A Little History about the Qumran Scrolls
the following excerpt is from https://www.bibliotecapleyades.net/scrolls_deadsea/uncovered/uncovered04.htm
The calendar texts from Qumran Cave 4 are numerous and significant. They comprise eighteen texts (4Q319-330 and 4Q337), not including many which, while not strictly related to a calendar, present a calendar system.
Especially noteworthy is the absence among the Qumran find is any text advocating a different calendar. This absence is important because the calendar found in the Qumran materials was only one of several in use and seems to have represented a minority position. The calendar texts are, therefore, central to any attempt to understand the significance of the Dead Sea Scrolls. In order to follow the rather technical expositions of these texts, one must know a few facts about the calendar they advocate, and about the priestly courses (mishmarot) which served in the Temple at Jerusalem.
The calendar is purely solar, based on a particular understanding of the Creation account found in Genesis. In its exclusive reliance on the sun, it stands in stark contrast to later Rabbinic Judaism, which followed a lunisolar calendar of 354 days relying mainly on the moon. Earlier, the Pharisaic forerunners of Rabbinic Judaism seem to have followed an even more lunar-oriented calendar, though from the evidence of the Qumran texts, the lunisolar calendar seems already to have gained currency during at least some of the period of the Scrolls.
In the system that finally emerged, probably under Greco-Roman influence, in Rabbinic Judaism at the end of the fourth century AD, extra lunar months were intercalated seven times in every nineteen years to produce the kind of harmonization necessary to ensure that the calendar remained fixed to the seasons of the solar cycle. The Muslims, for their part, reflecting probably an earlier phase of this historical process, never made the complicated mathematical and calendrical intercalations necessary for passage from a lunar to a lunisolar calendar.
Although the authors of the Qumran calendrical texts disdained the lunisolar calendar, a number of their writings synchronize the two versions. The reasons for this synchronization are not entirely clear, but they may have found it necessary to be able to point out errors with the current system and to know the correct answers.
The only question that must be asked is whether this calendar goes back to Maccabean times, as the third text on Priestly Courses implies – or even earlier – and whether the Maccabeans themselves preferred it before the Pharisees took over with the rise of Herod once and for all. However this may be, the anti-Pharisaic and consequently, the anti-Herodian character of the calendar cannonot be denied.
The exile of the Zadok order
In 167 BCE, King Antiochus returned to Jerusalem after his second campaign in Egypt, and he immediately banned the Hebrew religion and the Zadok Priestly order, and prohibited all religious practices. He dedicated the Temple in Jerusalem to Zeus, the Lord of Heaven (Baal Shamen), and ordered the Hebrew people to worship Zeus and to participate in the festival honoring Dionysus, who was Zeus’ son, (who was called Bacchus by the Romans), and Dionysus/Bacchus was known as the “dying and rising god” as he was “twice born.” This festival, called Bacchanalia, was held on March 16th and March 17th to pollute the Hebrew Spring Equinox Day and New Year’s Day. When King Antiochus began sacrificing swine and making abominable offerings in the Temple, this began the Maccabean revolt (1 Maccabees Chapter 1, and 2 Maccabees Chapters 4, 6 and 7)
After the death of King Antiochus, in 164 BCE, some of the Hebrew priests tried to restore the Solar Calendar, but the Greek “New Moon” influence was all around them. Later, in 359 CE, Hillel II introduced the fixed calculated New Moon Calendar which is based on the conjunction of the moon, and it is the Lunar Calendar that has been used by Jews and others to this day to determine the 1st Day of the Months and the Annual Feast Days. However, the term “New Moon” (yareach chadash יָרֵחַ חָדָשׁ) ) is not written anywhere in the Hebrew Scriptures.