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  • From: James Read <J.Read-2 AT sms.ed.ac.uk>
  • To: Rolf Furuli <furuli AT online.no>
  • Cc: b-hebrew AT lists.ibiblio.org
  • Subject: Re: [b-hebrew] Chronology - was uncancellable meaning in hebrew verbs
  • Date: Sat, 04 Jul 2009 17:00:30 +0100

Hi Rolf,

this is a quick and impulsive first reaction response from my experience as a computer scientist.

I wouldn't pay too much attention to the similarity of the results in the programs. They are probably all using the same underlying algorithm and only really differ in the front end. So, the assumption is that the algorithm is correct.

Concerning errors, there are a number of potential sources. One source of error is whether the algorithm is correct. A good example of this is the evolution of our understanding of the length of a solar year. As our understanding has increased our algorithm has become more accurate.

The second, and perhaps most important, source of error for you consideration is the fact that computer simulation make frequent use of floating point numbers. The implementation of floating point numbers means that, unlike integers, they are approximations of values. The implication of this is that the more sums we make using floating point numbers the greater our incurred error due to rounding errors. A good program should calculate the boundaries of the error and make them known to you.

A third source of error the principle of GIGO (garbage in garbage out). Such a program needs an accurate starting point to work back from. Minimal differences in the actual present state of the universe could have significant impacts on the output of the program. An example that is often quoted is the butterfly effect. Even the best climate change simulations on the largest super computers on earth make significant mistakes because we do not know the exact present state of the earth to feed into the algorithm (and even if we did know it, it would take too much data to input let alone process). I'm not saying your astronomical simulations will be way off because of this. I'm just making you aware of the issues.

Anyway, thanks for you answer. If I get time I'll look into the programs you mention.

James Christian

Quoting Rolf Furuli <furuli AT online.no>:


Dear James,

While I have a very good background in Hebrew and Akkadian (having
taught both languages for 12 years), I have little background in
mathematics and astronomy. So here I have to rely on others. I use
four astro-programs: TheSky6., SkyMap Lite, CyberSky 4, and TheSky X
(for Macintosh). As for solar and lunar eclipses, all the programs
give the same information, and this is the same as can be found at
NASA.

Some of the positions of the moon and the planets found in old
cuneiform tablets (some being real observations, an quite a lot being
backward calculations) have very specific measures; some go down to
the equivalent to 1/2 degree, and others even to a few minutes. In
these specific cases there can be some problems because the programs
sometimes differ, in special cases up to 2 degrees. I have discussed
the reason for this with several US astronomers, and they have told
me that the differences probably are caused by slightly different
mathematical formulas in the different programs. Their advice has
been to use TheSky X or the related TheSky6, because these are the
most accurate programs. I have a colleague at the University of Oslo,
who is professor in astrophysics with archaeoastronomy as one of his
special fields. He has at my request made some calculations-not using
any of the mentioned programs-and his results are almost exactly the
same as those found by the help of TheSky X. I therefore think that
the positions I have found has a good foundation.


Best regards,

Rolf Furuli
University of Oslo


Sounds like good stuff. That's the kind of thing I've been meaning
to look into for a long while.

What sources do you use for astronomical events such solar eclipses etc?

James Christian



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