What did Second Temple Judaism think about the calendar?

By the Second Temple period (roughly 516 BC – AD 70), the calendar question had become a sectarian flashpoint inside Judaism. Two streams of literature survive that bear on the question, and they pull in opposite directions. Both are non-canonical; their value here is as historical witnesses to what Second Temple Jews actually believed about calendar.

Stream 1: pseudepigraphal — the 364-day polemic.

The pseudepigraphal works are texts attributed to ancient figures (Enoch, Moses, the Patriarchs) but composed in the Second Temple period. They are not part of any extant canon — Protestant, Catholic, Orthodox, or Jewish. They are valuable as evidence of what one party believed.

1 Enoch 72–82, the so-called "Astronomical Book" or "Book of the Heavenly Luminaries," sets out a calendar of 364 days. The system is twelve months of 30 days each (= 360) plus four intercalary days inserted at the equinoxes and solstices (= 364). 1 Enoch 72:32 specifies the structure; 1 Enoch 80 makes calendar disorder a sign of the eschatological period of disobedience:

"And in those days many will turn away from the path of righteousness and will commit all manner of evil ... and the moon will alter its order and not appear at its proper times. And in those days many heads of the stars will go astray from the command and these will alter their courses..."

— 1 Enoch 80 (pseudepigraphal)

The argument is polemical: lunar disorder is sinful disorder. The solar 364-day calendar is pure; the moon is unreliable.

Jubilees 6:30–38 declares the 364-day calendar engraved on the heavenly tablets and explicitly attacks lunar reckoning:

"All the days of the commandment will be fifty-two weeks of days, and they will make the entire year complete... There will be no neglecting (this commandment) for a single year or from year to year. And command the children of Israel that they observe the years according to this reckoning — three hundred and sixty-four days, and (these) will constitute a complete year, and they will not disturb its time from its days and from its feasts. ... For there will be those who will examine the moon diligently because it will corrupt the (appointed) times and it will advance from year to year ten days. ... And they will set awry the months and the appointed times and the sabbaths and the feasts."

— Jubilees 6:30–38 (pseudepigraphal)

Notice what the polemic concedes even as it attacks: lunar reckoning advances from year to year ten days. That is precisely the ~11-day drift of a pure 354-day lunar year against the solar cycle — and the very problem that mainstream Second Temple Judaism solved by intercalation. The Jubilees author is arguing against a calendar that uses lunar months and adjusts them — i.e., a luni-solar calendar — and the workaround he proposes is a fixed 364-day solar year.

The Qumran calendrical scrolls (4Q319, 4Q320–4Q330, 4Q252) follow the same 364-day system — separate manuscripts well-attested in the secondary literature. The Qumran community (often identified with the Essenes, but the identification is debated) treated the Hasmonean-Pharisaic luni-solar calendar as illegitimate and observed the 364-day calendar internally. The polemic was sectarian — and it was a polemic against the mainstream, not the mainstream itself.

Stream 2: deuterocanonical — the luni-solar mainstream.

The deuterocanonical works (canonical for Catholic and Orthodox Christians; not canonical for Jews or Protestants) are valuable here as witnesses to the calendrical assumptions of mainstream Greek-speaking Jewish writers in the Hellenistic and early Roman period. They consistently assume the luni-solar system the canonical Old Testament prescribes.

Sirach 43:6–8 (composed ~180 BC, translated into Greek by the author's grandson ~132 BC) explicitly etymologizes μήν ("month") from σελήνη ("moon") and names the moon as the festival anchor:

"And the moon — in all things at her season, an indicator of times and an everlasting sign. From the moon is the sign of the feast (ἀπὸ σελήνης σημεῖον ἑορτῆς), a light that wanes when she completes her course."

— Sirach 43:6–7 (deuterocanonical, LXX_Sir)

Sirach 33:7 adds: "Why does day excel day, when all the light of every day in the year is from the sun?" — pairing the lunar month with the solar year exactly as Genesis 1:14 does. Sirach 50:6 figures the high priest at the temple as a "full moon" (σελήνη πλήρης) — the simile is dead unless the lunar month is the festival anchor.

Wisdom of Solomon 7:18–19 (a Greek Jewish text from ~50 BC – AD 50) pairs eniautou kuklous ("cycles of the year") with tropai ("solstices") — luni-solar phenomena reported together as part of Solomon's wisdom about creation.

Tobit 2:1 dates the celebration of Pentecost (πεντηκοστή) by the seven-week count from Passover — a lunar-anchored festival counted across seven weeks of weeks (cf. Lev 23:15–16, MT). The seven-week reckoning is luni-solar, not 364-day.

1 Maccabees — the Hasmonean court history covering 175–134 BC — uses Babylonian-derived lunar month names (Χασελευ = Kislev) and dates the rededication of the temple by them: "on the twenty-fifth day of the ninth month, which is the month of Chislev" (1Ma 4:52, deuterocanonical). The Hasmonean priesthood that restored the temple after the Maccabean revolt operated on the luni-solar calendar — the same priesthood whose calendar Jubilees and the Qumran scrolls attack.

The polemical asymmetry is itself the evidence.

This is the structural point. 1 Enoch and Jubilees are polemical works. They are arguing for the 364-day calendar against something. What they are arguing against is the existing mainstream — and that mainstream is consistently described, in their own complaints, as lunar-based with periodic adjustment (the very ~10-day-per-year drift Jubilees 6:36 names). That is exactly the canonical luni-solar system Torah's Aviv-statute requires. The fact that 1 Enoch and Jubilees had to be written at all is evidence that mainstream Second Temple Judaism was luni-solar.

If the canonical Old Testament had taught a 360-day or a 364-day calendar, no polemic would have been needed. The 364-day texts are reformist — they are trying to change something. What they are trying to change is the calendar of the temple itself.

The 360-day calendar appears in neither stream.

This is the part that surprises modern readers most. The popular "prophetic 360-day year" is not the position of any known Second Temple Jewish group. No surviving Second Temple text — pseudepigraphal, deuterocanonical, Qumran sectarian, or rabbinic — follows a 360-day calendar. The sectarian alternative was 364, not 360. The mainstream was luni-solar. The 360 figure exists only in the symbolic arithmetic of Revelation, where it interlocks 42 months × 30 days = 1,260 days = "time, times, and half a time" — internal apocalyptic stylization, not a calendar Second Temple Judaism observed.

What this implies for reading the canon.

Three reading consequences:

1. The luni-solar system is not a "later Jewish tradition" imposed on Torah after the exile. It is the system Torah's own vocabulary names — Aviv (H24, the agricultural anchor), chodesh (H2320, the lunar month), teqūfat ha-shanah (H8622, the solar circuit) — and the system the deuterocanonical stream takes for granted as ancestral.
2. The 364-day calendar is a sectarian protest against mainstream luni-solar reckoning, not the canonical position. Reading 1 Enoch or Jubilees as evidence for the canonical Old Testament's calendar inverts the polemic — the texts are opposing the canonical mainstream, not preserving it.
3. The 360-day calendar is not a Second Temple position at all. It is a stylized number internal to Revelation's apocalyptic equation. To project it back onto Daniel as the calendar Daniel assumed is to put on Daniel an arithmetic that no Jewish group of his presumed era — or any subsequent era — actually used.

For the full lexical analysis of the canonical year-vocabulary and the calendar Torah's Aviv-statute legislates, see What Is a Year in the Bible?. For the deuterocanonical and pseudepigraphal status of the works cited here, and how the canon weighs them, see the project's standing convention: deuterocanonical and pseudepigraphal texts are valuable as historical witnesses to Second Temple belief, but are not doctrinally authoritative on the same level as canonical Scripture.