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The Moon returns to the same phase every 29.53059 days (synodic month). Phase is calculated from the angle between Sun and Moon as seen from Earth.
Phase angle = (Moon longitude − Sun longitude) mod 360°Illuminated fraction equals (1 − cos(phase angle)) / 2. New moon = 0%, first/last quarter = 50%, full moon = 100%.
Illumination = (1 − cos(θ)) / 2 × 100%Next new or full moon occurs when phase angle crosses 0° or 180°. Calculated by advancing time in fractional-day steps from the current ephemeris position.
Updated: July 2026
New moon window: five days before to three days after new moon for darkest skies. Calculator shows next new moon in 8 days — schedule imaging session accordingly.
Tonight 78% illuminated waxing gibbous. Terminator shadow reveals crater detail along the western limb. Best imaging within 2 hours of sunset while Moon is low and stable.
Spring tides occur around new and full moon (±2 days). Next full moon in 5 days — expect higher high tides and stronger current for surf fishing.
Full moon rises at sunset and sets at sunrise. First quarter rises at noon and sets at midnight. Phase determines rise time, not just brightness.
A 70%+ illuminated moon washes out the Milky Way and faint nebulae. Shoot within the 7-day window centered on new moon for best results.
The Moon cycles through phases every 29.5 days, affecting night sky brightness, tides, and visibility of faint deep-sky objects. This calculator shows the current phase, illumination fraction, and upcoming new and full moon dates for any date.