Moon Phase Calculator – Check Moon Phases Free Online

Moon Phase Calculator: Essentials & Use Cases

The phases of the Moon are the different ways the Moon looks from Earth over about a month. As the Moon orbits our planet, the Sun lights up different parts of it, creating the familiar cycle from New Moon to Full Moon and back again. Our Moon Phase Calculator uses precise astronomical algorithms to determine the exact lunar phase, illumination percentage, and age of the Moon for any given date.

• Track Lunar Cycles: Effortlessly follow the Moon’s journey through its eight distinct phases.
• Plan Your Activities: Schedule gardening, fishing trips, spiritual rituals, or astrophotography sessions to align with the perfect lunar conditions.
• Powerful Educational Tool: Enhance lessons in astronomy, history, and even biology by providing accurate, real-time lunar data.

Core Moon Phase Calculation Details

The Eight Phases of the Moon: A Detailed Guide

The lunar cycle is a beautiful and continuous process, but we traditionally divide it into eight distinct phases. These are determined by the angle of the Moon relative to the Earth and Sun. The terms “waxing” mean the illuminated portion is growing, while “waning” means it is shrinking. Our Moon Phase Calculator can instantly tell you which of these phases occurs on any day.

1. 1. New Moon

   The cycle begins with the New Moon. At this phase, the Moon is positioned between the Earth and the Sun. The side of the Moon facing us is not illuminated by the Sun (except for a faint glow of reflected “earthshine”). It is invisible in the sky and rises and sets with the Sun. The Moon’s age is 0 days, and its illumination is near 0%.

2. 2. Waxing Crescent

   A few days after the New Moon, a sliver of the Moon becomes visible. This is the Waxing Crescent. “Waxing” means it is growing larger. This slender crescent is visible in the western sky shortly after sunset.

3. 3. First Quarter

   About a week into the cycle, the Moon reaches its First Quarter. It appears as a “half-moon.” From our perspective, the right half of the Moon is illuminated. It is called a “quarter” phase because the Moon has completed one-quarter of its orbit around the Earth.

4. 4. Waxing Gibbous

   Following the First Quarter, the illuminated portion continues to grow. A shape that is more than half but not yet full is called “gibbous.” The Waxing Gibbous moon is prominent in the night sky, setting after midnight.

5. 5. Full Moon

   This is the most spectacular phase. The Earth is positioned between the Sun and the Moon, so the entire side of the Moon facing us is illuminated. The Full Moon rises at sunset and sets at sunrise, dominating the sky all night long. Its illumination is 100%, and its age is roughly 14.8 days.

6. 6. Waning Gibbous

   After the peak of the Full Moon, the illuminated portion begins to decrease, or “wane.” The Waning Gibbous moon rises after sunset and is visible for much of the night and into the early morning.

7. 7. Third Quarter (or Last Quarter)

   About three weeks into the cycle, the Moon reaches its Third Quarter. It once again appears as a “half-moon,” but this time it’s the left half that is illuminated. It has now completed three-quarters of its orbit.

8. 8. Waning Crescent

   In the final days of the cycle, the Moon is reduced to a thin sliver again. This Waning Crescent is visible in the eastern sky just before sunrise, heralding the return of the New Moon.

The Science of the Lunar Cycle: Sidereal vs. Synodic Months

The rhythm of the Moon’s phases is governed by its orbit around the Earth. However, there are two different ways to measure a lunar month, and understanding them is key to how a Moon Phase Calculator works. The apparent motion of the Sun plays a crucial role.

The Sidereal Month: Orbiting the Earth

The sidereal month is the time it takes for the Moon to complete one full orbit around the Earth with respect to the distant stars. If you were to watch the Moon from a vantage point far out in space, this is the orbital period you would measure. A sidereal month is approximately 27.3 days long.

The Synodic Month: The Cycle of Phases

The synodic month is the time it takes for the Moon to return to the same phase as seen from Earth (e.g., from one New Moon to the next). This is the cycle that governs our experience of the lunar phases. A synodic month is approximately 29.53 days long—more than two days longer than a sidereal month.

Why the Difference?

The difference exists because as the Moon orbits the Earth, the Earth-Moon system is also orbiting the Sun. In the 27.3 days it takes the Moon to complete one orbit around the Earth (sidereal month), the Earth has moved about 1/12th of the way in its own orbit around the Sun. Because of this, the Moon must travel a little further in its orbit—an extra two days or so—to “catch up” and get back to the same alignment with the Sun and Earth that defines a specific phase (like the New Moon).

All lunar calendars and any accurate moon phase calculator must use the synodic period of 29.530588853 days to correctly predict the phases.

The Moon in Culture, Folklore, and Practical Life

For millennia, before the invention of clocks and modern calendars, the Moon was humanity’s primary timekeeper. Its predictable cycle provided a rhythm for hunting, planting, and gathering. The Full Moon, in particular, has always held a special significance, often being given names by various cultures based on the activities of that season. A Moon Phase Calculator can help you connect with these ancient traditions by identifying these special moons.

Traditional Full Moon Names

Many of the common Full Moon names used today come from Native American tribes, particularly the Algonquin, as well as from Anglo-Saxon and Germanic traditions. These names reflect the natural events of the seasons.

• January: Wolf Moon – Named for the howling of wolves that were often heard during this cold winter month.
• February: Snow Moon – Named for the heavy snows that typically fall in February.
• March: Worm Moon – As the ground began to thaw, earthworm casts would appear, heralding the return of robins.
• April: Pink Moon – Named for the early springtime blooms of a certain wildflower, wild ground phlox, also known as “moss pink.”
• May: Flower Moon – Named for the abundance of flowers that bloomed in May.
• June: Strawberry Moon – Marked the short season for harvesting strawberries.
• July: Buck Moon – Named for when the new antlers of buck deer emerge from their foreheads.
• August: Sturgeon Moon – Named by fishing tribes who knew this was the best time to catch sturgeon.
• September: Harvest Moon – The Full Moon closest to the autumnal equinox. The bright moonlight allowed farmers to work late into the night to harvest their crops.
• October: Hunter’s Moon – The month for hunting and laying in stores for the long winter ahead.
• November: Beaver Moon – Marked the time to set beaver traps before the swamps froze, to ensure a supply of warm winter furs.
• December: Cold Moon – Named for the arrival of deep winter and its long, cold nights.

Blue Moons and Supermoons

A “Blue Moon” is not actually blue in color. The term most commonly refers to the second Full Moon that occurs within a single calendar month. Because the lunar cycle is about 29.5 days, this happens roughly once every 2.7 years. A “Supermoon” occurs when a Full Moon coincides with the Moon’s perigee—the point in its elliptical orbit when it is closest to Earth. This makes the Moon appear slightly larger and brighter than usual.

The Connection Between Moon Phases and Eclipses

Solar and lunar eclipses are spectacular celestial events that are directly tied to the phases of the Moon. An eclipse can only happen when the Sun, Earth, and Moon are perfectly aligned in a straight line, an alignment known as a “syzygy.” This perfect alignment is only possible during two specific moon phases.

Solar Eclipses and the New Moon

A solar eclipse occurs when the Moon passes directly between the Sun and Earth, and the Moon’s shadow is cast upon the Earth. This can only happen during the New Moon phase, which is the only time the Moon is in the correct position between the other two bodies. An observer in the path of the Moon’s umbra (the darkest part of the shadow) will see a total eclipse, where the Sun is completely blocked. Observers in the penumbra (the lighter part of the shadow) will see a partial eclipse.

Lunar Eclipses and the Full Moon

A lunar eclipse occurs when the Earth passes directly between the Sun and Moon, and the Earth’s shadow is cast upon the Moon. This can only happen during the Full Moon phase, when the Moon is on the opposite side of the Earth from the Sun. As the Moon passes through the Earth’s umbra, it often takes on a reddish glow, a phenomenon that gives it the nickname “Blood Moon.” This is because some sunlight is filtered and refracted through Earth’s atmosphere and then projected onto the Moon.

Why Don’t We Have Eclipses Every Month?

If a solar eclipse requires a New Moon and a lunar eclipse requires a Full Moon, why don’t they happen every two weeks? The reason is that the Moon’s orbit around the Earth is tilted by about 5 degrees with respect to the Earth’s orbit around the Sun (the ecliptic plane). Because of this tilt, the Moon’s shadow usually passes either above or below the Earth during a New Moon, and the Moon usually passes above or below the Earth’s shadow during a Full Moon. Eclipses only occur during the two “eclipse seasons” each year when the line of intersection of these two orbital planes points toward the Sun.