[tz] Fwd: Bulletin C number 58

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Sat Jul 27 19:53:54 UTC 2019

On 2019-07-27 06:54, Alois Treindl wrote:
> On 27.07.19 05:16, David Patte wrote:
>> For my products I use an algorithm (Meeus; Astronomical Algorithms 1998) to
>> 'predict' deltaT into the future. Does anyone have a good source for a more
>> recent algorithm that takes into account IERS values since 1998?

> In Swiss Ephemeris, we have an implementation of delta T which tries to be state
> of the art.
> See documentation here
> https://www.astro.com/swisseph/swephprg.htm#_Toc11319101
> and source code here
> https://www.astro.com/ftp/swisseph/src/
> The delta T source code is in file swephlib.c
> https://www.astro.com/ftp/swisseph/src/swephlib.c
> The implementation is complicated by the fact that we try to be consistent with
> different versions of JPL ephemerides, which use different values for the Moon's
> tidal acceleration.
> All the code of Swiss Ephemeris is published under GPL.
> A commercial license is available for those who do keep their projects free of
> the obligations arising from Gnu public license,

Many developers who wish to promote using their code as a standard choose
instead to license under the BSD or MIT licences as an option to or instead of
the GPL, any mention of which deters most commercial licensees from even looking.

Commercial licensees would rather deal with a few comprehensive sources than a
bunch of little bits and pieces. As in all forms of commodity publishing, the
issue is not really about buying, it is getting anyone interested in any of a
particular author's works: the publishing businesses take a statistical shotgun
approach, in the hopes that buyers will like a few works by some of their authors.

Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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