It is generally held that the full moon falls in the middle of the month; either the 14th or the 15th - this page attempts to analyze exactly where the 100% full moon falls in these four methods; as well as the quarters.
Now, if we apply Scripture:
Gen 1:14 And Elohim said, “Let lights come to be in the expanse of the heavens to separate the day from the night, and let them be for SIGNS and APPOINTED TIMES, and for days and years,
Lev 23:2 “Speak to the children of Yisra’el, and say to them, ‘The appointed times of Yahuah, which you are to proclaim as set-apart gatherings, My APPOINTED, are these:
Lev 23:3 ‘Six days work is done, but the seventh day is a Sabbath of rest, a set-apart gathering. You do no work, it is a Sabbath to Yahuah in all your dwellings.
Exo 31:13 “And you, speak to the children of Yisra’el, saying, ‘My Sabbaths you are to guard, by all means, for it is a SIGN between Me and you throughout your generations, to know that I, Yahuah, am setting you apart.
Eze 20:12 “And I also gave them My Sabbaths, to be a SIGN between them and Me, to know that I am Yahuah who sets them apart.
Eze 20:20 ‘And set apart My Sabbaths, and they shall be a SIGN between Me and you, to know that I am Yahuah your Elohim.’
Psa 81:3 Blow the ram’s horn at the time of the New Moon,At the full moon, >ON< our festival/CHAG day.
Exo 12:6‘And you shall keep it until the fourteenth day of the same month.Then all the assembly of the congregation of Yisra’el shall kill it between the evenings.
Exo 12:7 ‘And they shall take some of the blood and put it on the two door posts and on the lintel of the houses where they eat it.
Exo 12:8 ‘And they shall eat the flesh on that night, roasted in fire – with unleavened bread and with bitter herbs they shall eat it.
Exo 12:9 ‘Do not eat it raw, nor boiled at all with water, but roasted in fire, its head with its legs and its inward parts.
Exo 12:10 ‘And do not leave of it until morning, and what remains of it until morning you are to burn with fire.
Exo 12:11 ‘And this is how you eat it: your loins girded,your sandals on your feet, and your staff in your hand. And you shall eat it in haste. It is the Passover of Yahuah.
Exo 12:12 ‘And I shall pass through the land of Mitsrayim on that night, and shall smite all the first-born in the land of Mitsrayim, both man and beast. And on all the mighty ones of Mitsrayim I shall execute judgment. I am Yahuah.
Exo 12:13 ‘And the blood shall be a sign for you on the houses where you are. And when I see the blood, I shall pass over you, and let the plague not come on you to destroy you when I smite the land of Mitsrayim.
Exo 12:14 ‘And this day shall become to you a remembrance. And you shall observe it as a festival/CHAG to Yahuah throughout your generations – observe it as a festival/CHAG, an everlasting law.
The 14th is a CHAG...
Lev 23:6 ‘And ON the fifteenth day of this month is the Festival/CHAG of Unleavened Bread to Yahuah – seven days you eat unleavened bread.
The 15th is a CHAG..
Lev 23:34“Speak to the children of Yisra’el, saying, ‘On the fifteenth day of this seventh month is the Festival/CHAG of Booths for seven days to Yahuah.
The 15th is a CHAG...
"full moon,>ON< our festival/CHAG day."
Philo had to say...
In Allegorical Interpretation, 1IV (8), it says…
“Again, the periodical changes of the moon,take place according to the number seven, that star having the greatest sympathy with the things on earth. AND THE CHANGES WHICH THE MOON WORKS IN THE AIR, IT PERFECTS CHIEFLY IN ACCORDANCE WITH ITS OWN CONFIGURATIONS ON EACH SEVENTH DAY. At all events, all
mortal things, as I have said before, drawing their more divine nature from the heaven, are moved in a manner which tends to their preservation in accordance with this number seven. … ACCORDINGLY, ON THE SEVENTH DAY, ELOHIM CAUSED TO REST FROM ALL HIS WORKS WHICH HE HAD MADE.”…
The Decalogue XXX (159),
“But to the seventh day of the week he has assigned the greatest festivals, those of the longest duration, at the periods of the equinox both vernal and autumnal in each year; appointing two festivals for these two epochs, each lasting seven days; the one which takes place in the spring being for the perfection of what is being sown, and the one which falls in autumn being a feast of thanksgiving for the bringing
home of all the fruits which the trees have produced”…
Special Laws I. (178), Philo writes…
“…there is one principle of reason by which the moon waxes and wanes in equal intervals, both as it increases and diminishes in illumination; the seven lambs because it receives the perfect shapes in
periods of seven days—full moon in the second; and when it makes its return again, the first is to half-moon, then it CEASES AT ITS CONJUNCTION WITH THE SUN.”
Philo gives a second witness in On Mating with the Preliminary Studies, XIX (102)…
“For it is said in the Scripture: On the tenth day of this month let each of them take a sheep according to his house; in order that from the tenth, there maybe consecrated to the tenth, that is to Elohim, the sacrifices which have been preserved in the soul, which is illuminated in two portions out of the three, until it is entirely changed in every part, and becomes a heavenly brilliancy like a full moon, at the height of its increase at the end of the second week”.
in vol. 6, chapter 16 of The Stromata, Clement plainly writes that “in periods of seven days the moon undergoes its changes. In the first week she becomes half moon; in the second [week], full moon; and in the third [week], in her wane, again half moon; and in the fourth [week] she disappears.”