Moon Phase Calculator

How the Moon Phase Calculator Works

The moon phase calculator determines the lunar phase for any date by calculating how many days have elapsed since a known new moon and expressing that as a position in the 29.53-day lunar cycle. The synodic period of the moon (new moon to new moon) is exactly 29.530589 days. The algorithm uses Julian Day Numbers for precise date calculations and maps the elapsed fraction of the cycle to the corresponding phase.

The moon completes one full cycle — from new moon through all phases back to new moon — in approximately 29 days, 12 hours, 44 minutes. This is the synodic month (Earth-relative cycle). The sidereal month (orbit relative to stars) is shorter at 27.3 days, but we see phases based on the synodic month because Earth is also orbiting the Sun.

Moon Phases Today: The 8 Lunar Phases Explained

The complete lunar cycle in order:

• 🌑 New Moon (Day 0): Moon is between Earth and Sun; the side facing Earth receives no sunlight. Moon rises and sets with the sun — invisible at night. Duration of "new moon" phase: approximately 1–2 days.
• 🌒 Waxing Crescent (Days 1–7): A sliver of the right side of the moon is illuminated (in the Northern Hemisphere). Crescent visible in the western sky after sunset.
• 🌓 First Quarter (Day 7–8): Exactly half the moon is illuminated (right side). Rises around noon, sets around midnight. The moon is 90° from the Sun.
• 🌔 Waxing Gibbous (Days 8–14): More than half illuminated, growing toward full. "Gibbous" means hump-shaped.
• 🌕 Full Moon (Day 14–15): Entire visible face illuminated. Rises near sunset, sets near sunrise. 180° from the Sun — on the opposite side of Earth from the Sun.
• 🌖 Waning Gibbous (Days 15–22): Begins to shrink from full. Rises after sunset, sets after sunrise.
• 🌗 Last Quarter (Day 22): Half illuminated on the left side. Rises around midnight, visible in morning sky.
• 🌘 Waning Crescent (Days 22–29): Shrinking crescent on the left side. Visible in eastern sky before dawn. Returns to new moon.

Full Moon Calendar 2025–2026

Upcoming full moon dates and their traditional names:

• May 12, 2025 — Flower Moon
• June 11, 2025 — Strawberry Moon
• July 10, 2025 — Buck Moon
• August 9, 2025 — Sturgeon Moon
• September 7, 2025 — Harvest Moon
• October 6, 2025 — Hunter's Moon
• November 5, 2025 — Beaver Moon
• December 4, 2025 — Cold Moon
• January 3, 2026 — Wolf Moon
• February 1, 2026 — Snow Moon
• March 3, 2026 — Worm Moon
• April 2, 2026 — Pink Moon

Traditional moon names originated from Native American tribes and colonial American settlers who tracked seasons by the lunar calendar. The Harvest Moon (closest full moon to the autumnal equinox) is distinctive because it rises nearly at sunset for several consecutive nights, historically extending farming daylight into the evening.

Lunar Phase Calendar: Moon Phase Effects and Folklore

The moon's phases have influenced human culture, agriculture, and fishing for millennia:

• Tides: Full and new moons create spring tides (higher high tides and lower low tides) due to gravitational alignment of Sun, Earth, and Moon. First and last quarter moons create weaker neap tides. This is one of the moon's most measurable effects on Earth.
• Fishing: Many anglers follow solunar tables (developed by John Alden Knight in 1936) which predict peak fish feeding times based on moon position. New and full moons are associated with the best fishing by many practitioners.
• Gardening: Biodynamic agriculture practices planting root crops during waning moon phases and leafy crops during waxing phases. Scientific evidence is limited but the practice is widespread in traditional farming communities.
• Emergency medicine: Studies have found no statistically significant relationship between full moon phases and emergency room visits, psychiatric admissions, or human birth rates — despite widespread belief in these effects (the "lunar effect" myth).

Frequently Asked Questions

What is a supermoon?

A supermoon occurs when a full moon (or new moon) coincides with the moon's closest approach to Earth in its elliptical orbit (perigee). At perigee, the moon is about 14% larger in apparent diameter and 30% brighter than at apogee (farthest point). The term "supermoon" was coined by astrologer Richard Nolle in 1979 and popularized in recent decades. A full moon within 90% of perigee is typically called a supermoon; there are usually 3–4 per year.

What is a blue moon?

A "blue moon" has two common definitions: (1) The third full moon in a season that has four full moons (traditional definition), occurring approximately every 2.7 years. (2) The second full moon in a calendar month (modern popular definition). The phrase "once in a blue moon" comes from how rare it is — roughly 12–13 times per century. Despite the name, the moon doesn't actually appear blue (though lunar hazes from atmospheric particles like smoke can occasionally give the moon a blue tint).

Why do we always see the same side of the moon?

The moon is tidally locked to Earth — it rotates once on its own axis in exactly the same time it takes to orbit Earth (about 27.3 days). This synchronous rotation means the same hemisphere always faces Earth. We see only about 59% of the lunar surface (due to libration — slight wobbling in the moon's orbit), but we never see the far side from Earth. The far side was first photographed in 1959 by the Soviet Luna 3 spacecraft.