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Re: 1901 May, 22 Lunar example by French Navy Captain Arago
From: Paul Hirose
Date: 2010 Feb 03, 10:29 -0800
From: Paul Hirose
Date: 2010 Feb 03, 10:29 -0800
I wrote: > Delta T was *negative* in 1901. That unusual circumstance revealed a bug > in my program, which in turn was due to a bug in my positional astronomy > DLL. It's in a feature which isn't used much, and fortunately there's an > easy workaround. I'll update the Web site with a description of the > workaround, and issue a fix soon. Correction: the bug was in the lunar distance program itself. There was nothing wrong with SofaJpl, the positional astronomy "engine" that helps with the computations. It has a function to convert time (duration, not epoch) to angle. The result is put into the interval [0, 2π) radians, so it's never negative, even if the angle is. This behavior is precisely documented. I simply forgot and used the function improperly. The code at my site has been corrected. In addition, the observation data for the Arago lunar distance and occultation have been added to the existing examples in the source code. http://home.earthlink.net/~s543t-24dst/sofajplNet/LunarDist2.html (In the Lunar2.vb file.) --