Precise daily moon phases, illumination percentages, and phase names for any month from 1900–2100. Based on astronomical algorithms (mean lunar cycle). Click any date for detailed phase info.
October 5, 2025
Illumination: 97%
Distance: 384,400 km
Moon Age: 14.8 days
The moon goes through a cycle of phases each month as it orbits Earth. This cycle takes about 29.5 days to complete, known as a lunar month.
0% illuminated
The moon is between Earth and the Sun1-49% illuminated
Growing crescent after new moon50% illuminated
Right half of moon is visible51-99% illuminated
Growing after first quarter100% illuminated
Entire moon is visible99-51% illuminated
Shrinking after full moon50% illuminated
Left half of moon is visible49-1% illuminated
Shrinking crescent before new moonLunar Cycle: The moon completes its orbit around Earth in approximately 27.3 days (sidereal month), but due to Earth's movement around the Sun, the cycle of phases (synodic month) takes about 29.5 days.
Moon's Influence: The moon affects ocean tides, animal behavior, and has been used for timekeeping throughout human history.
The Moon Phase Calendar displays the changing appearance of the Moon as seen from Earth. These phases arise from the relative positions of the Moon, Earth, and Sun. A full lunar cycle (synodic month) lasts approximately 29.53059 days. Our calculator uses a high-precision mean lunar cycle algorithm referenced to a known new moon epoch (J2000.0), giving reliable phase angles and illumination fractions within ±0.5° accuracy for most historical and future dates.
Phase Angle θ = 360° × (ΔT / 29.530588853) mod 360,
Illumination k = (1 − cos θ) / 2.
The algorithm uses a reference new moon on January 6, 2000, at 18:14 UTC (JD 2451549.5). This epoch corresponds to the J2000.0 standard astronomical reference frame, which is the IAU-adopted reference for celestial coordinates and ephemerides beginning at 12:00 TT (Terrestrial Time) on January 1, 2000. The mean synodic month length is taken as 29.530588853 days, consistent with the IAU standards. The illumination fraction is derived from the phase angle (θ) via the cosine law: illumination = (1 + cos θ)/2 (where θ=0° = new, θ=180° = full). This matches geometric visibility of the Moon's disk. For a given date, we compute the exact days since reference epoch and derive the phase. The calendar provides daily values at 00:00 UTC (convertible to local time). The error is negligible for educational and practical purposes.
Limitations of mean model: The algorithm uses the mean synodic month. Actual moon phases vary by up to ±0.25 day due to orbital eccentricity and perturbations (e.g., evection, variation). The two most significant perturbations are Evection (caused by solar gravitational influence on the Moon's elliptical orbit, producing ±1.3° variation in mean anomaly) and Variation (a periodic change in the Moon's mean longitude with amplitude of ±40'). Additional factors include the annual equation, parallactic inequality, and planetary perturbations. For precise astronomical events (eclipses, supermoons, lunar standstills), refer to NASA's Horizons system or professional ephemerides. This tool is intended for general planning, education, cultural, and religious uses.
Ocean tides are primarily driven by the Moon's gravitational pull. Spring tides (higher high tides) occur during new and full moons, when the Sun, Moon, and Earth align. Neap tides (lower tidal range) occur during first and third quarters. Mariners and coastal engineers rely on lunar phase predictions for navigation and construction schedules.
Many ancient civilizations—Babylonian, Mayan, Chinese, and Hindu—based their calendars on lunar months. The word "month" derives from "moon". In modern times, moon phases remain essential for Islamic calendar (Hijri), Jewish calendar (Rosh Chodesh), and Tibetan lunar calendar. For example, the Islamic calendar (Hijri) is purely lunar, with months beginning upon the first verified sighting of the waxing crescent moon after astronomical conjunction. Our tool's crescent phase predictions help understand the approximate timing of such religious observations, though actual declarations depend on local crescent visibility committees. Our tool bridges ancient wisdom and modern computational astronomy.