Moon Phase Today — Lunar Phase Tracker
The current moon phase is Waning Gibbous with 50% illumination (at build time). The tracker below updates in real time.
| Illumination | 50% |
| Moon Age | 22.1 days |
| Phase Name | Waning Gibbous |
| Days until Full Moon | 22.2 days |
| Lunation Period | 29.53 days |
Understanding Lunar Phases
The Moon does not produce its own light. What we perceive as moonlight is sunlight reflecting off the lunar surface. As the Moon orbits Earth over the course of approximately 29.53 days, the angle between the Sun, Earth, and Moon changes continuously, causing the illuminated portion visible from Earth to shift in a predictable pattern. This cycle of changing appearances is what we call the lunar phases.
There are eight principal phases recognized in modern astronomy. The cycle begins with the New Moon, when the Moon sits between Earth and the Sun and its sunlit hemisphere faces entirely away from us. The Moon is essentially invisible during this phase, lost in the Sun's glare. Within a day or two, a thin sliver of light appears on the right side (in the Northern Hemisphere), marking the start of the Waxing Crescent phase. The word "waxing" means growing, and each evening the illuminated portion expands.
About a week after the New Moon, exactly half of the Moon's visible face is illuminated. This is the First Quarter, so named because the Moon has completed one quarter of its orbit. The lit half is on the right side as seen from the Northern Hemisphere. Over the following days the illuminated area continues to grow beyond half, producing the Waxing Gibbous phase. "Gibbous" derives from the Latin word for "hump" and describes a shape that is more than half but not fully lit.
At the midpoint of the cycle, roughly 14.77 days after the New Moon, the Full Moon rises. Earth is now positioned between the Sun and the Moon, so the entire near side of the Moon is bathed in sunlight. Full Moons have captured human imagination throughout history and carry dozens of traditional names tied to seasons and agriculture, such as the Harvest Moon in September and the Wolf Moon in January.
After the Full Moon, the process reverses. The Waning Gibbous phase sees the illuminated area shrinking from the right side, with light remaining on the left. The Last Quarter (also called the Third Quarter) arrives when the Moon has completed three quarters of its orbit and shows exactly half illumination on the left side. The Waning Crescent follows, with only a thin sliver of light remaining on the left before the Moon returns to the New Moon phase and the cycle begins anew.
The Synodic Month
The time required for the Moon to complete one full cycle of phases is called the synodic month, and it averages 29.53058770576 days, which translates to 29 days, 12 hours, 44 minutes, and approximately 2.9 seconds. This period is distinct from the sidereal month (27.32 days), which measures how long it takes the Moon to return to the same position relative to the stars. The synodic month is longer because while the Moon orbits Earth, Earth itself is moving along its orbit around the Sun, so the Moon must travel a bit farther each cycle to realign with the Sun and Earth.
The mathematical relationship between these periods is expressed by the formula: 1/Psyn = 1/Psid − 1/Porb, where Psyn is the synodic period, Psid is the sidereal month, and Porb is Earth's orbital period around the Sun (approximately 365.25 days). This elegant equation explains why the lunar phase cycle is about two days longer than the Moon's actual orbital period around Earth.
The synodic month is not constant. It varies between approximately 29.27 and 29.83 days due to the eccentricity of both the Moon's orbit around Earth and Earth's orbit around the Sun. When the Moon is near perigee (its closest approach to Earth), it moves faster through its orbit, shortening the synodic month. Conversely, when the Moon is near apogee, the synodic month is slightly longer. The value 29.53059 days represents the mean synodic month averaged over many cycles.
Historical Context
The Moon's phases were among the first celestial phenomena that ancient humans learned to track systematically. Archaeological evidence suggests that Upper Paleolithic people carved notches into bones and antlers to count lunar cycles as far back as 30,000 years ago. The Lebombo bone from southern Africa, dated to approximately 35,000 BCE, bears 29 notch marks that many scholars interpret as a lunar tally.
Virtually every ancient civilization developed a calendar based at least partly on lunar phases. The Babylonians used a lunisolar calendar where months began with the first visible crescent after the New Moon. The ancient Egyptians originally used a lunar calendar before transitioning to a solar one for administrative purposes. The Chinese traditional calendar, the Hindu calendar, the Hebrew calendar, and the Islamic calendar all incorporate lunar months. The Islamic Hijri calendar is purely lunar, with twelve months of 29 or 30 days each, making its year approximately 354 days long and causing Islamic holidays to shift through the solar seasons over a roughly 33-year cycle.
The cultural significance of the Moon extends far beyond timekeeping. Many agricultural traditions tied planting and harvesting schedules to lunar phases, a practice that persists in some communities today. Fishermen have long observed the relationship between Moon phases and tidal patterns, since the gravitational pull of the Moon is the primary driver of ocean tides. The Full Moon in particular has inspired an enormous body of mythology, folklore, and art across every human culture, from the Aztec moon goddess Coyolxauhqui to the Japanese tradition of Tsukimi (moon viewing).
How We Calculate Moon Phase
Our moon phase calculator uses a well-established astronomical algorithm based on a known reference point and the mean synodic month. The algorithm starts from a precisely documented New Moon that occurred on January 6, 2000, at 18:14 UTC. This reference point, established through astronomical observation, serves as our epoch for lunar calculations.
The calculation proceeds as follows. First, we compute the number of days elapsed between the reference New Moon and the current date and time. This gives us the total time span in days. We then divide this elapsed time by the mean synodic month length (29.53058770576 days) and take the remainder using the modulo operation. The result is the moon age, which represents how many days have passed since the most recent New Moon.
From the moon age, we determine the phase name by mapping the age to one of eight named intervals. A moon age of 0 to approximately 1.85 days corresponds to the New Moon, 1.85 to 7.38 days is the Waxing Crescent, and so on through the full cycle. The illumination percentage is calculated using a cosine function: illumination = (1 − cos(age / synodic_month × 2π)) / 2. This produces a smooth curve from 0% at the New Moon through 100% at the Full Moon and back to 0%.
This method provides accuracy sufficient for general-purpose phase tracking. For professional astronomical applications requiring arc-second precision, more complex models such as Jean Meeus's algorithms or the Jet Propulsion Laboratory's ephemeris data would be used, as they account for perturbations from the Sun, Jupiter, and the non-uniform speed of the Moon in its elliptical orbit. For everyday purposes such as photography planning, gardening calendars, and tidal awareness, our algorithm is accurate to within a few hours.
Frequently Asked Questions
What is the current moon phase?
The current moon phase is Waning Gibbous with approximately 50% illumination. The moon is 22.1 days into the current lunation cycle. The phase updates continuously as the Moon progresses through its orbit around Earth.
How long is a lunar cycle?
A complete lunar cycle, known as a synodic month, lasts approximately 29.53 days (29 days, 12 hours, 44 minutes, and 2.9 seconds). This is the average time between successive New Moons. The actual duration varies slightly from cycle to cycle due to the elliptical shape of the Moon's orbit, ranging from about 29.27 to 29.83 days.
What are the 8 phases of the Moon?
The eight principal phases are New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent. "Waxing" means the illuminated area is growing, while "waning" means it is shrinking. "Crescent" indicates less than half is lit, while "gibbous" means more than half is illuminated.
When is the next full moon?
Based on the current moon age calculation, the next full moon is approximately 22.2 days away. Full Moons occur once per synodic month when the Moon is on the opposite side of Earth from the Sun, fully illuminating the near side of the lunar surface as seen from Earth.
Why does the Moon have phases?
The Moon has phases because we observe different portions of its sunlit surface as it orbits Earth. The Moon does not emit its own light; it reflects sunlight. Depending on the Moon's position relative to Earth and the Sun, we see varying amounts of the illuminated hemisphere. When the Moon is between Earth and the Sun (New Moon), the lit side faces away from us. When Earth is between the Moon and the Sun (Full Moon), we see the entire lit surface.
Does the Moon affect tides?
Yes. The Moon's gravitational pull is the primary cause of ocean tides on Earth. The Sun also contributes, but its tidal force is roughly 46% that of the Moon's. During Full Moon and New Moon phases, the Sun and Moon align and their gravitational effects combine to produce especially high tides (spring tides). During the quarter phases, their forces partially cancel, producing smaller tidal ranges (neap tides).