(Author’s Note: This is largely based off of the AD calendar. Just with a more religious feel. I got the idea from reading up on fantasy calendar generation, and it is kinda silly, but maintains some continuity with our existing calendar. As for the date about city on the hill – we don’t know. It was during the time, but we don’t apparently know the exact day.)
Expecto Domini (ED)
This calendar was originally just the calendar of an offshoot of the Third Reformed Presbyterian Church, which formed in Armstrong Dome shortly after the 22nd century AD started. As the moon has no real “days”, they continued to use the calendar most of them were familiar with. The first leader of the church, Lunar Adminstrator Thomas Shalan, selected the first day as the 19th of June, 1630 AD. He claimed it was the date that John Winthrop gave his speech about a city on the hill.
Unlike most calendars, though, this calendar counts down to 0. At the time, the Regolith Anamoly had been found during construction of Cernan Dome. Inscribed in a language that was undecipherable at the time, Shalan claimed to have been divinely ordained in how to translate it. Performing the calculations, he calculated the 0 point as 19 June 2730.
The calendar itself is almost always out of sync, especially on leap years from the AD calendar.
Adoption and Use
It was never adopted by the Solar Union. Not until the Fall of Earth did it begin to see use as the Holy Protectorate of Sol – from the three remaining Lunar domes on the Moon’s dark side – was really the only people left outside the outposts and habitats within the Kupier Belt. With the necessary economic and military power, the Holy Protectorate of Sol began to impose it’s culture – and thus it’s calendar – on the rest of the system.
(ETA: small typo detected)