JPL Moshier Ephemeris

Independent C ephemeris engine using JPL kernels through CALCEPH as the primary backend and independently verified Moshier-derived/public-domain algorithms as secondary components where appropriate.

This library is developed and owned by Jayesh Mepani. It provides an independently implemented JPL/Moshier/VSOP+ELP+Meeus engine and a project-owned API surface.

Goal

• Provide an independent ephemeris engine for astrology, astronomy, and calendrical calculations.
• JPL .bsp kernels through CALCEPH provide the high-precision numerical ephemeris path.
• Add verified analytical/public-domain components only when provenance is clear.
• Keep the primary public API under the project-owned jme_* prefix.
• Preserve lossless I/O contracts: no presentation rounding, no hidden output reshaping, no dropped status values, and no silent downgrade to a different calculation contract.

Current Status

This repository now contains a substantial implemented ephemeris engine, but it is still not exact across every domain.

Current status summary:

• CMake build
• public C header at include/jme/jme.h
• jme_* primary API
• context/path/version API
• Julian day conversion API
• CALCEPH backend boundary
• analytical fallback engines for Moshier, VSOP87, ELP2000, and Meeus
• C-level engine selection for wrapper/config use: ENGINE=JPL, ENGINE=MOSHIER, ENGINE=VSOP_ELP_MEEUS, or JME_ENGINE environment selection
• eclipse, occultation, heliacal, house, and physical-phenomena coverage with remaining validation gaps documented in docs/STATUS_AND_DESIGN.md and docs/VALIDATION_AND_COVERAGE.md

No public calculation function may return approximate production output. A function is either exact for its documented contract or it returns JME_ERR with a clear error message.

Read docs/POLICIES_AND_NOTICES.md, CONTRIBUTING.md, and docs/STATUS_AND_DESIGN.md before adding implementation code.

Build

cmake -S . -B build
cmake --build build
ctest --test-dir build --output-on-failure

With Visual Studio generators:

ctest --test-dir build -C Debug --output-on-failure

If CALCEPH is installed and discoverable, the library builds with CALCEPH support. Without CALCEPH, the API still builds and returns explicit backend errors for ephemeris calculations.

Backend Data

Supported JPL kernel choices include de440s.bsp, de440.bsp, and de441.bsp.

Kernel files are not vendored in this repository. Download release-packaged kernels from:

https://github.com/jayeshmepani/jpl-ephemeris/releases/tag/jpl-kernels

de441.bsp is larger than GitHub's single release-asset limit, so the release publishes it as split parts with checksums.

jme_set_jpl_file("path/to/de440s.bsp");

Engine Selection

Wrappers should not reimplement backend selection. Configure the C library directly:

jme_set_astro_models("ENGINE=JPL", 0);             /* strict JPL/CALCEPH, no analytical fallback */
jme_set_astro_models("ENGINE=MOSHIER", 0);         /* Moshier-first analytical planets */
jme_set_astro_models("ENGINE=VSOP_ELP_MEEUS", 0);  /* VSOP87 + ELP2000 + Meeus analytical stack */
jme_set_astro_models("ENGINE=AUTO", 0);            /* JPL first, then analytical fallback */

If no explicit engine token is set, the library also reads JME_ENGINE=JPL, JME_ENGINE=MOSHIER, JME_ENGINE=VSOP_ELP_MEEUS, or JME_ENGINE=ANALYTICAL.

License

The independent code in this repository is licensed under the MIT License. Third-party backend libraries and data keep their own licenses/notices.