moon_sighting

Lunar crescent visibility for Dart and Flutter. Moon phase, topocentric position, illumination, and Yallop/Odeh crescent criteria using Meeus algorithms. Zero dependencies.

Uses Meeus lite algorithms (~0.3 degree accuracy). The companion TypeScript package (moon-sighting on npm) uses JPL DE442S ephemeris for sub-arcminute precision.

Installation

dependencies:
  moon_sighting: ^1.0.0

Quick Start

import 'package:moon_sighting/moon_sighting.dart';

// Current moon phase
final phase = getMoonPhase();
print('${phase.phaseName} ${phase.phaseSymbol}');
print('Illumination: ${phase.illumination.toStringAsFixed(1)}%');

// Moon position for an observer
final pos = getMoonPosition(DateTime.now(), 51.5074, -0.1278, elevation: 10);
print('Azimuth:  ${pos.azimuth.toStringAsFixed(1)}');
print('Altitude: ${pos.altitude.toStringAsFixed(1)}');

// Crescent visibility estimate (pass a post-sunset time)
final vis = getMoonVisibilityEstimate(
  DateTime.utc(2025, 3, 31, 18, 30),
  21.4225, 39.8262, // Makkah
);
print('Zone: ${vis.zone.label}');            // A through D
print('Visible naked eye: ${vis.isVisibleNakedEye}');

API

Five public functions. See the API Reference for full field tables.

Function	Returns	Description
`getMoonPhase([DateTime?])`	`MoonPhaseResult`	Phase name, illumination, age, next events
`getMoonPosition(DateTime?, lat, lon)`	`MoonPosition`	Topocentric az/alt, distance
`getMoonIllumination([DateTime?])`	`MoonIlluminationResult`	Fraction, phase cycle, bright limb angle
`getMoonVisibilityEstimate(DateTime?, lat, lon)`	`MoonVisibilityEstimate`	Odeh V parameter, visibility zone A-D
`getMoon(DateTime?, lat, lon)`	`MoonSnapshot`	All four results combined

Accuracy

All positions use Meeus (1998) approximations: Moon longitude < 0.3 deg, latitude < 0.2 deg, distance ~300 km. New/full moon times are within ~2 hours.

moon-sighting (TypeScript) - Full accuracy with DE442S ephemeris
nrel-spa (TypeScript) - NREL Solar Position Algorithm
pray-calc (TypeScript) - Islamic prayer times

Acknowledgments

Crescent visibility criteria from:

B.D. Yallop, "A Method for Predicting the First Sighting of the New Crescent Moon," NAO Technical Note No. 69, 1997.
M.Sh. Odeh, "New Criterion for Lunar Crescent Visibility," Experimental Astronomy 18(1), 39-64, 2006.
Jean Meeus, "Astronomical Algorithms," 2nd ed., Chapters 47 and 48.

License

MIT

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