Astronomy & Earth Science
Moon Phase Calculator
Lets users compute and verify moon phase instantly with formula, steps and examples — no manual math.
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Your result
Moon phase
New Moon
Moon age 28.7 days → New Moon, 1% illuminated.
Illumination
0.71%
Moon age
28.7377 days
About this calculator
Computes the Moon's phase from its age in the 29.53-day synodic cycle, measured from a reference new moon (Jan 6, 2000). Illumination follows (1 − cos(2π·age/period))/2. Times are approximate (±1 day) and not location-adjusted.
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