THANK YOU for the reminder. The floating nature of the birthday over what seems to be an unnaturally-extended period always makes this hard to remember. I think we have a post or a thread about this calculation and we need to highlight it every year as the date approaches. If someone finds it before I do please post in this thread and we'll add to the front page notices.
Looks like this may be it: Epicurus' Birthday Calculations
(So you don't have to click through ----)
From Gassendi's Life of Epicurus Check this transcription against the PDF here.
Chap 2. The Time of His Birth
Epicurus was born (as [29] Laertius relates out of the Chronology of Apollodorus) in the 3rd year of the 109th Olympiad, the 7th day of the month Gamelion; at whose birth, [30] Pliny saith, the Moon was twenty daies old. Hecatombeon (the first month) this year falling in the Summer of the year 4372. of the Julian Period, (now used by Chronologers) it is manifest, that Gamelion the same year, being the 7th month from Hecatombeon, fell upon the beginning of the year 4373, which was before the ordinary computation from Christ 341 compleat years. Now forasmuch as in January, in which month the beginning of Gamelion is observ’d to have fallen, there happened a new Moon in the Attick Horizon, by the Tables of Celestiall Motions, the fourth day, in the morning, (or the third day, according to the Athenians, who as [31]Censorinus saith, reckon their day from Sun-set to Sun-set) and therefore the twentieth day of the Moon is co-incident with the three and twentieth of January; it will follow, that Epicurus was born on the 23rd of January, if we suppose the same form of the year extended from the time of Cefar, upwards. And this in the old style, according to which the cycle of the Sun, or of the Dominical letters for that year, (it being Biffextile) was BA, whence the 23rd day of January must have been Sunday. But if we suit it with the Gregorian account, which is ten daies earlier, (now in use with us we shall find, that Epicurus was born on the 2nd of February, which was Sunday, (for the Dominicall Letters must have been ED.) in the year before Christ, or the Christian computation, 341. and consequently in the 1974th year, compleat, before the beginning of February this year, which is from Christ 1634. Some things here must not be passed by.
First, that [32] Laertius observes Sosigenes to have been Archon the same year, wherein Epicurs was born, and that it was the 7th year from the death of Plato. Moreover, it was the 16th of Alexander, for it was, as the same [33] Laertius affirms, the year immediately following that, in which Aristotle was sent for to come to him, then 15 years old.
Secondly, that [34] Eusebius can hardly be excused from a mistake, making Epicurus to flourish in the 112th Olympiad; for at that time, Epicurus scarce had pass’d his childhood, and Aristotle began but to flourish in the Lyceum, being returned the foregoing Olympiad out of Macedonia, as appears from [35] Laertius.
Thirdly, that the error which is crept into [36] Suidas, and hath deceived his Interpreter, is not to be allowed, who reports Epicurus born in the 79th Olympiad. I need not take notice, how much this is inconsistent, not onely with other relations, but even with that which followeth in Suidas, where he extends his life to Antigonus Gonotas: I shall onely observe, that, for the number of Olympiads, Suidas having doubtlesse set down ςθ, which denote the 109th Olympiad, the end of the ς was easily defaced in the Manuscript, so as there remained onely ο, by which means of οθ, was made the 79th Olympiad.
Fourthly, that it matters not that the Chronicon Alexandrinum, Georgius Sincellus, and others, speak too largely of the time wherein Epicurus flourished, and that we heed not the errous of some person, otherwise very learned, who make Aristippus later then Epicurus, and something of the like kind. Let us onely observe what [37] St. Hierom cites out of Cicero pro Gallio; a Poet is there mentioned, making Epicurus and Socrates discoursing together, Whose times, saith Cicero, we know were disjoyned, not by years, but ages.
Fifthly, that the birth-day of Epicurus, taken from Laertius and Pliny, seems to argue, that amongst the Athenians of old, the Civill months and the Lunary had different beginnings. This indeed will seem strange, unlesse we should imagine it may be collected, that the month Gamelion began onely from the full Moon that went before it; for, if we account the 14th day of the Moon to be the first of the month, the first of the Moon will fall upon the 7th of the month. Not to mention, that Epicurus seems in his Will to appoint his birth to be celebrated on the first Decad of the dayes of the month Gamelion, because he was born in one of them; and then ordaineth something more particular concerning the 20th of the Moon, for that it was his birth-day, as we shall relate hereafter. Unlesse you think it fit to follow the [38] anonymous Writer, who affirms, Epicurus was born on the 20th day of Gamelion; but I know not whether his authority should out-weigh Laertius. Certainly, many errours, and those very great, have been observed in him, particularly by Meurfius. I shall not take notice, that the XXXX of Gamelion might perhaps be understood of the 20th of the Moon, happening within the month Gamelion, from Cicero, whose words we shall cite hereafter. But this by the way.
One of Cassius 's favorite Vatican Sayings (attributed to Metrodorus):
VS47 : I have anticipated thee, Fortune, and entrenched myself against all thy secret attacks. And we will not give ourselves up as captives to thee or to any other circumstance; but when it is time for us to go, spitting contempt on life and on those who here vainly cling to it, we will leave life crying aloud in a glorious triumph-song that we have lived well.
I was intrigued by the word translated as "triumph-song." The word (according to Bailey) is παιωνος (paiōnos), an Ionic form of the word παιάν (paian > English "paean"):
Henry George Liddell, Robert Scott, A Greek-English Lexicon, π , πάγ-χαλκος , Παιάν
As the LSJ says, the song had its origin in a hymn to Apollo, the healer of the gods. This has direct relevance to this birthday of Epicurus. DeWitt had said that one of Epicurus's favorite "expletives" was "Paian Anax!" which refers to Apollo as Lord and Healer. (Think of saying something like "Good Lord!" when you're surprised by something or excited.) Epicurus is also a physician in his providing a practical philosophy for the "health of the body and tranquility of the mind." There are also associations with Apollo with picking the 20th as the date of the Epicurean monthly celebrations. And, finally, this 7th of Gamelion (1/10/22) is, according to that calendar link, a feast day of Apollo!
This connection of Apollo with the Epicureans intrigues me and may warrant further research. But that's for later. For now, here are some quick connections between Aphrodite ("patron goddess" of the Epicureans) and Apollo...
Aphrodite and Apollo
https://www.theoi.com/Olympios/ApollonLoves.html
ADONIS A prince of the island Kypros (eastern Mediterranean) who was loved by the god Apollon. Adonis was described as androgynous, acting like a man in his affections for Aphrodite, and like a woman with Apollon.
Pseudo-Apollodorus, Bibliotheca 1. 16 (trans. Aldrich) (Greek mythographer C2nd A.D.) :
"Aphrodite, furious with Kleio . . . caused her to fall in love with Magnes' son Pieros. As a result of their union she bore him a son Hyakinthos. Thamyris, son of Philammon and the Nymphe Argiope, the first male to love other males, fell in love with Hyakinthos. Later on Apollon, who also loved him, accidentally killed him with a discus."
Have you looked into the connection with "Apollo Epicurius", that is, Apollo the Helper?
Ironically, I was trying to determine the other day which architectural order would be proper for Epicureans. I settled on Ionic; there is a temple very near to Samos dedicated to Aphrodite done in Ionic capitals, and Ionia was the birthplace of both atomism and Epicurus.
Built within 20 miles of Samos, dedicated to Aphrodite, done in the Ionic style, and completed during the reign of Hadrian, husband of Plotina, patron of Epicureans—rather fits the bill!
I must correct myself; Plotina was wife of Trajan, not Hadrian. I do rather admire Hadrian, but he doesn't enter into it!
Edit; wrong again! She was Hadrian's adoptive guardian. I need to stop typing and go find some coffee!
I find it impossible to keep Hadrian and Trajan straight in my mind,especially since I gather they both had a wall in England!
For a basic reference on Greek architectural orders:
Have you looked into the connection with "Apollo Epicurius", that is, Apollo the Helper?
And Apollo's epithet of Epicurius is the same word used in Epicurus's name:
Henry George Liddell, Robert Scott, A Greek-English Lexicon, ἐπίκουρ-ος
"helper, ally, protector, patron"
I don't know of any other gods with that specific epithet, so arguably Neocles and Chaerestrate could have been thinking of Apollo Epicurius when they named their son. Maybe Gamelion 7 is always a feast day of Apollo and, if Epicurus was born on that day, naming your son after the god dedicated to that day couldn't hurt. "Hey, we named him after you. Watch over him!"
Here's also an old post of mine that bring out the connection of Apollo with the 20th:
Here is a post from Holly at Facebook earlier this week. It is so frustrating that this is so hard to do:
"I have been following this FB group, and they calculate today as being 5 Gamelion, so the 7th would be Sunday."
https://www.facebook.com/PrayerstotheGodsofHellas
frustrating that this is so hard to do:
LOL! It's actually impossible. I'm surprised two reconstructed calendars can be as close as a day or so. There is no calendar that started in ancient time and remained as a time keeping device to current times.
There's confusion in genealogy research from when the US in the 1700s went from Old Style to New Style dating. It's almost impossible to line up dates that happened over 2,300 years ago.
Just celebrate Epicurus's birthday around this weekend and be done with it. That's as "exact" as we're ever going to get.
Happy birthday, master-builder of human happiness!
My mother in her later years used to stretch her birthday celebration over a couple of weeks: with family on the day, but lunches and such with friends as could be arranged. It's the celebrating that counts 
My grandmother has two birthdays--the day that the government of the United States insists she was born on, and the day that her parents insisted she was born while they were alive!
Martin is suggesting that we just try to develop the closest approximation to our current calendar and forget the moon issue.
Is that possible?
forget the moon issue.
Is that possible?
"Forget the moon" is either a great name for a band or for a poignant memoir. 
Sure, it's possible. There's no way to perfectly calibrate the calendars.
That said, picking a random date in our calendar and sticking to it has precedent: Presidents Day (started as Washington's birthday)... Heck, Christmas is supposed to be Jesus's birthday and that's totally random!
Pick the 7th of December, January, or February and be done is a perfectly feasible solution.
Here is a post from Holly at Facebook earlier this week. It is so frustrating that this is so hard to do:
"I have been following this FB group, and they calculate today as being 5 Gamelion, so the 7th would be Sunday."
https://www.facebook.com/PrayerstotheGodsofHellas
So, basically what we have here are two Hellenic reconstructionist neo-pagan groups coming up with two slightly different calendars.
I'm sticking to the original one I posted from Hellenion since they linked to (what seems) some authoritative sources for their calculations. But, in the end, we're all pretending we can pinpoint a birthday that happened 2,300+ years ago to the day.
As someone said here, it's the celebration (and commemoration) that counts.
Now forasmuch as in January, in which month the beginning of Gamelion is observ’d to have fallen, there happened a new Moon in the Attick Horizon, by the Tables of Celestiall Motions, the fourth day, in the morning, (or the third day, according to the Athenians, who as [31]Censorinus saith, reckon their day from Sun-set to Sun-set) and therefore the twentieth day of the Moon is co-incident with the three and twentieth of January
I point to this excerpt here to illustrate what we're up against. "The fourth day... Or the third day, according to the Athenians..." Do we calculate sunset to sunset? Sunrise to sunrise? New moon to New moon?
That "Athenian" calculation could make the difference between Sunday or Monday easily; however, I realize Gassendi is trying to say they were the same day just arrived at by two different calculations.
Gassendi's calculation strikes me as similar to the Usher's attempt to calculate the day of Creation
at least Gassendi was trying to calculate a real person's birthday.
Don so what do you conclude to be the closest modern calendar equivalent?
