How Galaxia computes your chart
Every chart on Galaxia is computed from real sky positions. This page publishes the method: what we calculate, what we omit, how orbs work, how birth precision limits the chart, and how written readings differ from Vela.
What a chart can and cannot do
A birth chart describes how someone is built. It does not predict events, choices, or outcomes.
It cannot tell you whether to stay in a relationship, who was at fault, or what will happen next month.
Without a birth time, a Rising sign and house placements cannot be computed honestly, and Galaxia will not invent them.
Birth precision
Year-only charts compute the Sun and the outer planets Uranus, Neptune, and Pluto only. Inner planets and the True Node are omitted because their signs depend on a day we do not know. Natal aspects are not computed for year-only data.
Date-only charts compute the standard set of bodies at noon UTC on that calendar date. Houses, the Ascendant, and the Midheaven are not shown because birth time and place are missing.
Exact charts use local birth time converted to UTC with the birth place timezone. Houses and angles are computed only when latitude and longitude are known.
Ephemeris source
Sun through Pluto use astronomy-engine, an open-source MIT library of published planetary theory. Positions are geocentric ecliptic longitudes in the tropical zodiac, not AI-generated.
The True Node is computed on date-only and exact charts from the geocentric Moon state (osculating node). Mean Node is not computed.
Chiron is computed when the birth date falls in the 1900 through 2101 range covered by our table. Positions come from JPL Horizons samples with ten-day linear interpolation, not from astronomy-engine. Chiron synastry readings are authored for Compare; natal Chiron sign and house copy is not authored yet.
House system
Houses are twelve life arenas: where a placement tends to show up. Mars in a partnership house and Mars in a work house are the same planet in different rooms.
Galaxia's default is Placidus, the time-based system used on many reference chart sites. House sizes are uneven because they follow how the sky rises at that latitude.
You can switch to Whole Sign or Equal House in settings. Those choices are computed, not relabeled. If Placidus is undefined at a polar birth latitude, we show Whole Sign and say so.
Aspect orbs
An orb is how far an angle can drift from exact and still count as that aspect. Galaxia uses one allowance per aspect type for every body. The Sun and Moon do not get a wider window than Saturn.
| Aspect | Orb (°) |
|---|---|
| Conjunction | 8° |
| Sextile | 4° |
| Square | 6° |
| Trine | 6° |
| Opposition | 8° |
| Quincunx | 2.5° |
A transiting Moon is capped at 3°, because it moves too fast for the wider natal allowance to stay meaningful.
Applying and separating
Applying means the exact contact is still ahead. Separating means it has already passed. Exact means the angle is already there.
Galaxia computes this for transits. We estimate the UTC instant of exact contact from the transiting body's motion, then compare that instant to now. Within 0.05° of exact, or about one hour of that instant, the phase is exact.
Natal and synastry aspects also mark applying or separating from each planet's longitude speed at the birth moment. If that speed is missing, the phase is left blank rather than guessed.
How readings are written
Placement and aspect copy is written in advance and stored in the codebase before anyone opens the app. A reading pulls that stored copy; it is not generated on the fly for each person.
Each reading is reviewed and approved by the founder before it ships.
Not every natal aspect pair has a written reading. Pairs we have not authored are not shown rather than filled in with generic text.
Today 38 of 270 possible natal aspect pairs have a written reading in the library.
Curated interpretation library
Pair-specific readings are hand-written and static. The engine computes aspects; it does not invent copy for a missing cell.
Natal aspect readings (Sun through Pluto, six aspect types including quincunx): 38 of 270 cells authored. Unauthored cells are omitted from Key aspects rather than filled with generic text.
Synastry readings in the compare library: 330 of 330 cells authored across 66 unordered pairs (five major aspects each; quincunx uses type-only copy).
Chiron synastry (Chiron with each of eleven bodies, five major aspects): 55 of 55 cells authored.
What Vela does
Vela is the in-app guide powered by Anthropic's Claude. Its replies are generated, unlike the written readings above.
Vela receives computed chart facts and a list of aspects from your stored charts. It is instructed to name only aspects from that list, never to invent placements, and not to predict the future.
Vela can be wrong or incomplete like any AI. Treat it as guidance grounded in your chart data, not as a final authority.
What we test against
House cusp calculation is checked against a published Placidus reference chart to within about one arcminute. We do not claim a universal match to every external ephemeris for every chart.
What we do not compute
We compute the Sun through Pluto, the True Node on date and exact charts, and Chiron when our table covers the date. We use the five major aspects plus the quincunx on natal and synastry charts, tropical signs, and retrograde flags. Transits, daily notes, and Vela aspect lists stay on the five majors. We do not compute the rest of a professional ephemeris chart, and we do not pretend those points are present.
- Mean Node
- Black Moon Lilith
- Asteroids
- Minor aspects other than the quincunx (semisextile, semisquare, sesquiquadrate)
- Arabic parts, including the Part of Fortune
- Vertex and midpoints
- Sidereal zodiac