🌙 Moon Phase Calculator
Find the moon phase for any date with illumination percentage.
What is this tool?
The Moon Phase Calculator is a free online tool that shows the phase of the moon for any date, past or future. Whether you are planning a photography session, a gardening schedule, a stargazing trip, or just curious about the lunar cycle, this calculator gives you accurate moon phase information instantly. The moon goes through a complete cycle of phases every 29.53 days, known as the synodic month. Starting from the new moon (when the moon is invisible from Earth), the phases progress through waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, and waning crescent, before returning to new moon. Each phase has a specific illumination percentage, from 0% at new moon to 100% at full moon. This calculator uses astronomical algorithms to determine the precise moon phase for any date from 1900 to 2100. It shows the current phase name, the illumination percentage, the moon's age in days since the last new moon, and the date of the next full moon and next new moon. All calculations happen locally in your browser using well-established astronomical formulas.How it works
The calculator uses astronomical algorithms based on the work of Jean Meeus, a renowned astronomical calculator. The core formula computes the moon's position relative to the Earth and Sun to determine the illuminated fraction. The synodic month (the time from one new moon to the next) averages 29.53059 days. The calculator tracks the number of days since a known new moon reference point and uses modular arithmetic to find the current position in the lunar cycle. The moon's age is this day count modulo 29.53. The illumination percentage is calculated using the phase angle, which is the angle between the Earth, Moon, and Sun. At new moon (phase angle 0°), the illuminated fraction is 0%. At full moon (phase angle 180°), it is 100%. The formula for illumination is: (1 - cos(phase_angle)) / 2, expressed as a percentage. The phase name is determined from the moon's age: 0-1.85 days (new), 1.85-5.54 (waxing crescent), 5.54-9.23 (first quarter), etc. The next full moon and new moon dates are computed by projecting forward in the lunar cycle.How to use
- Select or type the date you want to check.
- The moon phase for that date appears instantly.
- View the illumination percentage and moon age.
- See the dates of the next full moon and new moon.
- Use the date picker to explore different dates.
Frequently Asked Questions
Frequently Asked Questions
How accurate is the moon phase calculation?
The calculation uses well-established astronomical algorithms accurate to within a fraction of a day. For any date between 1900 and 2100, the moon phase is calculated precisely using the synodic month average of 29.53 days.
Why do moon phases matter for gardening?
Traditional gardening by the moon suggests planting above-ground crops during the waxing moon (new to full) and root crops during the waning moon (full to new). While scientific evidence is mixed, many gardeners follow this practice.
What is a supermoon?
A supermoon occurs when the full moon coincides with the moon's closest approach to Earth (perigee). The moon appears about 14% larger and 30% brighter than at its furthest point. This calculator shows the phase but does not specifically flag supermoons.
Can I check moon phases for historical dates?
Yes. The calculator works for any date from 1900 to 2100. You can check what the moon looked like on your birthday, a historical event, or any past date.
Tips & Advice
The lunar cycle has influenced human culture for millennia, from calendar systems to agricultural practices to mythology. For photography, the days around the full moon offer the best natural lighting for night scenes, while new moon nights are ideal for astrophotography and stargazing. The blue moon (the second full moon in a calendar month) occurs roughly every 2.7 years. Lunar eclipses can only occur during a full moon, when the Earth passes between the Sun and Moon. Solar eclipses occur only during a new moon. The moon rises about 50 minutes later each day, which is why it appears in different parts of the sky at the same time on different days.