# IAU SOFA derived-computation notice

Parts of SiriusX's Earth-rotation, sidereal-time, and precession computations are derived from algorithms and coefficient sets provided by the International Astronomical Union Standards of Fundamental Astronomy (IAU SOFA) software collection. SiriusX is an independent TypeScript implementation and **does not constitute software provided by or endorsed by SOFA**.

The SiriusX implementation differs from the SOFA reference library in important ways: it uses JavaScript numbers and single-Julian-Date convenience APIs, exposes a smaller visual-astronomy surface, and currently omits the full nutation, aberration, polar-motion, relativistic, and observed-place pipelines. SOFA remains the appropriate reference for precision fundamental astronomy.

## SOFA Software License requirements for derived works

1. The Software is owned by the IAU SOFA Board ("SOFA").
2. Permission is granted to anyone to use the SOFA software for any purpose, including commercial applications, free of charge and without payment of royalties, subject to the conditions and restrictions below.
3. Users may copy and distribute SOFA source code and use and adapt its code and algorithms. A derived work must:
   - state that it uses routines and computations derived from SOFA and is not provided by or endorsed by SOFA;
   - describe how it is based upon, contains, or differs from the original SOFA software;
   - not use the prefix `iau` or `sofa`, or trivial modifications of those prefixes, in derived routine names;
   - not misrepresent the origin of SOFA components or claim authorship of the original software;
   - reproduce these requirements intact in source distributions and apply them to downstream modification rights.
4. Users shall not bring SOFA into disrepute through misuse, inappropriate tasks, or inappropriate modification.
5. SOFA is provided “as is”, without warranties of performance, fitness, merchantability, or non-infringement, and SOFA is not liable for consequential, incidental, or special damages.
6. Availability of one SOFA version under these terms does not imply that future versions will use the same terms.

Official terms and attribution guidance are maintained by the IAU SOFA Center at `www.iausofa.org`.