This document answers, in one place, the questions a downstream developer or commercial user should be able to settle without reading source history: what Moira is licensed under, whether its implementation is independent, and how to read its earlier releases.
Moira is released under the MIT License, and will remain so. MIT permits commercial use, modification, and distribution — including building closed-source or paid products on top of Moira — with no copyleft and no AGPL obligations.
Moira was built deliberately as an independent, AGPL-free foundation, so that commercial builders can use it without the licensing entanglements that accompany Swiss Ephemeris–based stacks. That is the point of the project: a clean, permissively licensed engine you can ship commercially without contamination concerns.
Moira’s astronomical and house-calculation code is independently derived from primary sources — spherical trigonometry, the defining geometric construction of each house system, and primary astronomical references (JPL DE441, IAU 2000A/2006) — and is validated against primary authorities (JPL Horizons, SOFA/ERFA, IERS). It does not incorporate Swiss Ephemeris source code.
A per-system account of the derivation basis, and of where Moira’s discretionary choices diverge from convention, is published in HOUSE_SYSTEM_DIVERGENCE.md.
Note on resemblance: house geometry is mathematically forced — there is one correct way to trisect a semi-arc — so Moira’s cusp values converge with any correct engine, including Swiss Ephemeris, at admissible latitudes. That convergence follows from shared mathematics and is not evidence of derivation.
Earlier in Moira’s release history, during a licensing discussion with the Swiss Ephemeris authors, the house module carried — as a conservative precaution — an attribution notice referencing swehouse.c, and written permission was obtained from the authors. Moira’s house implementation is independently derived from the mathematical definitions; the precautionary attribution was therefore determined to be unnecessary and was removed.
Version timeline:
| Releases | swehouse.c attribution notice |
Status |
|---|---|---|
| 2.1.2 – 3.2.3 | Present (precautionary) | Available; retained for reproducibility |
| 3.2.4 and later | Removed | Independently derived; recommended for new work |
Earlier releases are intentionally left available rather than withdrawn, so that any pinned dependency continues to resolve. All releases are MIT-licensed.
This document is the authoritative, standard-path record of Moira’s license and provenance. It is intended to be discoverable without recourse to commit history.