Sources

1. II Chronicles “II Chronicles 8:13 (YLT) — even by the matter of a day in its day, to cause to ascend according to the command of Moses, on sabbaths, and on new moons, and on appointed seasons, three times in a year--in the feast of unleavened things, and in the feast of weeks, and in the feast of booths.”
2. Easton's Bible Dictionary “Easton's Bible Dictionary: Month — Among the Egyptians the month of thirty days each was in use long before the time of the Exodus, and formed the basis of their calculations. From the time of the institution of the Mosaic law the month among the Jews was lunar. The cycle of religious feasts depended on the moon. The commencement of a month was determined by the observation of the new moon. The number of months in the year was usually twelve (1 Kings 4:7; 1 Chr. 27:1-15); but every third year an additional month (ve-Adar) was inserted, so as to make the months coincide with the seasons. "The H”
3. Introduction “1 Enoch (Book of Enoch), Introduction, section 89: year _into_ three hundred and sixty-four _days_, with the leaders of a thousand, who distinguish between the days, as well as between the four additional ones; which, _as_ conductors, divide the four quarters of the year. 12. These leaders of a thousand are in the midst of the conductors, and the conductors are added each behind his station, and their conductors make the separation. These are the names of the conductors, who separate the four quarters of the year, who are appointed _over them_: Melkel, Helammelak, 13. Meliyal, and Narel. 14. A”
4. Introduction “1 Enoch (Book of Enoch), Introduction, section 77: a flame, when they are opened at their proper periods. 12. When the sun rises in heaven, it goes forth through this fourth gate thirty days, and by the fourth gate in the west of heaven on a level with it descends. 13. During that period the day is lengthened from the day, and the night curtailed from the night for thirty days. And then the day is longer by two parts than the night. 14. The day is precisely ten parts, and the night is eight. 15. The sun[170] goes forth through this fourth gate, and sets in it, and turns to the fifth gate durin”
5. Introduction “1 Enoch (Book of Enoch), Introduction, section 81: belonging to the sun in five years; all the days belonging to each year of the five years, when completed, amount to three hundred and sixty-four days; and to the sun and stars belong six days; six days in each of the five years; _thus_ thirty days belong to them; 12. So that the moon has thirty days less than the sun and stars. 13. The moon brings on all the years exactly, that their stations may come neither too forwards nor too backwards a single day; but that the years may be changed with correct precision in three hundred and sixty-four d”
6. Introduction “1 Enoch (Book of Enoch), Introduction, section 88: I given to thee, to thy children, and thy posterity, that they may transmit to their children, for generations for ever, this wisdom in their thoughts; and that those who comprehend _it_ may not slumber, but hear with their ears; that they may learn this wisdom, and be deemed worthy of eating _this_ wholesome food. 4. Blessed are all the righteous; blessed all who walk in _the paths of_ righteousness; in whom no crime _is found_, as in sinners, when all their days are numbered. 5. With respect to the progress of the sun in heaven, it enters an”
7. Introduction “1 Enoch (Book of Enoch), Introduction, section 86: and every week. _He showed me_ also the decrease of the moon, which is effected in the sixth gate; for in that sixth gate is its light consumed. 3. From this is the beginning of the month; and its decrease is effected in the sixth gate in its period, until a hundred and seventy-seven days are completed; according to the mode of computation by weeks,[183] twenty-five _weeks_ and two days. 4. _Its period_ is less than that of the sun, according to the ordinance of the stars, by five days in one half year[184] precisely. 5. When that _their_ visi”
8. Mishneh Torah (Maimonides) (Jewish (Rabbinic)) “Mishneh Torah (Maimonides), Mishneh Torah%2C Sanctification of the New Month 5:13: The calculations that we follow in the present era, every individual in his community, to ascertain which day is Rosh Chodesh and which day is Rosh HaShanah, do not determine [the calendar], nor do we rely on these calculations. For we do not institute leap years or establish the monthly calendar in the diaspora. We rely on the calculations of the inhabitants of Eretz Yisrael and their establishment of the calendar. The reason we make calculations is merely for the sake of information. For we know that the inhab”
9. Sefaria (Jewish (Rationalist)) “Abraham Ibn Ezra on Leviticus 23:4: Scripture then mentions the festivals (v. 4). The Torah says, even these are My appointed seasons , with regard to the Sabbath and in their appointed season with regard to the festivals. The meaning of in their appointed season is, in any day of the week in which they fall. Note, I will now lay down a general rule with regard to the festivals. During the time of the Temple the festivals were in the hands of the Beth Din. Do you not see that Scripture says, For the king had taken counsel (II Chron. 30:2), with regard to the Passover proclaimed by Hezekiah. 3 ”
10. Sefaria (Jewish (Rationalist)) “Abraham Ibn Ezra on Exodus 12:2: THIS MONTH. Rabbi Judah Ha-Parsi 9 One of the early Karaites. He taught that the festivals are to be established in accordance with a solar calendar. It is interesting to note that I.E. uses the title Rabbi in introducing Judah Ha-Parsi. However, in chapter 1 of his Iggeret Ha-Shabbat he quotes the same opinion and there writes, Judah Ha-Parsi says. Similarly, the Karaite Joshua is sometimes quoted with the title Rabbi. As much as one might want to attribute modern notions of civility to I.E., the probability is that the title Rabbi was added by scribes who wer”