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Moon Phase Calculator
Calculate the moon phase, illumination percentage, age, and lunar cycle progress for any date with a visual display.
Moon Phase
Select a date to calculate the moon phase
How to Use
- Select a date — Use the date picker to choose any date past or future.
- Click "Today" — Jump back to the current date's moon phase instantly.
- View results — See the phase name, visual moon rendering, illumination %, moon age, and lunar cycle progress.
- Upcoming phases — Check next and previous new moon and full moon dates.
About Moon Phases
🌑 New Moon
The moon is between Earth and the Sun. The side facing Earth is not illuminated, making the moon invisible from Earth. This marks the start of a new lunar cycle.
🌒 Waxing Crescent
A thin sliver of the moon becomes visible as it moves away from the Sun. The illuminated portion grows each night. This phase is often visible in the western sky after sunset.
🌓 First Quarter
Half of the moon's visible surface is illuminated. The moon has completed about one quarter of its orbit around Earth. It rises around noon and sets around midnight.
🌔 Waxing Gibbous
More than half of the moon is illuminated, but it is not yet full. The moon appears bright and large in the sky. This phase leads up to the full moon.
🌕 Full Moon
Earth is between the Sun and the Moon. The entire face of the moon is illuminated. Full moons occur roughly every 29.5 days and have been given various cultural names (Harvest Moon, Blue Moon, etc.).
🌖 Waning Gibbous
After the full moon, the illuminated portion begins to shrink. The moon rises later each night. This phase is visible in the morning sky.
🌗 Last Quarter
Again half of the moon is illuminated, but the opposite side from the First Quarter. The moon rises around midnight and sets around noon. Also called the Third Quarter.
🌘 Waning Crescent
A thin crescent of the moon is visible just before sunrise. The illuminated portion continues to shrink until the next new moon, completing the 29.5-day cycle.
Frequently Asked Questions
How accurate is the moon phase calculation?
The calculator uses a high-precision algorithm based on the known new moon of January 6, 2000 (JDN 2451550.1). It is accurate to within a few hours for dates within several centuries.
What is the moon's age?
The moon's age is the number of days since the last new moon. It ranges from 0 (new moon) to approximately 29.5 (just before the next new moon).
What is a synodic month?
A synodic month is the time it takes the moon to return to the same phase (e.g., new moon to new moon). It averages 29 days, 12 hours, 44 minutes, and 3 seconds.
What is a Blue Moon?
A Blue Moon is the second full moon occurring within a single calendar month. This happens approximately once every 2.5 years. The term "once in a blue moon" refers to its rarity.
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