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arXiv · 2610.38410

PyMsOfa 2.0: A Pure-Python Implementation of the IAU Standards of Fundamental Astronomy Service

Dongjie Tan·Jianghui Ji·Jiacheng Liu
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Abstract

Astrometric calculations require authoritative algorithms so that every result is correct and reproducible. The Standards of Fundamental Astronomy (SOFA) service of the International Astronomical Union (IAU) provides such algorithms, officially released only in Fortran 77 and ANSI C. In an earlier paper we presented the first version of PyMsOfa, a Python package wrapping the SOFA C library. Here we present PyMsOfa 2.0, which re-implements the complete SOFA library in pure Python with NumPy. All 247 official SOFA routines are ported directly to Python, requiring no compilation of any external C library and running identically on Linux, Windows, and macOS. The routines operate on NumPy arrays, so arguments can be processed in batch, which is convenient for survey pipelines and Monte Carlo simulations. The package also provides an extension module with validated models not yet part of the official SOFA release, such as the improved precession--nutation model IAU 2006$_{J_2}$/2000A$_{R26}$. The reimplementation reproduces the official SOFA algorithms: all constants, series, and coefficients are taken unchanged from the SOFA source files, and routine names differ only by the pym prefix. We verify every routine against the official SOFA C release: most reproduce the C results to machine precision, the remainder within the accuracy tolerance stated in the SOFA documentation. The package has been applied to Gaia astrometric reduction and used in astrometric studies of the Closeby Habitable Exoplanet Survey (CHES) mission, and is available through PyPI, GitHub, and Zenodo.

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Dongjie Tan, Jianghui Ji, Jiacheng Liu. 2026-10-28. PyMsOfa 2.0: A Pure-Python Implementation of the IAU Standards of Fundamental Astronomy Service. https://arxiv.org/abs/2610.38410

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