eye-spy/services/sky.mjs

// Sky service: target info, "what should I look at" recommendations, and overlay objects.
// Positions come from CelestialService.predict() (astronomy-engine, fully offline for Sun/Moon/planets/stars).
import * as Astronomy from 'astronomy-engine';
import { STARS } from '../lib/stars.mjs';
import { angularSeparation } from '../lib/geo.mjs';

// Bundled deep-sky showpieces (J2000 RA hours, Dec deg, visual magnitude). Swap for OpenNGC later.
const DSO = [
  ['m31', 'M31 Andromeda Galaxy', 'Galaxy', 0.712, 41.27, 3.4],
  ['m42', 'M42 Orion Nebula', 'Nebula', 5.588, -5.39, 4.0],
  ['m45', 'M45 Pleiades', 'Open Cluster', 3.79, 24.12, 1.6],
  ['m44', 'M44 Beehive', 'Open Cluster', 8.667, 19.67, 3.7],
  ['m13', 'M13 Hercules Cluster', 'Globular', 16.695, 36.46, 5.8],
  ['m8', 'M8 Lagoon Nebula', 'Nebula', 18.063, -24.38, 6.0],
  ['m27', 'M27 Dumbbell Nebula', 'Planetary Nebula', 19.994, 22.72, 7.4],
  ['m57', 'M57 Ring Nebula', 'Planetary Nebula', 18.893, 33.03, 8.8],
  ['m81', 'M81 Bode\'s Galaxy', 'Galaxy', 9.926, 69.07, 6.9],
  ['m51', 'M51 Whirlpool Galaxy', 'Galaxy', 13.498, 47.2, 8.4],
].map(([id, label, type, ra, dec, mag]) => ({ id, label, type, ra, dec, mag, spec: `radec:${ra},${dec}` }));

const PLANETS = ['mercury', 'venus', 'mars', 'jupiter', 'saturn', 'uranus', 'neptune'];
const OUTER = ['Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune'];
const r = (v, d = 1) => (v == null ? v : Math.round(v * 10 ** d) / 10 ** d);
const iso = (t) => t?.date?.toISOString?.() ?? null;
const cap = (s) => s[0].toUpperCase() + s.slice(1);

export class SkyService {
  #c;
  #t;

  constructor({ celestial, telemetry }) {
    this.#c = celestial;
    this.#t = telemetry;
  }

  #candidates() {
    return [
      { id: 'body:moon', label: 'Moon', type: 'Moon', spec: 'moon' },
      ...PLANETS.map((p) => ({ id: `body:${p}`, label: cap(p), type: 'Planet', spec: `body:${p}` })),
      ...Object.entries(STARS).map(([k, s]) => ({ id: `star:${k}`, label: s.label, type: 'Star', mag: s.mag ?? 2, spec: `star:${k}` })),
      ...DSO.map((d) => ({ ...d, id: `dso:${d.id}` })),
    ];
  }

  /** Detail for one target: position + (for solar-system bodies) phase, magnitude, elongation, opposition, rise/transit/set. */
  info(spec) {
    const date = this.#t.now();
    const p = this.#c.predict(spec, { date });
    const out = { ...p };
    if (p.target.kind !== 'body') return out;

    const name = p.target.label;
    const o = new Astronomy.Observer(p.observer.lat, p.observer.lon, p.observer.altM);
    const ill = Astronomy.Illumination(name, date);
    out.magnitude = r(ill.mag);
    out.phasePct = r(ill.phase_fraction * 100, 0);
    out.distanceKm = Math.round(p.distanceAu * 149_597_870.7);
    out.elongationDeg = name === 'Sun' ? 0 : r(Astronomy.AngleFromSun(name, date));
    out.events = {
      rise: iso(Astronomy.SearchRiseSet(name, o, +1, date, 2)),
      transit: iso(Astronomy.SearchHourAngle(name, o, 0, date).time),
      set: iso(Astronomy.SearchRiseSet(name, o, -1, date, 2)),
    };
    if (OUTER.includes(name)) {
      out.oppositionPct = r((out.elongationDeg / 180) * 100, 0); // 100% = exactly at opposition
      out.nextOpposition = iso(Astronomy.SearchRelativeLongitude(name, 180, date));
    }
    return out;
  }

  /** Ranked list of what's worth observing right now. */
  recommend({ limit = 8, minAlt = 15 } = {}) {
    const date = this.#t.now();
    const moon = this.#c.predict('moon', { date });
    const moonIllum = (1 - Math.cos((Astronomy.MoonPhase(date) * Math.PI) / 180)) / 2;
    const rows = [];

    for (const c of this.#candidates()) {
      let p;
      try {
        p = this.#c.predict(c.spec, { date });
      } catch {
        continue;
      }
      if (p.alt < minAlt) continue;

      const row = { id: c.id, spec: c.spec, label: c.label, type: c.type, az: p.az, alt: p.alt, why: [] };
      let mag = c.mag;
      let score = (Math.min(p.alt, 70) / 70) * 40;

      if (c.type === 'Planet' || c.type === 'Moon') {
        const ill = Astronomy.Illumination(c.label, date);
        mag = ill.mag;
        row.phasePct = r(ill.phase_fraction * 100, 0);
        const el = Astronomy.AngleFromSun(c.label, date);
        if (OUTER.includes(c.label)) {
          row.oppositionPct = r((el / 180) * 100, 0);
          if (el > 150) { score += 15; row.why.push('near opposition'); }
        }
        if (el < 20 && c.type === 'Planet') { score -= 30; row.why.push('close to the Sun'); }
        if (c.type === 'Planet') score += 10;
      }
      const moonSep = angularSeparation(p.az, p.alt, moon.az, moon.alt);
      if (c.type !== 'Moon' && mag > 4 && moonSep < 40) {
        score -= (40 - moonSep) * 0.6 * moonIllum;
        row.why.push('washed out by Moon');
      }
      score += Math.max(0, 10 - (mag ?? 10)) * 3;
      if (p.alt > 50) row.why.push('high in sky');

      row.mag = r(mag);
      row.moonSepDeg = r(moonSep, 0);
      row.score = r(score, 0);
      rows.push(row);
    }
    return rows.sort((a, b) => b.score - a.score).slice(0, limit);
  }

  /** Everything above (roughly) the horizon, for the sky-map / live overlay. */
  objects() {
    const date = this.#t.now();
    const out = [];
    for (const c of this.#candidates()) {
      try {
        const p = this.#c.predict(c.spec, { date });
        if (p.alt > -5) out.push({ id: c.id, spec: c.spec, label: c.label, type: c.type, mag: c.mag ?? null, az: p.az, alt: p.alt });
      } catch { /* skip */ }
    }
    return { time: date.toISOString(), objects: out };
  }
}