Moon Age Estimate
Estimate lunar phase, moon age, and illumination for a date using a mean synodic-month model.
How to use
- Choose a date.
- Calculate.
- Review phase name, lunar age in days, and illumination percentage.
Capabilities and scope
This lightweight estimate uses a known new-moon epoch and an average 29.53058867-day synodic cycle rather than a precision astronomical ephemeris.
How it works
Elapsed days from the reference new moon at 2000-01-06 18:14 UTC are reduced modulo 29.53058867 days. Illumination is approximated from cycle fraction f with `(1-cos(2πf))/2`.
Example
An age near 0 days is classified near new moon, while an age around half the cycle, about 14.8 days, is near full moon.
Useful for
- Get a rough idea of the Moon's appearance on a date
- Explore the lunar phase cycle for education
- Use a non-critical phase estimate in planning
Before you use it
- The model ignores orbital perturbations and observer location. Do not use it for precision astronomy, tides, or authoritative calendar/religious determinations.
Standards and references
Frequently asked questions
Will this exactly match an observatory ephemeris?
No. It is a mean-cycle approximation and can differ from precision astronomical calculations.
Does observer location change the result?
Location is not an input; the same selected date uses the same phase estimate.