init

lib/errors.mjs

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+/** Error intended to be returned by the HTTP API. */
+export class ServiceError extends Error {
+  constructor(code, message, status = 500, details = undefined) {
+    super(message);
+    this.name = 'ServiceError';
+    this.code = code;
+    this.status = status;
+    if (details !== undefined) this.details = details;
+  }
+}

lib/geo.mjs

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+export const rad = (degrees) => (degrees * Math.PI) / 180;
+export const deg = (radians) => (radians * 180) / Math.PI;
+export const wrap360 = (degrees) => ((degrees % 360) + 360) % 360;
+export const wrap180 = (degrees) => ((degrees + 180) % 360 + 360) % 360 - 180;
+
+/** Convert azimuth clockwise from north and altitude above the horizon to a unit ENU vector. */
+export function azAltToVec(az, alt) {
+  const a = rad(az), e = rad(alt), ce = Math.cos(e);
+  return [ce * Math.sin(a), ce * Math.cos(a), Math.sin(e)];
+}
+
+/** Convert an east/north/up vector to azimuth clockwise from north and altitude. */
+export function vecToAzAlt(vector) {
+  const [east, north, up] = vector;
+  const horizontal = Math.hypot(east, north);
+  return { az: wrap360(deg(Math.atan2(east, north))), alt: deg(Math.atan2(up, horizontal)) };
+}
+
+/** Quaternion [x,y,z,w] conjugate. */
+export function quatConj([x, y, z, w]) {
+  return [-x, -y, -z, w];
+}
+
+/** Rotate a 3D vector by quaternion [x,y,z,w]. */
+export function quatRotate([x, y, z, w], [vx, vy, vz]) {
+  const tx = 2 * (y * vz - z * vy);
+  const ty = 2 * (z * vx - x * vz);
+  const tz = 2 * (x * vy - y * vx);
+  return [
+    vx + w * tx + (y * tz - z * ty),
+    vy + w * ty + (z * tx - x * tz),
+    vz + w * tz + (x * ty - y * tx),
+  ];
+}
+
+/** Great-circle angular separation of two azimuth/altitude positions, in degrees. */
+export function angularSeparation(az1, alt1, az2, alt2) {
+  const a1 = rad(alt1), a2 = rad(alt2), da = rad(wrap180(az2 - az1));
+  const cosSep = Math.sin(a1) * Math.sin(a2) + Math.cos(a1) * Math.cos(a2) * Math.cos(da);
+  return deg(Math.acos(Math.max(-1, Math.min(1, cosSep))));
+}

lib/stars.mjs

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+// Bright-star catalogue: J2000 right ascension (hours) and declination (degrees).
+// Values are approximate and intended for telescope target selection, not astrometry.
+export const STARS = {
+  sirius: { label: 'Sirius', ra: 6.75248, dec: -16.7161 },
+  canopus: { label: 'Canopus', ra: 6.39920, dec: -52.6957 },
+  arcturus: { label: 'Arcturus', ra: 14.26102, dec: 19.1825 },
+  vega: { label: 'Vega', ra: 18.61565, dec: 38.7837 },
+  capella: { label: 'Capella', ra: 5.27816, dec: 45.9980 },
+  rigel: { label: 'Rigel', ra: 5.24230, dec: -8.2016 },
+  procyon: { label: 'Procyon', ra: 7.65503, dec: 5.2250 },
+  betelgeuse: { label: 'Betelgeuse', ra: 5.91953, dec: 7.4071 },
+  achernar: { label: 'Achernar', ra: 1.62857, dec: -57.2368 },
+  hadar: { label: 'Hadar', ra: 14.06373, dec: -60.3730 },
+  altair: { label: 'Altair', ra: 19.84639, dec: 8.8683 },
+  acrux: { label: 'Acrux', ra: 12.44330, dec: -63.0991 },
+  aldebaran: { label: 'Aldebaran', ra: 4.59868, dec: 16.5093 },
+  antares: { label: 'Antares', ra: 16.49013, dec: -26.4320 },
+  spica: { label: 'Spica', ra: 13.41988, dec: -11.1613 },
+  pollux: { label: 'Pollux', ra: 7.75526, dec: 28.0262 },
+  regulus: { label: 'Regulus', ra: 10.13953, dec: 11.9672 },
+  deneb: { label: 'Deneb', ra: 20.69053, dec: 45.2803 },
+  polaris: { label: 'Polaris', ra: 2.53030, dec: 89.2641 },
+  castor: { label: 'Castor', ra: 7.57667, dec: 31.8883 },
+};