Look up tonight. Free, plain-language times for when the International Space Station and China's Tiangong station are visible from where you stand: when to step outside, which way to face, how high it climbs, how bright it is, how long it lasts.
https://skypassalert.com · Status: Phase 2, a live preview for Fremont, CA. Place search, Chinese and sharing arrive in v0.1. See docs/ROADMAP.md and docs/STATUS.md.
- No app, no account, no ads, no cookies, no personal data. Geolocation, if you allow it, stays on your device.
- English and 简体中文 at launch.
- Open source, with a published accuracy report: docs/accuracy/phase2.md. It is generated in CI against Skyfield; satellite positions agree to within 15 m.
Develop
Requires Node 22+.
npm install
npm run dev # local dev server
npm test # unit tests (Vitest)
npm run ci # lint, format check, typecheck, tests, build, JS budget
npm run lighthouse # Lighthouse CI against a production preview (needs Chrome)
npm run lab:seasons # "predict, then run" labs: sidereal, shadow, pass, seasons
npm run accuracy # compare the engine with validation/reference/reference.json
To regenerate the Skyfield reference locally: python3 -m venv .venv && .venv/bin/pip install -r validation/requirements.txt && npm run reference.
| Path | What |
|---|---|
src/engine/ |
framework-free prediction math (time, frames, Sun/Moon/planets, shadow, passes) |
src/ui/, src/pages/ |
the screen (design rules in docs/DESIGN.md) |
validation/ |
Skyfield reference generator for the accuracy harness |
public/data/, data/archive/ |
orbital elements we serve, and every fetch we've archived |
src/ |
React UI |
scripts/ |
build-time generators and checks |
docs/ |
product, architecture, decisions, roadmap, learning chapters, growth kit |
Start reading at CLAUDE.md, then docs/PRODUCT.md and docs/learn/00-start-here.md.
Accuracy and safety
Predictions are estimates for sky-watching. They are not for safety-critical use. Every prediction will show how old its orbital data is.
Data and credits
Orbital elements and Earth-orientation data: CelesTrak. Planet elements: JPL. Fremont's coordinates: GeoNames (CC BY 4.0). Full list: ASSETS.md.
How this was built
Designed and directed by Ishaan, a high-school student in Fremont, CA, who sets direction, reviews every change, and checks the predictions against real passes outdoors. Implemented with Claude Code.
