Moon Phase

A Pebble Alloy watchapp for Pebble Time 2 (Emery) that shows tonight's moon phase: the current phase name, illumination percentage, and a moon disc rendered procedurally (no image assets) whose lit/dark terminator is drawn to match the real phase.

The phase is computed entirely on the watch (Jean Meeus, Astronomical Algorithms 2nd ed., ch. 49 / Table 49.A). The New/Full events use the leading periodic terms; the Quarters use the full 25-term correction series plus the W term — phase timing is typically accurate to within a couple of minutes, far tighter than this app's display resolution. The value is anchored to 9 PM local time so it reflects that evening's phase specifically. It is recomputed every time you open the app, and you can press the middle (select) button to recompute on demand.

The correction series are written as flat arithmetic rather than coefficient arrays on purpose: this device gives the watch-side JavaScript only ~120 KB of heap, and the array form overflowed it at module load.

There is no network call. An earlier version also confirmed/upgraded the local value against the USNO Moon Phase API in the background, but that fetch reliably crashed the watch with an out-of-memory abort — reproduced on both the QEMU emulator and physical hardware, across several memory-optimization attempts, and confirmed by removing the fetch entirely and watching the crash disappear (clean heap usage log, proper teardown, Still allocated 0B, on a real Pebble Time 2). See git history for that investigation if you want to revisit it; this device's JS heap is only ~120KB, and fetching HTTPS from it was not reliable enough to ship.

Building & running

Common workflows are wired up as package.json scripts:

npm run build            # pebble build
npm run rebuild          # pebble clean && pebble build
npm start                # build, then install on the emery emulator
npm run install:emulator # install on the emery emulator
npm run logs             # tail emulator logs
npm run screenshot       # capture the emulator screen -> screenshots/emery.png
npm run kill             # stop running emulators

npm run install:phone -- <ip>            # install to a paired phone (IP from
                                         # Settings > Developer Connection)

npm run art              # regenerate store/marketing/ composites

npm run release -- fix    # bump patch, commit + tag, publish, push
npm run release -- minor  # bump minor  ·  also: major

npm run release builds, runs npm version (which commits + tags), then pebble publish, then git push --follow-tags. It uploads the release without making it public — add PUBLISH=1 to publish live, and RELEASE_NOTES="…" to set the notes. Must be run from a clean main. See store/README.md for the appstore details.

Or run the raw commands directly — pebble build, pebble install --emulator emery, pebble install --phone <ip>.

Target platforms

emery (Pebble Time 2) only. The layout assumes a rectangular display, so the round platform (gabbro) is not built or supported.

Project layout

src/c/mdbl.c                   C glue around the Moddable runtime
src/embeddedjs/main.js         JavaScript that runs on the watch
src/embeddedjs/manifest.json   Moddable manifest
src/pkjs/index.js              PebbleKit JS (phone-side) code
package.json                   Project metadata (UUID, platforms, resources) + npm scripts
scripts/release.sh             Version bump + publish + push (npm run release)
store/                         Appstore icons, screenshots, marketing art, submission notes
wscript                        Build rules — usually no need to edit

Documentation

Full SDK docs and tutorials: https://developer.repebble.com