How it works
Methodology
The Astro Diary is built on real astronomical calculations and a language model that never invents planetary positions. This page documents the whole stack so you can decide whether to trust it.
Ephemeris source
Every planetary position is computed from real astronomy — the same positions professional astrologers and academic astronomy tools use. We host it on our own API at astroapi.ideasallday.com so all chart traffic stays server-side and the ephemeris data set is versioned. No fake positions. No 'close enough' approximations. If the sky says Mars is at 12° Scorpio, our chart says Mars is at 12° Scorpio.
House system
The default is Placidus — the most widely used system in modern Western astrology. In Settings you can switch to Whole Sign, Koch, Regiomontanus, Campanus, Equal, or Alcabitius. If your birth time is unknown, we fall back to a noon-UT solar chart and hide every house or Ascendant reference in the UI and the LLM prompts. Faked precision is worse than no precision.
Tropical vs. sidereal
The default is tropical — the seasonal zodiac used by most Western astrology. You can switch to sidereal in Settings with a choice of ayanamsa (Lahiri, Fagan-Bradley, Raman, Krishnamurti). The chart, the transits, the timeline, the report — everything follows your setting so you never mix frameworks by accident.
Orb factor
Aspects have wiggle room — a trine that's exact to the arc-second is stronger than one that's 5° off. Our default orb factor is 1.0, which is standard for modern astrology. You can tighten it to 0.5 (only tight aspects, for the traditionalists) or loosen it to 1.5 (more aspects, more texture). Under about 1° of orb we mark an aspect TIGHT; 1-3° is moderate; 3-8° is wide for the majors.
What the chat can do
The AstroBuddy chat reads your real chart. It has tool-scoped access to your own natal chart, current transits, life-stage cycle, active goals, and journal entries you've written. Every answer is grounded in that data — the tools are locked to the current user, so the model can never read someone else's chart. When you ask 'why is this Mars square hitting me so hard?' the answer is based on your actual Mars, not a generic template.
What the chat won't do
No predicting fixed future events. No medical, legal, or financial advice. No sun-sign horoscopes ('Aries, your week…'). No mystical claims about your fate. Every reading is framed as structure versus event: the sky shows the terrain you're on, not the outcome you'll hit. If you push it toward fortune-telling, it'll politely refuse.
The language model
We don't name the underlying model in user-facing surfaces — that's plumbing, not the product — but for the curious: readings are generated by the Anthropic Claude family (Sonnet 4.6 for the full report, Haiku 4.5 for fast composers like the daily digest). We route through the Vercel AI Gateway so the app can fail over to a backup provider if one is degraded.
Privacy invariants
Journal entries are encrypted at rest with a server-held key — even if someone with database access reads a row, the entry content is unreadable without the key. The LLM tools are owner-scoped: the userId is captured in a closure at request time, so the chat can never see another user's chart or journal. The ephemeris API key never reaches the browser. We don't sell, share, or resell user data — ever.
Extended body support
Every chart includes the seven traditional planets, the outer planets (Uranus, Neptune, Pluto), Chiron, the lunar nodes (mean and true), and five asteroids: Ceres, Pallas, Juno, Vesta, and Lilith. Reading your chart shouldn't require paying to unlock the parts pop-astrology treats as premium.
What we deliberately don't do
No sun-sign horoscopes. No Vedic mode (the tone is wrong for our brand). No Human Design (IP-encumbered). No tarot or i-ching. No celebrity-chart voyeurism. If you want any of those, other apps do them well; this one is for people who want the geometry of their own chart taken seriously.
Bugs and questions
If a position or aspect looks wrong to you, that's a bug — the calculation is deterministic and we cache canonical charts by SHA-256 of the birth-data tuple, so two people with the same input get the same output. Email hello@ideasallday.com with your birth data and the surface where the wrong value appeared.