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Updated obsolete comments about how Delta-T is calculated.

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Astronomy Engine used to use USNO historical and predictive tables,
along with linear interpolation, to calculate Delta-T values.
The problem with the USNO tables is, they did not work well outside
a few centuries around present day.

Later I replaced with Espenak & Meeus piecewise polynomials
that work over a much larger time span (thousands of years).
I just discovered there were still comments in the code referring
to the USNO models. I updated the ones I could find to reflect
the current truth about how the code works today.
This commit is contained in:
Don Cross
2021-03-27 19:44:37 -04:00
parent 6f98095cae
commit 5cd0e60d74
19 changed files with 5295 additions and 5288 deletions
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6
source/python/README.md
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@@ -521,9 +521,9 @@ Sometimes we need to adjust a given [`Time`](#Time) value by a certain amount of
This function adds the given real number of days in `days` to the date and time
in the calling object.
More precisely, the result's Universal Time field `ut` is exactly adjusted by `days`
and the Terrestrial Time field `tt` is adjusted correctly for the resulting UTC date and time,
according to the historical and predictive Delta-T model provided by the
[United States Naval Observatory](http://maia.usno.navy.mil/ser7/).
and the Terrestrial Time field `tt` is adjusted for the resulting UTC date and time,
using a best-fit piecewise polynomial model devised by
[Espenak and Meeus](https://eclipse.gsfc.nasa.gov/SEhelp/deltatpoly2004.html).
The value of the calling object is not modified. This function creates a brand new
[`Time`](#Time) object and returns it.

6
source/python/astronomy.py
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@@ -547,9 +547,9 @@ class Time:
in the calling object.
More precisely, the result's Universal Time field `ut` is exactly adjusted by `days`
and the Terrestrial Time field `tt` is adjusted correctly for the resulting UTC date and time,
according to the historical and predictive Delta-T model provided by the
[United States Naval Observatory](http://maia.usno.navy.mil/ser7/).
and the Terrestrial Time field `tt` is adjusted for the resulting UTC date and time,
using a best-fit piecewise polynomial model devised by
[Espenak and Meeus](https://eclipse.gsfc.nasa.gov/SEhelp/deltatpoly2004.html).
The value of the calling object is not modified. This function creates a brand new
#Time object and returns it.