Lunar Phase & Illumination Visualizer
Jean Meeus, Astronomical Algorithms 2nd ed. Chapter 49 (Phases of the Moon)
Illumination = (1 - cos(2π · Phase)) / 2
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77% Cycle
Last Quarter
44.1% Illuminated
Visible fraction of the lunar disc facing Earth
0% (New)50% (Quarter)100% (Full)
Moon Age22.7 daysin 29.53d synodic cycle
Phase Angle (k)276.8°geometric elongation
Astronomical Algorithm Note: Moon phases are governed by the synodic month (mean length: 29.53058867 days). Phase zero corresponds to the conjunction of the Moon and Sun (New Moon), while phase 0.50 denotes the exact opposition (Full Moon).
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