Re: Astronomical Data Accuracy

• To: mathgroup at smc.vnet.net
• Subject: [mg112981] Re: Astronomical Data Accuracy
• Date: Sat, 9 Oct 2010 06:34:20 -0400 (EDT)

```Thanksgiving Day Canada   Happy   USA Columbus Day

Following on the email below,
Some years ago, I had been able to analyze a number of solar eclipses,
Up to about 3000 y old,
Using MWR SciAstronomer, historical data, and a number of other programs.
Maximum resulting data spread was about 2 days on a 2000 years old solar eclipse.

I have also been analyzing a number of solar eclipses,
Occurred up to about 15 years in the past, and
Will occur up to about 15 years in the future,
At satellites located in the GeoStationary Orbit.
The resulting data spread is in minutes.

It would be nice to know what exact input parameters have been used in MWR SciAstronomer,
Beyond info provided in the manual,
How to change those parameters, add new objects,
What equations have been used, and how (if possible) to add new terms in those equations?

Thanks, Andy

-----Original Message-----
From: Tim McShane [mailto:tmcshane1 at verizon.net]
Sent: Sunday, October 03, 2010 03:39
To: mathgroup at smc.vnet.net
Subject: [mg112981] [mg112847] Astronomical Data Accuracy

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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