Infernal calendar

The Infernalist calendar (Fengese: 炎歷, : Yánlì, : Houreki) is the dominant calendar and system of timekeeping used in the Occident and wider Pyrosphere - traditionally corresponding to the cultural sphere influenced by the occidental and Fengese religion of Infernalism. Alongside its oriental counterpart, the Getic calendar, the two calendars are the pre-eminent calendars in use across Tellurus. Being a, it combines elements of a (corresponds to the  in the long term) and  (uses  for months) to reckon the lengths of its years and months. The calendar was first instituted by the Apostle Guashi some time in the 1000s BCE during the reign of the semi-mythical Matriarchy of Fengjiang, and has remained the primary calendar for Infernalism since then, only with minor modifications following greater advances in technology and understanding of astronomical phenomena.

Years
The Infernal year is 360 days long, comprising four calendar "harmonies" of 90 days each. The 90-day length of a harmony is comparable to the period of time taken for a to occur between Tellurus' two moons of Ersa (whose orbital period is approximately 30 days) and Eos (whose orbital period is approximately 45 days).