Methodology and transparency
How Zodiaro calculates a birth chart
Zodiaro separates the astronomical calculation from the astrological interpretation. This page documents the inputs, coordinate choices, ephemeris, house system, unknown-time policy, privacy behavior, and limits behind the public tools.
- Swiss Ephemeris
- IANA timezones
- Tropical zodiac
- Placidus houses
The direct answer
What calculation does Zodiaro perform?
For a timed chart, Zodiaro converts the recorded local birth moment to UTC with the selected place’s historical timezone, computes geocentric planetary longitudes with Swiss Ephemeris, maps those longitudes to the tropical zodiac, and calculates the Ascendant, Midheaven, and Placidus house cusps from the birth coordinates. It then measures aspects and assigns planets to houses.
Inputs
Why date, time, and place do different jobs
A birth date is enough for many slow-moving sign placements. The local time and coordinates are what turn a date-level sky into a chart with a local horizon and houses.
- 01
Birth date
Locates the planetary positions for that day and year.
- 02
Recorded local time
Determines the exact UTC moment and fast-moving chart angles. The Ascendant moves roughly one degree every four minutes on average, with variation by latitude and sign.
- 03
Birthplace
Supplies latitude, longitude, and the timezone used for the historical local-to-UTC conversion.
Declared settings
The conventions behind the result
Another calculator may use different conventions. Compare these settings before assuming one output is wrong.
| Setting | Zodiaro choice | What it affects |
|---|---|---|
| Zodiac | Tropical; no ayanamsa | The 30-degree sign sectors begin at the March equinox point. |
| Ephemeris | Swiss Ephemeris | Planetary longitude, motion, and calculated points. |
| House system | Placidus | House cusps and the house assigned to each placement. |
| Lunar node | True North Node | The nodal degree includes its short-period oscillation; the South Node is exactly opposite. |
| Timezone | IANA timezone for the selected coordinates | Historical daylight-saving and offset rules used to obtain UTC. |
Unknown-time policy
We withhold what the input cannot support.
When a user marks the birth time unknown, Zodiaro calculates date-level planetary positions from a noon reference and does not present a Rising sign or houses. If the Moon or another placement is close to a sign boundary, the result should be treated as time-sensitive.
Why we do not default to midnight
A silent midnight or noon assumption can look exact while being false. Noon is used only as a clearly disclosed reference for the date-level planet map; time-dependent fields remain absent.
What a rounded time changes
A rounded time can move the Ascendant degree, shift a nearby house cusp, or change the Rising sign. The complete report includes a time-sensitivity view around the recorded moment.
Interpretation policy
Specific language, visible uncertainty
The chart positions are calculations; astrological meanings are interpretive traditions. Zodiaro describes patterns as possibilities and reflection prompts, not as diagnoses, facts about character, or guaranteed future events.
Editorial safeguards
- Distinguish calculation from interpretation.
- State unknown-time and boundary limitations.
- Avoid deterministic claims about health, money, law, safety, or relationships.
- Keep visible explanations consistent with structured data.
- Correct factual or technical errors when they are identified.
Privacy and storage
Public focused calculators do not create a saved profile.
Focused calculator inputs are processed for the requested result and are not saved by those tools. A complete chart result uses an opaque, short-lived identifier so the result can be opened without exposing birth details in the URL.
If a user later chooses an account feature, the account experience should explain what is saved and expose export and deletion controls. Privacy behavior is a product rule, not a marketing phrase.
Read the privacy policyPrimary technical references
Sources behind the calculation layer
These sources document the astronomical and timezone mechanisms. They do not validate astrological interpretation as science.
- Swiss Ephemeris programmer documentation — AstrodienstPlanetary calculations, flags, houses, and supported points.
- Time Zone Database — IANACurrent and historical civil-time rules used by timezone software.
- Planetary ephemeris export information — NASA JPLBackground on numerical planetary ephemerides and state-vector data.
See the method in use