SOFA.jl

SOFA.jl is a pure Julia implementation of the International Astronomical Union's Standards of Fundamental Astronomy (SOFA) library: the authoritative algorithms for fundamental astronomy, covering calendars and timescales, Earth rotation, precession-nutation, astrometric transformations, ephemerides, star catalog conversions, and the supporting vector-matrix toolkit.

No compiled C library is required. Function names mirror their SOFA C counterparts with the iau prefix removed (e.g. cal2jd instead of iauCal2jd), all computed values are returned by the function call (nothing is returned by reference), and the official SOFA C test suite is reproduced in the package tests to prove compliance of the core functionality.

Installation

SOFA.jl is registered in the Julia General registry:

pkg> add SOFA

Quickstart

julia> using SOFA

julia> cal2jd(2026, 7, 22) # Gregorian calendar date to two-part Julian Date
(mjd0 = 2.4000005e6, mjd = 61243)

julia> dat(2026, 7, 22, 0.0) # Δ(AT) = TAI - UTC, in seconds
37.0

julia> utctai(2400000.5, 61243.0) # UTC to TAI, as a two-part Julian Date
(day = 2.4000005e6, fraction = 61243.00042824074)

julia> era00(2400000.5, 61243.0) # Earth rotation angle, in radians
5.225889183066003

julia> icrs2g(1.459672, 0.384225) # ICRS coordinates of the Crab Nebula to galactic, in radians
(lon = 3.2211352911293876, lat = -0.10095691332274818)

The full function reference is organized into topical pages mirroring the structure of the library. Start at the API Reference for an overview.

Package version ⟷ SOFA release correspondence

Package versions correspond to the following releases of the SOFA C library. As of v2.0 the package is a pure Julia implementation; the v1.x series wrapped the compiled SOFA C library and is maintained on the release-1.x branches.

Relationship to other packages

• Astrometry.jl: Where this implementation originated. It was developed by Dr. Paul Barrett as the Astrometry.SOFA submodule before being migrated to this package.
• ERFA.jl: A wrapper of the ERFA C library, the liberally-licensed fork of SOFA C. SOFA.jl provides the same functionality in pure Julia and serves as a drop-in alternative.

License and attribution

This package is derived from, but is not an official product of, the International Astronomical Union SOFA collection, and is not endorsed by the IAU SOFA Board. Its distribution is permitted and compliant with the SOFA license. See the LICENSE for details. Please report any bugs to the package issue tracker, not to the SOFA Board.