Frequently Asked Questions
What is the synodic month this uses?
It uses the average new-moon-to-new-moon cycle of about 29.53 days. The moon age is measured from a known new moon and reduced into that cycle.
How accurate is the phase?
The phase name is reliable to within about a day. Because the model uses an average cycle, exact times can differ from a precise almanac by several hours.
Can a 50 percent lit moon be two different phases?
Yes. A half-lit moon is a first quarter when waxing and a last quarter when waning, so illumination alone does not name the phase; the trend matters.
What time of day does the result represent?
The calculation is anchored to midday Universal Time on the date you choose, so local phase timing may shift slightly with your time zone.
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Aviation & Marine Disclaimer: Educational only. Not for flight or navigation operations.
This calculator is for educational and informational purposes only and is not a substitute for official flight or navigation planning. Always use current performance charts, an approved POH/AFM, certified navigation tools, and follow all applicable FAA, ICAO, USCG, and other regulatory guidance. Verify all results independently before operating any aircraft or vessel.