Astograthian calendar

The Astograthian calendar (Astograthian: Egutegia Astograthiko) is a solar calendar used in Astograth, where it is co-official together with the Gregorian calendar used internationally.

The Astograthian calendar consists of 13 months of 28 days each, plus a New Year's Day (Ospakizuna, 'celebration') not counted as part of any month; this adds up to 365. In leap years, an additional holiday (Ordaintzea, meaning 'repayment' or 'thanksgiving') is inserted after the end of the ninth and before the tenth month. This lines up with 29th February in the Gregorian calendar. Leap years are calculated in the same way as the Gregorian calendar: every year that is a multiple of 4 is a leap year, except for years that are multiples of 100 unless they are multiples of 400. Weeks are 7 days long.

The Astograthian calendar maintains a stable correspondence with the Gregorian calendar; 7th Kimuanil will always correspond to 23rd August, for instance, and the Astograthian year always begins on 21st June. Days and months can be expressed using either calendar in this way, although in Astograth the year is always counted according to the Astograthian calendar's epoch; thus, 1 January 688 and 31 December 689 take place in the same Gregorian year. Year 1 of the Astograthian calendar is counted from the first year after the Battle of Aratzalbarra; years are denoted as being After Aratzalbarra (A.A.) or Before Aratzalbarra (B.A.).

The Astograthian calendar was first devised by positivist philosopher, mathematician, and astronomer Asteri Berroyalbis of Letzama in year 388 A.A. With minor revisions, it was adopted in 456 by signatory states of the Arbetsana Protocol, which standardised weights and measures among members of the League of Astograth. The present Astograthian state, which evolved out of the signatory Duchy of Rumiatzi, maintains the use of the Astograthian calendar as outlined in the original protocol.

Months
All Astograthian months officially last 28 days. New Year's Day (Urteberrearen Ospakizuna), on 21 June in the Gregorian calendar, is counted outside of the month system. In Astograthian date notation it is rendered with the day and month number zero (0); Ospakizuna of the year 688 is thus written 0/0/688 or 688-0-0. In leap years, the additional monthless day of Ordaintzea is inserted between the 9th and 10th months. In date notation this is officially represented with the currency symbol for Diru (Đ), thus Ordaintzea of the year 688 is written Đ/Đ/688 or 688-Đ-Đ. Unofficially, it is commonly represented as the 29th day of the 9th month; this use is widespread even in Astograthian government databases, though officially discouraged. The 9th month, Sagarranil, lines up exactly with February of the Gregorian calendar; the 10th month, Mahatsenil, is in synchrony with March until the end of Mahatsenil on 28th March.

The names of the months were devised by Asteri Berroyalbis in his 388 proposal, retaining Urtarril for the first month of the year, Ekain for the hottest month of the year, and Ospakizuna for the New Year holiday from the traditional Astograthian calendar. The rest are of his invention, named after the natural world and traditional agriculture. Berroyalbis' original proposal for the leap year was to create the secular holiday of Ereinotzaren ('of laurels'), avoiding the traditional name of Ordaintzea due to its use in the Astograthian folk religion. This was discarded by the signatories of the Arbetsana Protocol, which instituted Ordaintzea as the name for the leap year holiday.

Days of the week
The Astograthian week has 7 days, which correspond exactly with those of the Gregorian calendar. The special days of Ospakizuna and Ordaintzea, though outside of the month cycle, are counted within the week cycle, which avoids dates being fixed to specific weekdays as in certain other 28-day-month calendars.

The names of the days of the week were adopted by the Arbetsana Protocol in 456 with one change to Berroyalbis' 388 proposal. As in Berroyalbis' design, the name Astelan for the first day is retained from the traditional Astograthian calendar, which had four-day weeks, and takes names from the natural world for the remaining six days. His proposal for the seventh day, Eguzkiaren ('of the Sun'), was replaced by Atseden ('of rest').