# Julian Day

The julian day is a continuous count of days from the beginning of the Julian period; it is used primarily by astronomers, and in software for easily calculating elapsed days between two events (e.g., food production date and expiration date). The Julian period is a chronological interval of 7980 years, derived from three multi-year cycles: the indiction, solar, and lunar cycles. The last year that was simultaneously the beginning of all three cycles was 4713 BC (−4712), so that is year 1 of the current Julian period, making AD 2026 year 6739 of that Period.