astronomia 0.1.0

Astronomical algorithms in Dart — positions of Sun, Moon, and planets, eclipses, phases, coordinates, magnitudes, and more. Based on Jean Meeus's "Astronomical Algorithms".

Astronomia

Astronomical algorithms in Dart, ported from Jean Meeus's Astronomical Algorithms (2nd Ed.) via the Go meeus library and the JS astronomia library.

Features

45 modules covering positional astronomy, celestial mechanics, and calendar computations:

Category	Modules
Time & Calendar	Julian Day, Delta T, sidereal time, Easter (Gregorian & Julian)
Coordinates	Ecliptic/equatorial/horizontal/galactic transforms, precession, nutation, parallax, refraction, aberration
Sun	Solar position, solstices & equinoxes, sunrise/sunset, equation of time
Moon	Lunar position, phases (new/first/full/last), illumination, nodes, apsis (perigee/apogee), max declination
Planets	Kepler's equation (6 solvers), orbital elements, conjunctions, oppositions, elongations, Pluto heliocentric coords
Orbits	Elliptic, parabolic, and near-parabolic motion, velocity, orbit length
Planet Details	Illumination & magnitudes, Jupiter physical ephemeris, Galilean moon positions
Geodesy	Earth ellipsoid, geodetic distance, parallax constants
Stellar	Magnitude arithmetic, binary star orbits, angular separation
Misc	Eclipse prediction, semidiameters, sundials, smallest circle, collinearity

Getting started

dependencies:
  astronomia: ^0.1.0

import 'package:astronomia/astronomia.dart';

Usage

The barrel import gives you foundations (julian, coordinates, nutation, etc.):

import 'package:astronomia/astronomia.dart';

void main() {
  // Julian Day for J2000.0
  final jd = calendarGregorianToJD(2000, 1, 1.5);
  print('J2000.0 = JD $jd'); // 2451545.0

  // Date of Easter 2025
  final e = gregorian(2025);
  print('Easter 2025: April ${e.day}'); // April 20
}

For specialized modules, import them directly — many share common names like position, radius, eccentricity, so prefixed imports keep things clear:

import 'package:astronomia/astronomia.dart';
import 'package:astronomia/src/solar/solar.dart' as solar;
import 'package:astronomia/src/moonposition/moonposition.dart' as moon;
import 'package:astronomia/src/moonphase/moonphase.dart' as phase;
import 'package:astronomia/src/globe/globe.dart' as globe;
import 'package:astronomia/src/angle/angle.dart' as angle;

void main() {
  final jd = calendarGregorianToJD(2000, 1, 1.5);

  // Solar ecliptic longitude
  final sunLon = solar.apparentLongitude(jd);

  // Moon position
  final pos = moon.position(jd);
  print('Moon: lon=${toDeg(pos.lon)}°, lat=${toDeg(pos.lat)}°');

  // Next new moon
  final newMoonJDE = phase.newMoon(2025.5);

  // Earth surface distance (km)
  final km = globe.distance(lat1, lon1, lat2, lon2);

  // Angular separation between two stars
  final d = angle.sep(ra1, dec1, ra2, dec2);
}

Conventions

• All angles are in radians (double). Use toRad() / toDeg() to convert.
• Time is represented as Julian Day numbers (double).
• Multi-value returns use Dart records: ({double lon, double lat, double delta}).
• The J2000.0 epoch constant is j2000 = 2451545.0.

Status

This is a 0.1.0 release. 45 of 57 modules are fully ported. The remaining 12 are stubs awaiting VSOP87 planetary theory data (needed for high-precision planetary positions, Saturn rings, and a few dependent calculations).

All ported modules are tested against examples from Meeus's book.

References

• Meeus, Jean. Astronomical Algorithms. 2nd ed. Richmond: Willmann-Bell, 1998.
• soniakeys/meeus (Go)
• commenthol/astronomia (JS)

License

MIT