One of the first challenges people find when looking into Hellenismos, is sorting out the calendar. It’s so easy and personal it’s overwhelming, so people go for the super complex answer – try to do the ENTIRE festival schedule of a large diverse city like Athens!
Take a deep breath, step back, and reflect on what we know:
1) Each city-state and demos had their own calendar. Even their own names for the months in different areas. We also know that when new colonies were started, no matter what the parent state, the new colony made their own calendar. There is a great wiki article about both the Athenenian/Attic calendar, and the various others in ancient Hellas. Consider yourself a proto-demos of one, one new colony.
2) The ancient Athenians were remarkably relaxed about their calendar by our standards. They would extend a month here, take away some days there. Other things like the May harvest of barley was so localized to each microclimate, that they had the thanksgiving festival when it suited them. The date was not written in stone (yes, archeologists have the stone calendar of Eleusis, for example. It’s a difficult book (“A Sacred Calendar of Eleusis” By Sterling Dow, Robert F Healey, S.J.) , and Reif’s “Mysteries of Demeter” does a VERY nice job of summarizing the material.)
3) The ancients didn’t have email, so the statement “while Greek months were supposed to begin with the first sighting of the new moon, this was determined locally and with a degree of variability” couldn’t be more true!
We suggest people only take on what they will feel successful with. If you start with small regular steps, then you will gain momentum and be able to add more rituals over the years. If you take on too much at first, guilt and frustration probably won’t be feelings that will inspire a personal practice for long.
Take a look at the Hellenion calendar, (the web version is easiest) and see what works for you. There is probably a particular god you feel especially motivated to honor, so look at their festivals and start there. Or you could start at the new moon.