Time & Sun
World Moon Phase & Lunar Calendar
Find the moon phase, age and illumination for any date — for photography, gardening, tides and simply knowing the night sky.
Full Moon
Age
15.5 days
Illumination
99%
Cycle
29.53 d
Understanding the lunar cycle
The Moon orbits Earth roughly every 27.3 days, but a full phase cycle — new moon to new moon — takes 29.53 days. The difference arises because Earth itself moves around the Sun, so the Moon must travel slightly more than one full orbit to return to the same position relative to the Sun. This 29.53-day cycle, the synodic month, is the basis of every lunar calendar.
As the Moon orbits, the angle between the Sun, Earth and Moon changes, and so does the portion of the Moon's Earth-facing side that is illuminated. We perceive this as the eight phases, from new (invisible) through crescent, quarter and gibbous to full, then back through the waning versions.
The eight phases explained
The cycle has four primary phases and four intermediate ones. New Moon occurs when the Moon is between Earth and Sun, its near side in shadow. First Quarter (half-illuminated, waxing) comes about a week later. Full Moon, when the Moon is opposite the Sun and fully lit, comes around day 14. Last Quarter (half-illuminated, waning) follows at about day 22.
Between these are the crescents (sliver of light, growing or shrinking) and the gibbous phases (more than half lit, growing toward or shrinking from full). 'Waxing' means the illuminated portion is increasing; 'waning' means it is decreasing. The emoji in this tool reflects the current phase at a glance.
Moon age and illumination
Moon age is simply the number of days since the last new moon, running from 0 to 29.53. It is the most intuitive single number for where the Moon is in its cycle. Illumination is the percentage of the Moon's disk that is lit, varying from 0% at new moon to 100% at full, following a smooth cosine curve rather than changing linearly.
The two are related but not identical: a 7-day-old moon is at first quarter with 50% illumination; a 14.7-day-old moon is full with 100% illumination. This tool reports both so you can describe the Moon precisely for any purpose.
Lunar calendars and culture
Many of the world's calendars are lunar or lunisolar: the Islamic calendar is purely lunar (12 months of 29.53 days ≈ 354 days, so it drifts against the solar year). The Chinese, Hebrew and Hindu calendars are lunisolar, adding leap months to stay aligned with the seasons. Easter's date is computed from lunar tables, which is why it moves each year.
Cultural and religious observances — Ramadan, Lunar New Year, Diwali, Passover — are tied to lunar phases. Knowing the moon phase for a future date helps plan around these observances, whether for travel, business or personal practice.
Photography and the night sky
Moon phase transforms night photography. A full moon lights the landscape brightly enough for long exposures that look almost like daylight, and it drowns out faint stars. A new moon gives the darkest skies — ideal for Milky Way and deep-sky photography, but useless for moonlit landscapes. The quarters offer a balance and a half-illuminated Moon that photographs well in its own right.
Moonrise and moonset times depend on phase and location just as sunrise and sunset do. A full moon rises around sunset and sets around sunrise; a new moon is near the Sun and invisible at night. Planning tools that pair moon phase with moonrise time are invaluable for night shoots.
Tides, gardening and folklore
Tides are driven by the Moon, with the highest (spring) tides near new and full moon and the lowest (neap) tides near the quarters. Coastal activities from fishing to photography are planned around the tide, which means around the moon phase. The same gravity also slightly affects some animal behaviour.
Lunar gardening traditions sow and harvest by moon phase, and while the scientific evidence is thin, the rhythm is harmless and keeps gardeners observing their plants. Whether for science or tradition, knowing the moon phase connects you to a cycle humans have tracked for millennia.
Frequently Asked Questions
What is a moon phase?
A moon phase is the portion of the Moon's near side that is illuminated by the Sun as seen from Earth. It cycles through eight named stages as the Moon orbits Earth, completing a full cycle (one synodic month) every 29.53 days.
How is the moon age calculated?
Moon age is the number of days since the most recent new moon. This tool uses a well-known approximation (Conway's algorithm) accurate to within about a day for general reference; precise ephemeris calculations track the Moon to the second.
What is illumination?
Illumination is the percentage of the Moon's visible disk that is lit by the Sun. It is 0% at new moon, 50% at the quarters and 100% at full moon, following a cosine curve across the cycle.
Why is the cycle 29.53 days?
The synodic month (new moon to new moon) is 29.53 days because the Moon must catch up with Earth's motion around the Sun to return to the same phase. The Moon's orbital period relative to the stars is shorter (27.32 days, the sidereal month).
How accurate is this calculator?
It is accurate to about a day, which is sufficient for planning, photography and general reference. For exact astronomical work, use a full ephemeris; the phase shown here may differ by up to a day near the quarter or full transitions.
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