Calculation Transparency
If the position of the stars is off, everything downstream is off.
The foundation of any astrology reading is a single fact: where the stars were at that exact moment. If that's even slightly wrong, the signs, houses, aspects, and every interpretation built on them go wrong too. Coelo computes that foundation with an in-house engine built for as much precision as we can achieve.
Our calculation engine
Built in-house
Most astrology apps embed an existing calculation library. Coelo implements everything ourselves, from reading the raw ephemeris data to computing the positions of celestial bodies. That's why nothing is a black box.
NASA/JPL's high-precision ephemeris DE441
We read DE441 directly — the dataset published by NASA's Jet Propulsion Laboratory (JPL) covering the motion of bodies in the solar system. It's the same kind of foundational data used by space agencies worldwide for mission planning.
Precision to the international standard (ERFA)
Astronomical corrections such as precession, nutation, and aberration are computed with an implementation that conforms to the calculation procedures standardized by the International Astronomical Union (IAU). We verify our results against international reference values to within 0.001 arcseconds (1/3,600,000 of a degree).
No external calculation libraries
We do not use the third-party astrology calculation libraries that power most other astrology software (we reference them only as comparison data during verification, never at runtime). We can be this open about our calculations because we understand every part of them ourselves.
Computed on your device (privacy)
Our engine runs inside your browser, so much of the day-to-day calculation happens entirely on your own device. Sensitive information like your birth date, time, and place can be computed without ever being sent to a server.
Reproducible (same input, same result)
The engine is deterministic — there is no randomness in the calculation. Given the same birth date, time, and place, it produces the same result no matter when or where it runs. We derive a "reproducibility hash" from the ephemeris and model versions in use, so this consistency can be independently verified.
Our transparency promise
Coelo does not hide which ephemeris, calculation models, or data versions we use. The "Live configuration" below shows the actual configuration in use at this very moment.
Most astrology apps don't disclose what happens inside their calculations. We aim to be one of the few astrology engines that can show its work, end to end.
Live configuration (as of this page load)
The table below is what "GET /api/audit" returns — the ephemeris, models, and data versions this engine is actually using right now.
- Ephemeris
- JPL DE440 (1550-2650) / DE441 (範囲外) ハイブリッド — JPL DE ASCII (header.4xx + ascp*.4xx, 自前 Chebyshev 補間)
- Kernel version
- JPL DE440 (1550-2650) / DE441 (範囲外) ハイブリッド
- Conversion impl.
- ERFA port (BSD-3-Clause)（参照: pyerfa / SOFA 準拠, DEC-A）
- IERS dataset
- iers-finals2000A-thru-mjd61557
- ΔT source
- per-calculation（IERS or Espenak-Meeus フォールバック）
- Coordinate frame
- ICRF/J2000 → 見かけ黄道座標 of-date
Each individual chart's "reproducibility hash" is derived from your input (birth date, time, place, etc.) combined with this configuration. Given the same input and the same configuration, the result — and the hash — will be identical no matter where in the world it's computed.
See it for yourself
Create a chart with your own birth date. From the accuracy badge on the results screen, you can always come back to this page.
Create your chartCoelo provides astrology-based information for entertainment and as a reference for self-understanding; it does not guarantee the accuracy of calculation results or interpretations.