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| Richard B. Langley                            E-mail: lang@unb.ca         |
| Geodetic Research Laboratory                  Web: http://gge.unb.ca      |
| Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142   |
| University of New Brunswick                                               |
| Fredericton, N.B., Canada  E3B 5A3                                        |
|        Fredericton?  Where's that?  See: http://www.fredericton.ca/       |
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________________________________________
From: central_bureau@iers.org 
Sent: February 24, 2021 12:52 PM
To: messages@iers.org
Subject: IERS Message No. 423: New release of the IAU SOFA software library

⚠External message: Use caution.

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IERS Message No. 423                                   February 24, 2021
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New release of the IAU SOFA software library


The 17th Release of the SOFA (Standards of Fundamental Astronomy)
Software Library was made available on 2021 January 25th at 14:00 UTC.
This was a major release which implemented extra defensive precautions
when computing refraction at low altitudes and the application of polar
motion handling was changed to rigorous. Documentation was expanded,
including a new cookbook for the SOFA Vector Matrix Library, and
typographical and other minor corrections were applied. Changes were
also made to the test programs for both distributions.

A minor release (17a) for both the Fortran and ANSI C versions of
Release 17 of the SOFA software library was made on 2021 February 24 at
12:00 UTC. The change relates to the handling of leap seconds during the
period 1960 and 1971. Between the introduction of UTC at the start of
1960 and the first leap second at the end of 1971, there were a series
of small offsets and rate changes with respect to TAI. The SOFA routine
D2DTF takes these into account, but a shortcoming in the algorithm meant
that under certain conditions a leap second could be flagged even though
none had occurred. Such cases are extremely rare, and moreover, depended
to some extent on compiler behaviour, affecting rounding.

See the SOFA website at http://www.iausofa.org for the latest downloads
and details of all changes.

SOFA operates under the auspices of the International Astronomical Union
(IAU) to provide algorithms and software for use in astronomical
computing. The initiative is managed by an international panel, the SOFA
Board, appointed through IAU Division A. The Board obtains the latest
IAU-approved models and theories from the fundamental-astronomy
community, implements them as computer code and checks them for
accuracy. SOFA works closely with all the Commissions of the Division
and with the International Earth Rotation and Reference Systems Service
(IERS).


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