Byzantine Lunar Calendar

After a blog post in which I said programming a lunar calendar would be a pain in the butt and I wasn't going to do it... I did it.

I decided to mix and match some things from history, and going back far enough that I'd always be dealing with positive timestamps. Dealing with negatives is just too much of a hassle for something I do in my spare time for fun.

I settled on a lunar calendar that started in March (the pre-Caesar calendar's starting point, when September and the rest made sense) at midnight after the new moon on what we call March 6, 330 CE. Constantinople became the capital of the Eastern Roman Empire (a.k.a. the Byzantine Empire) on May 11 of that year, which I picked to be Year One. Like the current Islamic calendar, it's purely lunar, with no correction to keep it aligned with the solar year.

Unlike the Islamic calendar mine works on alternating month lengths of 30 and 29 days, with the twelfth month occasionally adding a 30th day to realign itself with the phases of the Moon.

That set of leap days (7 every 19 years) is pretty close to perfect, it only gains a day every 45 of those 19-year cycles -- 855 years. To balance it back out I skip the leap year on the 853rd year of the cycle.

I also use the Latin names for the months and the days of the week, and Roman numerals for dates, years, hours and minutes. The abbrev­iations "d." and "m." are for the Latin words "dies" ("day") and "mensis" ("month") which the sites I used to get the names added so I figured they must be important.

And since Roman numerals have no concept of 0, I added an "n" ("nullus") where the clock would normally have a zero.

Some important dates are below, in both CE and BE ("Byzantine era")

Current Byzantine Lunar Date
Calendar start
7 March 330 CE
Constantinpole becomes capital of the Eastern Roman Empire
11 May 330 CE
Fall of Rome/­Odoacer becomes king of the Western Empire
4 September 476 CE
Constantinople conquered by Ottomans
29 May 1453
Formation of Turkish Republic
29 October 1923