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The Solar Hijri calendar is arguably the most accurate solar calendar in human history. It does not drift against seasons—Nowruz always marks the first day of spring. In contrast, the Gregorian calendar accumulates a 1-day drift every 3,333 years, requiring eventual correction.

The Solar Hijri year typically begins on the vernal equinox (March 19, 20, or 21).

for global historiography.