Astronomical computation · ChronOS guide
Ephemeris calculations for auditable celestial software
An ephemeris describes where celestial bodies are at a specified time. ChronOS exposes that calculation as a versioned engine and hosted API, returning positions together with the time scale, reference frame, dataset and model information needed to interpret the result.
01 / Method
What an ephemeris calculation contains
A useful ephemeris result is more than a longitude. The input instant must be normalized to explicit time scales, evaluated against a defined astronomical dataset and expressed in a named coordinate frame. Apparent and geometric positions, observer location and sidereal reference choices are different contracts and must not be silently mixed.
ChronOS treats those choices as calculation inputs or profile settings. The returned metadata identifies the engine and dataset versions so the same request can be investigated when models evolve.
- UTC and dynamical-time handling
- Geocentric, topocentric and heliocentric coordinate choices
- Position, velocity and motion state
- Versioned model and dataset provenance
02 / API example
Request an exact-instant ephemeris
The canonical v2 endpoint accepts an ISO 8601 UTC instant, an optional body selection and an immutable calculation profile reference.
curl --request POST \
--url https://api.chronos-ephemeris.com/v2/ephemeris \
--header "Authorization: Bearer $CHRONOS_API_KEY" \
--header "Content-Type: application/json" \
--data '{
"datetime_utc": "2026-07-16T12:00:00Z",
"bodies": ["sun", "moon", "mercury", "venus", "mars"],
"profile": "chronos.standard@1"
}'Keep API keys in server-side secret storage. The example uses an environment variable and contains no production credential.
03 / Evidence
Precision and performance are separate claims
Numerical agreement and request latency answer different questions. ChronOS publishes its validation models and versioned evidence through the Validation Center. Performance results are identified as baselines for a particular release and environment rather than universal speed guarantees.
Applications should pin a calculation profile, retain result provenance and validate the specific bodies, dates and coordinate options that matter to their own use case.
04 / Applications
Where ephemeris data is used
The same astronomical state can support planetarium views, calendars, educational tools, research visualizations and astrology applications. Domain-specific interpretation belongs above the measurable ephemeris layer.
- Planetary position tables and timelines
- Natal, transit and return charts
- Celestial event searches
- Scientific and educational visualization
05 / FAQ
Frequently asked questions
What is an ephemeris?+
An ephemeris is a table or computation that gives the predicted position of celestial bodies for specified times under a defined astronomical model.
Does ChronOS work as an offline ephemeris?+
ChronOS is available as a hosted API and has compatible native-runtime paths. Availability and licensing depend on the selected product plan and platform.
What time format does the ChronOS API accept?+
The canonical ephemeris request accepts an explicit ISO 8601 UTC timestamp and returns time and provenance metadata with the result.