Lunar phase
Mean-lunation estimateMoon Phase Calculator
Estimate moon phase, age and illumination for a selected date and time zone.
Approximate lunar phase
Waning Crescent21.5% illuminated · age 25.0 daysThis estimate uses a mean 29.530588853-day synodic month anchored to a known new-moon epoch. It is useful for general planning, not precision ephemeris work.
Precision boundary
Hourberry uses a mean synodic month for planning-level phase estimates. Reference certification checks expected phase/day agreement; the result is not intended as precision ephemeris data.