Astronomical Data Accuracy

*To*: mathgroup at smc.vnet.net*Subject*: [mg112847] Astronomical Data Accuracy*From*: "Tim McShane" <tmcshane1 at verizon.net>*Date*: Sun, 3 Oct 2010 03:38:44 -0400 (EDT)

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