A lunar year runs about eleven days short of a solar one. Watch what that does over time — why Passover would slide out of spring if nobody stopped it, why the Hebrew calendar yanks it back and the Islamic calendar lets it wander, and how the same machinery bears on a two-thousand-year-old argument about a Friday in April.
Every gospel puts the death on a Friday, before the Sabbath, during Pilate's prefecture (AD 26–36 — the one point all four gospels and Tacitus agree on). The gospels then disagree on which Friday: John has the death on 14 Nisan, as the Passover lambs were killed; the synoptics imply 15 Nisan. Pick a rule and search — the engine reconstructs each year's Nisan from the moon and tells you the weekday.
The calendar alone allows more than two Fridays in this window. Scholars narrow it to AD 30 and AD 33 using non-calendrical evidence — the length of Jesus's ministry and John the Baptist starting in Tiberius's 15th year. This tool only does the astronomy; the rest is history's job.
| Year | Nisan 14 | Weekday | Notes |
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The Metonic leap-year pattern this dial animates (years 3, 6, 8, 11, 14, 17, 19) is the modern one. The Encyclopaedia Judaica records rival intercalation sequences still in use as late as the 10th century — (1,4,6,9,12,15,17), (3,5,8,11,14,16,19), (2,5,7,10,13,16,18). Which pattern first-century Judea used is not settled. The wheel you're watching is one reconstruction among several.
The engine computes the astronomical new moon (conjunction) to the minute. But a month began when the crescent was first seen, one to two evenings later, depending on weather and geometry. That gap is modelled here by a crude age-at-sunset rule. Move the slider and dates shift — because the real answer genuinely shifts with the model.
A partial lunar eclipse rose over Jerusalem near 6:20 pm on 3 April AD 33 — the moon already reddened — and it was the only one visible at Passover across AD 26–36. Humphreys & Waddington tie it to "the moon turned to blood" (Acts 2:20). It's suggestive and popular. Others read that verse as apocalyptic imagery, not an eyewitness eclipse. Weigh it, don't lean on it.
The drift you see in Islamic mode follows from abolishing intercalation (nasī') per Qur'an 9:36–37, proclaimed at the Farewell Pilgrimage. But if nasī' did mean intercalation, some early-Islamic event dates (the Hijra, Badr, Uhud) could themselves be off by one to three lunar months. Lunar dating is slippery on both sides of this instrument.