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Constants used in equation_of_the_equinoxes_complimentary_terms()

See original GitHub issue

In the calculation of equation_of_the_equinoxes_complimentary_terms()

https://github.com/skyfielders/python-skyfield/blob/eda5feac325d5feeca395e904a7f8cf6adbc6ec6/skyfield/nutationlib.py#L111

some of the values used seem to vary from other published sources. The value 715923.2178 appears in the code, but it appears as 1717915923.2178 in SOFA and in other places eg. http://www.iausofa.org/2010_1201_C/sofa/fal03.c

There are similar variances in the calculation of the other fa values. Assuming this is intended, should there be code comments added to explain the source of the values and the discrepancies?

Issue Analytics

State:
Created 3 years ago
Comments:10 (10 by maintainers)

Top GitHub Comments

1reaction

glangfordcommented, Sep 14, 2020

No, I haven’t actually run the two and compared behaviors - I was just trying to understand where the magic numbers came from, and saw that the two implementations used many of the same constants but not identical ones.

1reaction

brandon-rhodescommented, Sep 14, 2020

Oh, and: the NOVAS guide has an Appendix D that compares SOFA and NOVAS.

https://github.com/brandon-rhodes/python-novas/blob/a40c662493da86da51e9b09361b5415a4fbbbf9e/Cdist/NOVAS_C3.1_Guide.pdf

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