Date boundaries, rules, sources, license & terms of use
Year-start rule (selectable, experimental): using the approximate astronomical March equinox instant in Jerusalem (Asia/Jerusalem), select either (A) the first Wednesday whose local civil date is strictly later than the equinox date (the original v0.5b rule; an equinox on Wednesday yields the following Wednesday), or (B) the nearest Wednesday by civil-date distance, which can occur before, on, or after the equinox date. In mode B, an equinox on Wednesday selects that Wednesday. The selected rule is applied independently to the start of this year and the next year, including the intercalary-week calculation. Neither rule is asserted as a recovered ancient intercalation instruction.
Next intercalary week forecast: the seven Gregorian dates shown are determined from the selected model, not from a historically established Essene leap-week schedule. Starting with the selected year, the tool calculates successive modeled New Year starts under the current Wednesday rule. When two consecutive starts are 371 days apart, the final seven days before the latter start form the intercalary week. The forecast includes a week within the currently displayed modeled year. Forecasts extending beyond the supported 1900–2100 display range are marked provisional and require independent ephemeris verification.
Structure: twelve months in four quarters of 30, 30 and 31 days; 364 ordinary days. The 31st day of each quarter is marked as a quarter-closing day. Any seven days remaining before the next independently calculated year-start form a separate intercalary week at year-end, under the currently selected year-start rule. No Essene Anno Mundi epoch is assumed.
Moedim: this model includes Passover, Unleavened Bread, barley first fruits (1/26), Shavuot (3/15), new wine (5/3), new oil (6/22), wood offerings (7/23–28), Trumpets (7/1), Atonement (7/10), Sukkot (7/15–21), and the Great Day (7/22). These labels follow a selected Qumran-type festival schedule. Trumpets is one modeled day. Hanukkah and Purim are not included as modeled Torah moedim. Identification of John 7’s “last day” with 7/22 is not decided by the calendar.
Day boundaries: dates printed in each cell refer to the Gregorian daytime. The fixed Hebrew date begins at sunset on the preceding Gregorian date and advances at local sunset. This tool does not calculate sunset times or prescribe an ancient Essene day boundary.
Astronomy: Meeus equinox approximation, including 24 periodic terms and NASA/Espenak–Meeus ΔT correction. Supported years: 1900–2100. Times are approximate; future ΔT and near-midnight cases require ephemeris confirmation. Hebrew dates use the browser’s standard Hebrew-calendar implementation (Intl/ICU), checked against Hebcal.
Moon-phase dashboard: the separate dashboard lists new moon, first quarter, full moon and last quarter during the selected modeled month. In full-year view, select a month heading to open that month and its lunar dashboard. These astronomical phases do not determine the calendar’s month starts, festivals or intercalation. Calculations run offline with Astronomy Engine 2.1.19. Dates and HH:MM times are displayed in Asia/Jerusalem, rounded to the nearest minute, with the UTC offset at each event. When rounding crosses midnight, the displayed date advances accordingly. Icons are conventional phase symbols, not predictions of orientation or visibility. The browser supplies historical and future daylight saving time rules; future rules and ΔT remain subject to revision.
Eclipse dashboard (experimental): predicted solar and lunar eclipses are calculated offline with the bundled Astronomy Engine 2.1.19. “Visible from Jerusalem” is the default; “All eclipses worldwide” includes events even when they cannot be seen from Jerusalem. Solar local visibility and the maximum time for Jerusalem use topocentric calculations at 31.778° N, 35.235° E, elevation approximately 800 m. Lunar visibility is an approximate test of whether the Moon’s center is above the local horizon at any sampled point during the penumbral eclipse (approximately two-minute intervals), and does not model buildings, terrain, weather or the difficulty of observing a penumbral eclipse. Events are assigned to a modeled month by the Jerusalem local civil date of the global eclipse maximum. Where a locally visible solar eclipse is listed, its Jerusalem maximum time is shown separately. All times are approximate and rounded to the nearest minute; historical and future ΔT and time-zone rules introduce uncertainty. Eclipse observations do not determine the modeled year start, month boundaries, observances or intercalation.
Branch provenance: v0.7 builds upon the user-revised v0.6a, originally forked from v0.5b. The earlier baselines remain unchanged, and v0.5c is a separate branch. v0.7 adds the calculated next intercalary-week forecast and retains the selectable year-start rule, lunar phases, and solar/lunar eclipse visibility controls.
GNU General Public License: This tool is distributed under the GNU General Public License, version 3 (GPLv3), or any later version. It may be freely used and shared in its original, unmodified form. The GPL also permits modification and redistribution of modified versions, provided the applicable GPL requirements are followed and modified versions are clearly identified as changed.
As-is distribution: If you redistribute this original version without modification, please preserve the tool, methodology notes, source references, and this license notice together so recipients can understand both the calculation methods and the terms under which the software is provided.
No warranty: This tool is provided without warranty of any kind, to the extent permitted by applicable law. No guarantee is made concerning fitness for a particular purpose, historical accuracy, chronological certainty, or suitability of the calculated results for any specific use.
License text: The complete GNU General Public License version 3 is available from the Free Software Foundation at GNU GPLv3..
Astronomy Engine · NASA lunar phase tables · 1 Enoch 72 · DSS calendrical text, 4Q321 · Johnson’s festival schedule (comparison) · NASA ΔT · Hebcal converter
Bundled lunar calculation library · MIT license
Astronomy Engine 2.1.19, by Don Cross, is bundled unchanged under its MIT license. The calendar remains GPLv3-or-later.
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Copyright (c) 2019-2023 Don Cross <cosinekitty@gmail.com>
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