A moon phase describes the appearance of the illuminated portion of the Moon as seen from Earth. As the Moon orbits our planet, the angle between the Sun, Earth, and Moon changes, causing different portions of the Moon's surface to be lit. The complete cycle takes approximately 29.53 days — known as a synodic month or lunation.

This tool uses a well-established astronomical algorithm based on the synodic month cycle (29.530588853 days) referenced to the precisely observed New Moon of January 6, 2000 (18:14 UTC). For any date between 1900 and 2100, the predicted moon phases are accurate to within ±2 hours for major phases. The illumination percentage is calculated using a continuous trigonometric model.

The 8 principal phases are: New Moon (0% illuminated, Moon between Earth and Sun), Waxing Crescent (1-49%, growing), First Quarter (50%, right half lit in Northern Hemisphere), Waxing Gibbous (51-99%, nearly full), Full Moon (100%, Earth between Moon and Sun), Waning Gibbous (99-51%, shrinking), Last Quarter (50%, left half lit), and Waning Crescent (49-1%, fading to New Moon).

A Blue Moon refers to the second Full Moon occurring within a single calendar month. Since the lunar cycle is about 29.5 days and most months are 30 or 31 days long, occasionally a month will have two Full Moons — the second is called a Blue Moon. This happens approximately every 2.5 to 3 years. There is also a seasonal definition: the third Full Moon in an astronomical season that has four Full Moons.

Scientific studies have shown mixed results. Some research suggests that people may experience slightly reduced sleep quality (about 20-30 minutes less deep sleep) around the Full Moon, while other studies find no significant correlation. The belief that moon phases influence mood, crime rates, or hospital admissions is widespread in folklore but lacks strong empirical evidence. The lunar effect remains a topic of ongoing research and cultural fascination.

A Supermoon occurs when a Full Moon (or New Moon) coincides with the Moon's perigee — its closest approach to Earth in its elliptical orbit. A Supermoon can appear up to 14% larger and 30% brighter than a Full Moon at apogee (farthest point). The term was coined by astrologer Richard Nolle in 1979. Supermoons happen about 3-4 times per year.

Many gardeners follow lunar planting calendars. The general guideline: plant above-ground crops (leafy greens, fruits) during the Waxing Moon (New to Full), when sap flow is believed to increase. Plant root crops (carrots, potatoes, bulbs) during the Waning Moon (Full to New). The New Moon and Full Moon days are often considered rest periods. Use this tool to identify these optimal windows for your gardening activities.

The lunar synodic month (29.53 days) does not align evenly with our Gregorian calendar months (28-31 days) or the solar year (365.24 days). This misalignment causes moon phases to shift by about 10-11 days each year. Over a 19-year Metonic cycle, the phases return to approximately the same calendar dates. This is why a Full Moon on Christmas, for example, is relatively rare — occurring about once every 19 years.

A synodic month (29.53 days) is the time it takes for the Moon to complete one full cycle of phases (New Moon to New Moon), measured relative to the Sun. A sidereal month (27.32 days) is the time for the Moon to complete one orbit around Earth relative to the fixed stars. The difference exists because Earth is also moving around the Sun, so the Moon must travel slightly farther to realign with the Sun for the next New Moon.

This tool focuses on moon phase prediction and illumination data. Moonrise and moonset times vary significantly based on your geographic location (latitude and longitude) and the Moon's declination. On average, the Moon rises about 50 minutes later each day. For precise local moonrise/moonset times, we recommend using a dedicated astronomical almanac or app that incorporates your specific coordinates.