The Hesapstan moon phase calculator is designed to calculate which phase the Moon is in (new moon, crescent, full moon, etc.) on a date you enter, along with the estimated illumination percentage for that phase.
How is the moon phase calculated?
The Moon completes one full cycle around Earth (a synodic month) in approximately 29.53 days, and its illuminated portion as seen from Earth changes throughout this cycle as its position relative to the Sun changes. This tool calculates the number of days elapsed since a known reference new moon date (January 6, 2000) and positions it within the 29.53-day cycle to find the phase and approximate cycle position for the date you enter.
The eight primary phases, in order, are: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, Waning Crescent.
How accurate is the result?
This calculation is an approximation based on the Moon's average cycle length; the true synodic month length varies slightly due to the elliptical orbits of the Moon and Earth. As a result, the exact moment of a phase change can differ by up to a day from the actual observed moment.
What does this tool not calculate?
- It does not calculate moonrise/moonset times for a specific location; it only provides the phase and approximate illumination percentage.
- It does not calculate special celestial events such as lunar or solar eclipses.
- It is not a second-precision astronomical ephemeris; it is accurate enough for everyday planning and general curiosity, not for scientific observation.
Frequently Asked Questions
How is the moon phase calculated?
The number of days elapsed since a known reference new moon date is positioned within the Moon's average 29.53-day cycle length.
What are the eight moon phases?
New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent.
Is this calculation exactly accurate?
No, this is an approximate estimate. Since the Moon's actual cycle length varies slightly, the exact moment of a phase change can differ by up to a day.
Does this tool calculate moonrise or moonset times?
No. This tool only calculates the Moon's phase and estimated illumination; it does not calculate moonrise/moonset times.