazon showing both the contents and a relative length of each section.

    As to whether it has more than the other–I’ll just say it’s been awhile since I looked at either but I believe this one is the more complete.

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