Methods and models · ChronOS guide
Astronomical calculations: from civil time to celestial coordinates
Astronomical calculation is a pipeline. Civil input is resolved to an exact instant, converted into the required time scales, evaluated with a planetary model and transformed into the requested coordinate system. Each stage introduces conventions that should be named in the result.
01 / Method
The calculation pipeline
UTC is convenient for users, but orbital and Earth-rotation calculations require additional time scales. Julian dates provide a continuous numerical representation, while TT, UT1 and TDB serve different parts of the model. Precession, nutation, aberration and observer position then affect how a computed vector is expressed.
ChronOS keeps the astronomical state separate from higher-level chart and tradition models. This makes the underlying position reusable and makes domain-specific conventions visible.
- Calendar and timezone resolution
- UTC, UT1, TT and TDB conversion
- Ephemeris evaluation
- Precession, nutation and coordinate transformation
- Optional observer and domain-specific transformations
02 / API example
Calculate a reproducible astronomical state
Pin the instant, selected bodies and profile so the request can be repeated and compared across releases.
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
How calculations should be validated
Validation should cover reference values, difficult dates, model boundaries and invariants such as normalized angular ranges. A comparison against one external engine is useful evidence, but it does not prove universal accuracy because different systems may select different time, precession or reference-frame conventions.
ChronOS exposes release-specific evidence and documents known limitations so differences can be classified instead of hidden.
04 / Applications
Calculations available above the position layer
Once the celestial state is established, typed operations can calculate charts, aspects, events, lunar sectors, timelines and renderable outputs.
- Planet positions and velocities
- Houses and angles
- Aspects, stations and ingresses
- Lunar sectors and phases
- Calendar and solar-time conversions
05 / FAQ
Frequently asked questions
Why are multiple time scales necessary?+
Civil time, Earth rotation and dynamical orbital models do not use one interchangeable clock. Explicit scales prevent hidden offsets and make a result interpretable.
What is the difference between geometric and apparent position?+
A geometric position represents the modeled body geometry, while an apparent position applies observational corrections defined by the selected model and reference frame.
Are astronomical and astrological calculations the same?+
Astrology applications consume astronomical positions but add chart, zodiac, house and interpretive conventions. ChronOS models those layers separately.