Module coptic 

Coptic (Alexandrian) calendar.

Implements the Coptic calendar with Julian Day Number conversions, following the algorithms in Dershowitz & Reingold, Calendrical Calculations (4th ed., Cambridge University Press, 2018), ch. 4.

Historical Context

The Coptic calendar descends from the ancient Egyptian civil calendar, reformed under Augustus in 25 BCE to add a leap day every four years. It has 12 months of 30 days each, plus a 13th short month (Nasie / Pi Kogi Enavot) of 5 days (6 in leap years). The Coptic era (Anno Martyrum) begins on August 29, 284 CE Julian, commemorating the accession of Diocletian and the era of Christian martyrs in Egypt.

The Ethiopian calendar shares this structure but uses a different epoch (August 29, 8 CE Julian) and month names.

Structs

CopticDate

A date in the Coptic (Alexandrian) calendar.

Enums

CopticMonth

The 13 months of the Coptic calendar.

Constants

COPTIC_EPOCH_JDN

Julian Day Number of the Coptic epoch: 1 Thout, Year 1 AM (Anno Martyrum) = August 29, 284 CE Julian.

Functions

coptic_is_leap

Whether a Coptic year is a leap year.

coptic_to_jdn

Convert a Coptic date to a Julian Day Number.

coptic_year_days

Days in a Coptic year (365 common, 366 leap).

jdn_to_coptic

Convert a Julian Day Number to a Coptic date.