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Astronomical Data Accuracy


Tim, I find that AstronomicalData is not much use for celestial 
navigation work. Note that AstronomicalData[] does not list "Aries", or 
anything involving Vernal Equinox, nor does it list any of the 57 
navigational stars. But I have made only very limited trials with it.

Rob

*************
Hi,
Does anyone know what the accuracy is for the AstronomicalData
calculations for "Altitude" for the sun, moon, planets? I'm writing a
Mathematica program to solve celestial navigation problems. I used the
following code:

AstronomicalData["Sun", {"Altitude", {2010, 10, 1, 12, 0, 0}, {39.,
-77.}}, TimeZone -> 0]

This gives a result of 9.83748 deg.

However, when I ran the same computation using The United States Naval
Observatory (USNO) online data service (www.usno.navy.mil/USNO) the
altitude was given as 9.93889 deg. This is a difference of 0.1 deg.
I'm sure the Mathematica AstronomicalData functions were never intended
to replicate the accuracy and precision of the USNO computation.
However, 0.1 deg seems a bit much, especially when doing
navigation/astronomy calculations. Does Mathematica use low accuracy
formulae, or did I do something wrong? Any help would be appreciated.
Thanks,
Tim
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