A desktop stargazing app for Windows, macOS and Linux. It draws the real sky above your location at any moment in time, tells you what you are looking at, and works without a network connection.
The sky map is the main screen. It draws 8,920 naked-eye stars, another 74,559 telescopic ones whose density is what you see as the Milky Way, all 88 constellation figures, the Sun, Moon and planets, 1,314 deep-sky objects at their catalogued size and shape, 17 black holes, and satellites if you switch them on. You move around with the mouse, the trackpad or the keyboard.
Behind all of that sits a photograph of the whole sky, aligned by converting each view direction into galactic coordinates. Zoom in far enough on a nebula or a galaxy and the app fetches a real survey image of it and puts it in place at the right size and angle. The catalogue stars land on the stars in the photograph, which is how you can tell it went in the right place.
Keep zooming and the planets stop being dots. Each one becomes a lit sphere carrying its real surface map, at its true apparent size, showing the phase it is actually in. The Moon shows the near side with its libration, Jupiter shows its cloud bands, and Saturn's rings are a real annulus in the planet's equatorial plane rather than a drawn ellipse.
Search finds anything by name, Bayer letter or catalogue number. Select it and you get altitude, azimuth, magnitude, distance, rise and set times, when it is best placed tonight, a short explanation of what it actually is, and links out to NASA, Wikipedia and SIMBAD.
The Time Machine sets the sky to any date, past or future, and will run time forward at up to a month per second. Visible Tonight tells you what is worth going outside for from where you are, checked against tonight's real dark window rather than the clock. Events covers eclipses, meteor showers, conjunctions, oppositions, lunar phases and the solstices, and says for each one whether you can see it from your location.
Beginner mode strips the sky back to the bright, well-known objects. The Learn screen has guided activities that only complete when you actually find the thing on the map, plus quizzes and progress stored on your machine.
Everything except satellite tracking works offline, because every catalogue ships inside the app. Wherever a number appears, the interface says whether it was calculated, read from a catalogue, downloaded, or reused from cache.
Installers for all three platforms are attached to the
latest release: a .dmg
and a .zip for macOS, an installer and a portable build for Windows, an AppImage and a
.deb for Linux.
None of them are signed, since there is no Apple or Microsoft certificate behind this. On macOS you have to right-click and choose Open the first time, and Windows SmartScreen will complain. The macOS builds are Apple silicon only, so an Intel Mac needs a local build.
- Node.js 20 or newer
- npm 10 or newer
- A C toolchain, for the one native dependency (
better-sqlite3). Xcode Command Line Tools on macOS, the Visual Studio Build Tools on Windows,build-essentialandpython3on Linux. If it will not build, the app falls back to a JSON file store and says so in Settings. Nothing else changes.
npm installnpm run data:buildThe second step downloads the source catalogues once, about 38 MB, and reduces them to
the 8 MB or so that ships inside the app in resources/data. Downloads are cached in
.data-cache/, so running it again is cheap. The app will not start until you have done
this. If the files are missing it says so and points you here.
There is one application and two ways to start it. You never launch Electron by itself. Electron is the runtime the app is built on, in the same way a Java app runs on the JVM.
For development, with hot reload:
npm run devmacOS shows this in the Dock as Electron rather than NovaSky, because it is running inside the generic development binary. That is expected. It is the same app.
To actually use it, build the packaged app once and open it like anything else:
npm run pack:macopen release/mac-arm64/NovaSky.appThat one has the right name and icon and needs no terminal.
Two more that are occasionally useful. npm run build type-checks both projects and
writes a production bundle to out/. npm start runs that bundle without packaging it.
npm run icon regenerates build/icon.png, the single source image electron-builder
turns into the icon sets for all three platforms.
npm run pack:macnpm run pack:winnpm run pack:linuxOutput lands in release/, with the unpacked .app in release/mac-arm64/ (or
release/mac/ on Intel). You also get a .dmg and a .zip on macOS, an NSIS installer
and a portable .exe on Windows, an AppImage and a .deb on Linux.
The JavaScript cross-compiles fine, but better-sqlite3 is native, so build each
platform's installer on that platform or let CI do it. Otherwise the binding will not
match.
npm test163 tests. The astronomy ones check coordinate transforms against astronomy-engine's own routines, rise and set times against known geometry, eclipse and meteor-shower dates against published values, and SGP4 against real ISS elements. The renderer ones check the galactic rotation against Sagittarius A* and the north galactic pole, and where survey cutouts land and which way up they are. The rest cover the Content Security Policy and the UI: search, the Time Machine, onboarding, the details panel, and accessibility roles.
npm run typechecknpm run offlineThe last one boots the built app with every outbound request refused and checks the sky map still renders. Working with no network is the whole point of the app, so it gets its own test. It also reports how many requests were attempted, and the answer should be zero.
| Key | Action |
|---|---|
T |
Open the Time Machine |
S |
Focus search |
B |
Toggle beginner mode |
F |
Toggle fullscreen |
Esc |
Close panels |
| Arrow keys | Look around the sky |
+ / - |
Zoom in and out |
0 |
Reset the view |
novasky/
├── .github/workflows/ # CI: type-check, test, build and boot on all three OSes
├── scripts/build-data.mjs # downloads and reduces the source catalogues
├── resources/data/ # the offline catalogues that ship with the app
├── src/
│ ├── main/ # Electron main: window, storage, network, notifications
│ ├── preload/ # the single, audited bridge into the renderer
│ ├── renderer/ # React UI and the Three.js sky map
│ └── shared/ # astronomy, catalogue model and types, used by both
├── tests/ # astronomy, renderer geometry, CSP and UI tests
└── docs/ # data sources, design, and how to extend the app
src/shared imports nothing from Electron and nothing from the DOM, so every
astronomical calculation is testable on its own and usable from either process.
There are no accounts and no telemetry of any kind. Your location, settings and learning progress live in a SQLite database inside the app's own data directory on your machine. The only request the app ever makes on its own is to CelesTrak for satellite orbital elements, and you can switch that off in Settings. Settings also has buttons for clearing cached downloads and for erasing everything the app has stored.
MIT for the code. The bundled catalogues and imagery are other people's work and keep their own licences, listed in docs/DATA_SOURCES.md and summarised in LICENSE.
Written by Sam Gabriel, with Claude (Anthropic) as a pair programmer.