Personal Sky: Data-Driven Astrology App

Personal Sky is a data-driven astrology browser app that lets you search your chart and talk with your sky. It uses an accurate ephemeris, a deterministic PHP data interpretation layer, and only then does the AI do its interpretation pass, keeping the conversation grounded in the calculated facts of the chart.

The Problem

Most astrology apps either oversimplify (daily horoscope generators) or let an LLM freestyle with no grounding in actual astronomical data. I wanted to build something where every claim the AI makes is backed by a real, calculated chart position, and where the app works perfectly well without AI at all.

What I Built

Ephemeris-Driven Chart Engine

Birth place and time are resolved into coordinates and timezone data. PHP builds and validates the natal chart, current transits, houses, aspects and geometric patterns from ephemeris data. Unknown birth times automatically disable houses and angles, so the app never shows data it can't verify.

Interactive SVG Chart

The natal and present-day transit charts are overlaid in a fully interactive SVG wheel. You can explore planets, aspects, houses and patterns directly.

AI Grounded in Calculated Facts

The verified chart context is selectively passed to Claude, so the model explains calculated facts rather than inventing them. A deterministic fallback works without AI for users who prefer it.

Sky Passport subscriptions

Personal Sky is live in beta. Visitors can explore their chart and ask up to 5 free questions; Sky Passport costs £3/month and adds unlimited follow-up questions, saved charts, and access across devices.

Collaboration

Built in collaboration with astrologer Kelfin Oberon, who designed the astrological structure and interpretation framework that the deterministic layer implements.

The Stack

PHP, JavaScript, SVG, Claude API, Stripe. Originally launched through Ffilm.org, now live at PersonalSky.net.

Visit at personalsky.net

Originally posted on Contra: https://contra.com/p/B2OlkMBX-personal-sky-data-driven-astrology-app