Astrodynamics

Open the tool

Why and how it was built

Astrodynamics was built with Claude as the primary implementer, working from Matthew’s design brief and review. Its ephemeris core is checked the way a mathematician checks a proof: computed planetary positions are validated against Swiss Ephemeris via a Python oracle, and the asteroid data — Chebyshev packs fitted to JPL Horizons — is tested against samples held out from the fit, not just the training data, before anything ships. Everything runs client-side: charts, saved data, and interpretations never leave the browser, an explicit design constraint rather than an afterthought. The interpretation layer offers four distinct written voices for the same chart, backed by a human-in-the-loop authoring pipeline where draft texts get reviewed and refined rather than generated fresh each time. It’s a working demonstration of AI-assisted engineering held to the same evidentiary standard as the rest of Matthew’s work: don’t claim it’s right, check it against ground truth.

Overview

Astrodynamics is a local-first astrology application: accurate offline chart calculation (planets, Pluto, Chiron, Ceres, Pallas, Juno, Vesta, Eris), interactive SVG chart wheels and bi-wheels, Placidus houses, transits, synastry, and midpoint composites. Charts are saved locally and interpreted in four switchable styles (Psychological, Mundane, Energy, Minimal) with a plain-language glossary. It installs as a PWA and works fully offline after the second visit — no server, no accounts, nothing leaves the device.

Key Features

  • Offline ephemeris — planetary positions (Sun–Pluto plus the four major asteroids, Chiron and Eris) computed locally via astronomy-engine and Chebyshev packs, checked against Swiss Ephemeris and held-out JPL Horizons data
  • Full chart maths — Placidus houses, aspects, transits, synastry, and Ebertin midpoint composites
  • Interactive wheels — tunable SVG glyph kit for chart wheels and bi-wheels
  • Four interpretation voices — Psychological, Mundane, Energy, and Minimal readings of the same chart, with a plain-language glossary and AI-snapshot export
  • Retrograde orrery — an animated view of the planets, Mercury to Pluto, against the zodiac: exact stations (matching Swiss Ephemeris), retrograde arcs, oppositions and conjunctions, sidereal against synodic periods, and the Venus pentagrams; distances true to scale out to Mars and logarithmic beyond; light or dark; also on its own page
  • Installable PWA — offline after the first load; no server, no accounts, no data leaves the device

Status

Milestones M1–M4 are built; the interpretation content pipeline is the current work. Built with Svelte 5, TypeScript, and Vite; npm test runs the golden test suite against Swiss Ephemeris and held-out JPL Horizons references. The build embeds its own ephemeris data (ephemeris packs, gazetteer, text packs), so the deployed copy below runs and works fully offline without a server — it is a static export of npm run build, not a live service.