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Moon Phase Calculator

This calculator calculates the Moon phase for an explicit civil time and IANA zone; the result is astronomical, not a claim about personality or events.

Calculate a reproducible Moon phase in calculator from explicit civil time, an IANA zone, declared boundaries, and engine settings.

Enter the calculation details

Enter a local civil date, time, and IANA zone to calculate the geocentric lunar phase.

Birth or civil-time details

Use the calendar date at the location of the event.

Enter the clock time shown at that location, not a converted UTC time.

Use UTC or a location ID such as America/New_York, Europe/Madrid, or Asia/Kolkata; abbreviations such as EST are not accepted.

Keep the safe default unless this clock time occurred twice during a daylight-saving change. Then choose the occurrence recorded at birth.

Fixed calculation settings

Algorithm
moon-phase-geocentric-v1
Interpretation
moon-phase-copy-1.0.0
Profile
geocentric-moon-phase-v1

Processed securely for this calculation and not savedOnly the fields required for the calculation are sent. They are not saved or added to the page URL.

Your entries are sent only to this same-origin calculation endpoint. The response is private, uses no-store caching, and is not added to the page URL.

Moon phase is an astronomical relationship between the Sun and Moon at a specified instant. It is different from Moon Sign, Rashi, and Nakshatra.

What the calculator reports

The calculator does not add a symbolic reading. Astronomical phase accuracy does not validate claims that the phase controls personality, relationships, health, or events.

Proposed phase boundaries

The method normalizes E = Moon longitude − Sun longitude into 0–360 degrees. It uses semi-open sectors: New [337.5°,360°) ∪ [0°,22.5°), Waxing Crescent [22.5°,67.5°), First Quarter [67.5°,112.5°), Waxing Gibbous [112.5°,157.5°), Full [157.5°,202.5°), Waning Gibbous [202.5°,247.5°), Last Quarter [247.5°,292.5°), and Waning Crescent [292.5°,337.5°).

Between the New and Full Moon turning points the direction is waxing; between Full and New it is waning. Values within the declared technical tolerance of either turning point are labelled turning-point. Values are not rounded before classification.

Date, time, and lunar age

The current geocentric form requires a local date, minute-precision local time, and IANA timezone, but no geographic location. It does not accept date-only or unknown-time input and never substitutes noon.

Method and limitations

Limitations

This v1 proposal is geocentric. It does not compute local moonrise, altitude, visibility, crescent sighting, eclipse circumstances, or a cultural calendar date. Those questions require other methods and sometimes geographic location and atmospheric assumptions.

Symbolic phase meanings are entertainment and reflection. They cannot diagnose, predict fertility, guide treatment, guarantee relationship outcomes, or replace scientific and professional information.

Privacy in the calculator

Minimum date/time inputs use a same-origin POST, are processed transiently, and return with private, no-store behavior. Date, time, timezone, phase, illumination, age, or hashes must not enter URLs, storage, logs, traces, replay, analytics, metadata, advertising, or quiz parameters.

Explanatory example

A synthetic fixture might provide an elongation of exactly 67.5 degrees. Under the declared semi-open sectors, that belongs to First Quarter, not Waxing Crescent. The test verifies unrounded classification and the engine version. This is a boundary illustration, not a personal result.

Frequently asked questions

Can I calculate a Moon phase now?

Is Moon phase the same as Moon Sign?

No. Phase is the Sun-Moon angle; Moon Sign or Rashi classifies the Moon's zodiac longitude.

Do I need a city?

Not for the proposed geocentric phase. You need a timezone to interpret local date and time.

Can I submit only a date?

How is lunar age calculated?

The runtime searches for the previous New Moon and measures elapsed days from it. That event calculation still needs broader independent verification.

Conclusion

Sources

  • NASA JPL, Horizons System Manual, intended for independent reference research rather than runtime dependency.

Related tools

  • Sun Sign Calculator
  • Rashi Calculator
  • Nakshatra Calculator