108 lines
4.7 KiB
ReStructuredText
108 lines
4.7 KiB
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==============
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Bibliography
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==============
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Further reading on the concepts and technology behind Skyfield.
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*USNO Circular 179*
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by George H. Kaplan, October 2005
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https://www.usno.navy.mil/USNO/astronomical-applications/publications/Circular_179.pdf/at_download/file
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My favorite introduction to how the International Astronomical Union
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responded in 1997 and 2000 to the problems with the old J2000 system
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by adopting the ICRS and a new Earth rotation model. Thanks to
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Kaplan’s explanations, I finally understood the maneuvers of the
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USNO’s freely available `NOVAS library`_ (which comes with a Python
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interface!) when dealing with dates and coordinate systems, and I
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was able to perform the same calculations correctly in Skyfield. It
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also provided a useful introduction to the JPL ephemerides that
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NOVAS uses.
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*User’s Guide to NOVAS Version F3.1,* March 2011
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http://aa.usno.navy.mil/software/novas/novas_f/NOVAS_F3.1_Guide.pdf
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There were also several useful tidbits of information in the United
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States Naval Observatory’s guide to using NOVAS. It tends towards
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more practical and user oriented advice than does the Circular, and
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of course was also my guide to the library’s concepts when I used it
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as my model for Skyfield’s internal astrometry routines.
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*SPICE Required Reading documents*
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https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/kernel.html
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https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/spk.html
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https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/daf.html
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When implementing Skyfield’s sister library `jplephem`_, these
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documents were invaluable for their detailed description of the .bsp
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binary file format as well as the description of how the SPICE
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system combines multiple ephemeris segments to learn the
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displacement between two Solar System objects.
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*JPL Solar System Dynamics directory of ephemeris PDFs*
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ftp://ssd.jpl.nasa.gov/pub/eph/planets/ioms/
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I cannot always find the official documentation describing a
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particular JPL ephemeris, but this directory is always a good
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starting point, as it collects several of the PDFs together in one
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place.
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*Historical values of the Earth's clock error ∆T and the calculation of
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eclipses* by Morrison & Stephenson, 2004
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| http://adsabs.harvard.edu/full/2004JHA....35..327M
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| `Full PDF <http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2004JHA....35..327M&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf>`_
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Detailed discussion of the fact that ∆T has the shape of a parabola
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over history because, omitting short-term variations, the shortening
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length of Earth’s day makes the difference between modern clock time
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and actual sunrise and sunset skew ever longer over the centuries as
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the tiny error introduced each year gradually accumulates. Ancient
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eclipses for which records survive are our one point-source of data
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about how far the error had accumulated each century.
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*Delta T: Past, Present and Future* at the United States Naval Observatory
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http://asa.usno.navy.mil/SecK/DeltaT.html
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A few well-presented plots of ∆T and its behavior over the past few
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centuries. I tended to have this page always open in another tab
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while reading about ∆T on other sites, so that I could correlate the
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descriptions of each text against the visuals here.
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*IERS Rapid Service/Prediction Center*
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links at the United States Naval Observatory
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http://maia.usno.navy.mil/
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The many links on this page helped me sort out the various raw
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sources of Earth orientation data that are available, and decide on
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the ones that needed to be built into Skyfield. I also made many
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visits to the IERS web site itself:
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http://www.iers.org/IERS/EN/DataProducts/EarthOrientationData/eop.html
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but found the USNO site to always be the better starting point.
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*The ∆T pages at the NASA Eclipse Web Site*
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| http://eclipse.gsfc.nasa.gov/SEhelp/deltatpoly2004.html
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While most of the pages about ∆T at the Eclipse Web Site are a basic
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introduction to the concept, the “Polynomial Expressions” page
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provides something new: the polynomials that Espenak and Meeus used
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as their fit to ∆T when building their *Five Millennium Canon of
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Solar Eclipses: −1999 to +3000.*
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When the day comes that I implement eclipse logic in Skyfield, I
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will be interested in comparing my results against the `Espenak and
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Meeus paper itself`_!
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.. _NOVAS library: http://aa.usno.navy.mil/software/novas/novas_py/novaspy_intro.php
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.. _Espenak and Meeus paper itself: http://eclipse.gsfc.nasa.gov/5MCSE/5MCSE-Text11.pdf
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.. _jplephem: https://pypi.python.org/pypi/jplephem
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