Moon Phase Approximation Calculator
Meanconstant29.530588853daysynodiccyclefromdeclaredJD2451550.1approxnewmoonanchor,NOT elongation-derivedage/trueeclipse/ephemeriscalculation. Actual independent model/unit/frame/epoch/calibration and applicable measurement established;not precise ephemeris,forecast,geodesy operation,identity or safety approval.
Description
A mean synodic lunar cycle is a simple repeating phase clock.
A mean synodic lunar cycle is a simple repeating phase clock.1
This tool reports mean lunar age and cycle fraction from a Julian day in UTC; it does not calculate a modern ephemeris, illumination fraction or visibility.
When to use Moon Phase Approximation Calculator
Use this tool to apply the stated moon phase approximation calculator operation with an explicit input and unit basis.
How to use Moon Phase Approximation Calculator and how it works
- Establish the measurement basis and units described above.
- Enter actualJulianDayUtc and run the tool.
- Read result.meanSynodicAgeDays, result.meanCycleFraction using the output meanings below.
- If input is rejected, correct the stated type, range, ordering or alignment issue and rerun; review successful results under the declared convention.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| actualJulianDayUtc | Julian Day Utc. Units, ordering and applicable branch are specified in the algorithm. | number | required; finite; further conditions in the algorithm |
Subtract epoch 2451550.1 and normalize modulo 29.530588853 days into a nonnegative cycle. Return the wrapped age and age divided by the period; dates before the epoch use the same wrapping rule.
ageDays = positiveModulo(JDutc−2451550.1, 29.530588853); fraction = ageDays/29.530588853 Apply the declared units, ordering and branch conditions.
| Output field | Meaning | Value type |
|---|---|---|
| result | Object containing the declared output fields. | object |
| result.meanSynodicAgeDays | Wrapped age from zero up to, but excluding, the declared mean lunar period. | number |
| result.meanCycleFraction | Mean-cycle age divided by the period, in [0,1). This is not illuminated fraction. | number |
{
"input": {
"actualJulianDayUtc": 2451550.1
},
"output": {
"result": {
"meanSynodicAgeDays": 0,
"meanCycleFraction": 0
}
}
}Limitations and assumptions
The output applies the declared operation to the values you supply. Establish the measurement basis, units, coefficients and any caller-selected rules before interpreting it. The tool does not independently collect or verify observations or decide whether a model or reference applies.
Supply explicit required fields with the documented types and dense aligned arrays. Unknown fields, wrong types and nonfinite numbers are rejected. Branch-specific constraints are explained above. A returned boolean, signed difference or tied result follows the stated convention; an input error instead means the required input contract was not satisfied. Very large inputs or outputs may be rejected by shared resource limits.
Alternative or Complementary methods
For a related operation, use Moon Apparent Size Perigee/Apogee Arcmin. A spherical Moon’s apparent limb diameter grows when its center is closer to the observer.
For a related operation, use Golden Hour Duration By Latitude Lookup. Golden-hour definitions vary by photographic convention.
References
-
Moon Phase Approximation Calculator — tool.io
Similar or alternative tools
- Moon Apparent Size Perigee/Apogee Arcmin
A spherical Moon’s apparent limb diameter grows when its center is closer to the observer.
- Golden Hour Duration By Latitude Lookup
Golden-hour definitions vary by photographic convention.