When you adopt Hellenismos as a religion, you suddenly have a lot of extra festivals on the calendar. Funnily enough, that's the thing people are most shocked about. In addition to the fancy festivals, however, the Hellenistic base of worship is the monthly lunar calendar (the 'Mên kata Theion', 'sacred month'). Today, I'll present the basic, Hellenistic, monthly calendar. It's constructed from various ancient sources, and is recognized by many Hellenists today.

First Decad - Waxing Moon - Mên Histámenos
1. Noumenia - Selene, Apollon Noumenios, Zeus Herkios and Ktesios, Hestia, and the other Theoi of the Household
2. Agathós Daímōn - Agathós Daímōn
3. Tritomênís - Athena
4. Tetrás - Aphrodite, Eros, Herakles, Poseidon, and Apollon
5. The Erinyes, Eris, and Horkos
6. Artemis
7. Apollon
8. Poseidon, Asklēpiós and Theseus
9. General holy day to honour the Theoi; special day to the Muses, Helios, and Rhea

Second Decad - Middle Moon - Mên Mesôn
11. (1.) The Moirae: Klotho, Lakhesis, and Atropos
12. (2.)
13. (3.) Athena
14. (4.)
15. (5.) Dikhomênía - The Erinyes, Eris, and Horkos
16. (6.) Artemis
17. (7.)
18. (8.) Day of purification
19. (9.) Day of purification
20. (10.)

Third Decad - Waning Moon - Mên Phthínôn
21. (-10) Eikás - Apollon
22. (-9)
23. (-8) Athena
24. (-7)
25. (-6) The Erinyes, Eris, and Horkos
26. (-5)
27. (-4) Triseinás - Impure day
28. (-3) Impure day
29. (-2 -- omitted in Hollow month) Impure day
30. Triakás, Hene kai Nea (Hekate's Deipnon) - Hekate and the dead

Celebrating these sacred days is usually done with a libation of diluted red wine and a hymn to the Theos or Theoi in question. An offering of incense may also be appropriate. Noumenia, Agathós Daímōn and the Hene kai Nea are special celebrations which are celebrated more abundantly. The days of purification are linked to miasma, and katharmos should be applied on these days. Due to the influence of the Underworld on the last days of the month, they are impure, and major celebrations are rarely held on these days.

Hellenic months were either twenty-nine or thirty days in length, since the moon orbits the earth in roughly 29.5 days. Hollow months had twenty-nine days, full months had thirty. The ancient Hellens chose not to alternate the hollow and full months according to a set schedule ("Hekatombaion is a hollow month"), but instead, the duration of each month was declared just before month's end. The thirtieth day was always included; in a hollow month, the twenty-ninth day was left off of the calendar.

Certain days bear special names, based upon their placement within the month. Noumenia (First of the month), Agathós Daímōn (Second), Tritomênís (Third), Tetrás (Fourth), Dikhomênía (Mid-month--on the full moon), Eikás (Twentieth), Triseinás (thrice-ninth (27th)), and Triakás (Thirtieth).

In ancient Hellas, days in the first decad are labeled 'the [number] of the waxing moon', or 'the waxing [number]'. Days in the second decad are labeled 'middle [number]', either from 'middle first' to 'middle ninth', and then on to 'early tenth', or from 'middle one and tenth', to 'middle nine and tenth', then on to 'middle twentieth' (or 'early tenth'). The proper labeling of the last decad is 'the [number] of the waning moon', or 'the waning [number]', but they could be counted back from the coming new moon. 'The waning third', for example, is often considered the twenty-third day of the month, but could be interpreted as the twenty-eighth.

Note that the ancient Hellens started a new day at sundown the day before. Instead of starting a new day at midnight--or in the morning--like we do today, they started it at sundown of the previous day. This means that--when applied to modern practice--the Deipnon starts on the day of the suspected new moon, and the rest follows after, to the total of four days. For more on this, see this post about the Deipnon, Noumenia and Agathós Daímōn. Today, November 27, 2012 is the middle third of Maimakterion, in the forth year of the 697th Olympiad; until the sun goes down, then it's the middle fourth of Maimakterion.

Also important to note is that monthly and annual festivals were rarely held on the same day. This means that every month had an opening and end section where very few--if any--festivals were held, and then the body of the month where festivals stacked (especially around the Athenian new year). Exceptions could be made if the Theos honored during the monthly sacred day corroborated with the Theos honored during the annual festival. The days that we know counted towards days where no festivals were held are bolted in the above list. 9, 11, 13, 15, 16, 21, 23, and 25 may have counted as well.

Modern day Hellenists tend to celebrate annual festivals and monthly holy days on the same day, but I'm strongly contemplating returning to this festival calendar. The timing is not that hard to get right, after all, and it would be a good Recon practice. Hopefully, this post provides you with a starting point for, or expansion of, a fulfilling monthly worship schedule.