Moon Phase Calculator — Plan Night Sky Photography
Calculate moon illumination and phase for any date to plan your astrophotography sessions.
How We Calculate This
The moon completes a full cycle (new moon to new moon) in approximately 29.53 days, known as the synodic month.
Moon age = (days since reference new moon) mod 29.53
Illumination = (1 - cos(age / 29.53 × 2π)) / 2 × 100%
The eight standard phases are determined by dividing the cycle into equal segments. The reference new moon used is 6 January 2000 at 18:14 UTC.
Frequently Asked Questions
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Last updated: February 2026
All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.