A lunisolar calendar whose rules are fixed by arithmetic, so its dates are exact.
The Hebrew calendar is lunisolar, inserting a thirteenth month seven times in a nineteen-year cycle. What distinguishes it from other lunisolar calendars in practice is that the rules were fixed arithmetically in late antiquity rather than left to observation.
That has a direct consequence for anyone holding dates: Hebrew-calendar festivals can be computed exactly, centuries ahead, and this corpus records them as exact rather than as estimates. Hijri dates, computed from a calendar that begins its months on sighting, cannot be.
Two lunar calendars, the same underlying astronomy, and different certainty — because one settled its rules and the other kept the observation.
Both recorded as exact rather than estimated, because the Hebrew calendar's intercalation is arithmetic rather than observational.
| 🇮🇱 | Thursday 22 April 2027Israel | Passover — first dayPrecision: exact. |
| 🇮🇱 | Wednesday 28 April 2027Israel | Passover — seventh dayAlso exact, six days later. |
Both are lunar. The Hebrew calendar's months are fixed by arithmetic and compute exactly; Hijri months begin on a sighting and compute as estimates.
See also lunisolar calendar · hijri calendar · intercalation · precision
We hold this as rule_type: hebrew_date. See what we hold.