findPassesfunction

Every pass of the satellites over a place in a span of time, the ones a person can see or all of them. For each satellite the search steps through the span every 30 seconds, then narrows each rise, highest point and set to a tenth of a second; for each pass it works out where the satellite is lit by the Sun, how dark the watcher's sky is, and how bright the satellite looks. It needs satellite.js (MIT, an optional peer dependency) and imports in a browser or on a server. It is for satellites that rise and set within hours (low orbits); one that stays above the horizon (a geostationary one) has no passes.

Passes depend on fresh elements: SGP4's error grows by about a second of time a day or two for the ISS, and a reboost (the ISS has one every month or two) moves the station by more than that all at once, so a pass is as good as the elements are new. Each pass says how old they are (elementAgeDays) and flags stale after two weeks.

import { findPasses } from "@johnmorrisdotca/chikyu-earth/passes";

function findPasses(sets: ElementSet | readonly ElementSet[], observer: Observer, window: PassWindow, options?: PassOptions): SatellitePass[]

import { findPasses } from "@johnmorrisdotca/chikyu-earth/passes";

const iss = {
  OBJECT_NAME: "ISS (ZARYA)",
  OBJECT_ID: "1998-067A",
  EPOCH: "2026-11-02T10:25:21.580320",
  MEAN_MOTION: 15.49150046,
  ECCENTRICITY: 0.0007139,
  INCLINATION: 51.6332,
  RA_OF_ASC_NODE: 335.9757,
  ARG_OF_PERICENTER: 339.3739,
  MEAN_ANOMALY: 20.6961,
  NORAD_CAT_ID: 25544,
  BSTAR: 0.00012,
  MEAN_MOTION_DOT: 0.0001,
  MEAN_MOTION_DDOT: 0,
};
const day = Date.UTC(2026, 10, 3);
const passes = findPasses(iss, { latitude: 51.5, longitude: -0.13 }, { from: day, to: day + 5 * 86_400_000 }, { all: true });
console.log(passes.length > 0, passes[0]?.highest.compass);

true S