The Arcane Calendar

Seeing such sacred powers of two as 8, 16, and 32 finally gain significance in date-keeping filled the mathematician in me with joy. It almost made up for the razing of my hometown during the unification campaign... But not quite.
— Professor Angrin Tollex, from his cell in the dungeons of Al-Voyanna

The "Arcane" calendar predates the Velpyrian Empire, the great houses, and many of the kingdoms they united. All variations of the arcane calendar share the same 11 months. The contemporary standardised calendar used across the Velpyrian Empire allocates these 11 months 32 days each. Each month comprises 4 weeks of 8 days. Each fortnight of 16 days (of which there are 22 per year) corresponds to one of the "Major Arcana" named cards of the cartomantic tarot deck.

Since a full year consists of 365 days, there is left a "monthless" 9-day period which falls after the 32nd day of the eleventh month of Sannalais, and ends on the 365th day of the year, before the 1st day of the first month of Expos of the next year. This monthless period is known colloquially as Navratri or "The Nine Nights of The Moon" and is a time of many rituals and celebrations across Istolairian cultures.

The 11 months of the standard arcane calendar and their Major Arcana are listed below (using the ever-popular Crezentine tarot deck).

Expos, The First Month
Statuus, The Second Month
Incidé, The Third Month
Demiss, The Fourth Month
Hausse, The Fifth Month
Refeux, The Sixth Month
Prosé, The Seventh Month
Kalavaire, The Eighth Month
Cristal, The Ninth Month
Tern, The Tenth Month
Sannalais