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Lizely

Birthday Moon Phase Calculator

Calculate the geocentric Moon phase for a birth date, local time, and documented UTC or UTC-equivalent offset, with illumination, nearby primary events, and a clearly warned unknown-time approximation.

Privacy: your files never leave your device. All processing happens locally in your browser.

How to use

  1. 1.Enter the local birth date, clock time, and documented UTC or UTC-equivalent offset for that moment, then calculate the instant estimate.
  2. 2.If the time is unknown, deliberately choose the approximation mode and read its Phase-boundary approximation and possible-label warnings.
  3. 3.Review the normalized UTC instant, angle, illumination, eight-stage Lizely display band, and nearby primary events together.

About Birthday Moon Phase Calculator

Birthday Moon Phase Calculator resolves a supplied local birth date, clock time, and documented UTC or UTC-equivalent offset to one auditable proleptic UTC-like instant. It then calculates the geocentric Moon-Sun ecliptic-longitude difference, illuminated fraction, a convenient eight-stage display label, and the primary phase events around that instant. The result shows both the entered local time and normalized calculation time. It does not request a birthplace or location permission because geocentric phase is an Earth-center quantity rather than a local horizon, moonrise, weather, or visibility calculation.

Exact mode requires a date, time, and documented UTC or UTC-equivalent offset for that place and moment. Before standard time zones, local mean time may not map to a reliable modern offset, so early-date results are proleptic UTC-like estimates. The offset is entered explicitly because the browser's current time zone cannot reliably reconstruct historical daylight-saving or political time-zone rules. Conversion uses deterministic civil-time arithmetic instead of parsing a free-form date string. Invalid dates, clocks, offsets, and normalized calculation instants outside 1700 through 2100 are rejected before the astronomy calculation runs.

An optional unknown-time mode is deliberately less certain. It calculates local noon and labels the result Phase-boundary approximation beside the output. It also compares the start and end of that local day. If the broad display label differs, both possibilities are shown instead of presenting noon as definitive. The tool checks whether a New Moon, First Quarter, Full Moon, or Last Quarter instant occurred during the local day and explains that an unknown birth time may fall before or after the event.

The four primary phases are instantaneous angular events: 0 degrees for New Moon, 90 for First Quarter, 180 for Full Moon, and 270 for Last Quarter. The broad eight-stage names are separate. Lizely places boundaries halfway between primary angles: New Moon wraps across 337.5 to 22.5 degrees, then Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent each occupy a disclosed 45-degree band. These equal-width bands are a Lizely display convention, not an official USNO or NASA classification.

Accuracy is tested rather than implied. Twelve literal minute-resolution events from the official United States Naval Observatory service cover all four primary phases, a leap year, year rollovers, and the 1700 and 2100 limits. The pinned Astronomy Engine implementation must find every event within two minutes of the USNO fixture. NASA is used to cross-check familiar phase terminology and physical explanation. Neither official service is called when a visitor uses the page.

The calculation runs locally through the already pinned astronomy-engine 2.1.19 package behind a narrow Lizely adapter. No birth input is uploaded, stored, or sent to USNO, NASA, a CDN, or a paid service. Once the page assets are loaded, the result works without a network connection.

Astronomical estimate only. The result does not claim second-level or professional-observatory precision and is not suitable for navigation, safety, tides, religious observance, local visibility, or other time-critical decisions. The tool does not infer personality, compatibility, luck, fate, or life advice from a birth phase.

Time-history caveat: the numeric input is a documented UTC offset or UTC-equivalent offset, not a promise that modern UTC or a standard civil time zone existed on the entered date. Before standard time zones, local mean time may not map to a reliable modern offset. Early-date output is therefore a proleptic UTC-like estimate, and the entered convention remains visible in the result.

Methodology & sources

Resolve valid local civil fields and a signed documented UTC or UTC-equivalent offset to one proleptic UTC-like instant. Before standard time zones, local mean time may not map to a reliable modern offset. Use the narrow local Astronomy Engine 2.1.19 adapter for geocentric phase angle, illumination, and surrounding 0, 90, 180, and 270 degree events. Map the angle to disclosed Lizely half-way display bands. Unknown-time mode uses local noon, compares local-day endpoints, and searches primary events within the offset-defined local day. Validate twelve literal USNO events within two minutes. Make no runtime network or location request.

Frequently asked questions

Why does the calculator ask for a UTC offset?
A local clock time is not a unique instant without the offset that applied then. The browser's current offset may not match historical daylight-saving or political time-zone rules, so the tool makes the conversion explicit.
What happens if I do not know the birth time?
The optional approximation uses local noon, checks the start and end of the day, and warns about label or primary-event boundaries. It is visibly marked Phase-boundary approximation and is never presented as exact.
Are the eight stage boundaries official USNO categories?
No. USNO supplies the four primary event meanings and fixture times. Lizely's eight equal-width angle bands are a disclosed product display convention.

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