|
 |
"waggy" <hon### [at] handbasket org> wrote:
> So, does anyone have any idea how accurate the sunpos macro is for historic
> or prehistoric dates? I am specifically interested in how much error to
> expect in the sun's position during the first thirty minutes after sunrise
> on the morning of the Winter Solstice, say during year -3000 at the
>
> Also, is there a handy way to determine on which day the solstice occurred
> during that year?
>
> I'm hoping to be able to illustrate, with a nice POV-Ray animation, the
> exceptional service life of Newgrange during a presentation for my civil
> engineering practice course.
>
> Thanks in advance for your help,
> -David Wagner
As far as I can tell, sunpos.inc doesn't correct for precession, which means
it's useless for calculations that far in the past. The link contained in
sunpos.inc is dead, but I found http://www.stjarnhimlen.se/comp/ppcomp.html
that seems to have identical formulas. On that site, point 8 explains how to
correct for precession, although that looks a little too easy to me, as
precession is supposed to be vastly complicated.
There are C programs (with source, so that you can include them in POV!)
here:
http://www.moshier.net/
aa-56 should be what you are looking for. It's supposed to go back
accurately to 3000 BC, but of course 'real' accuracy is unknown.
For finding the solstice that year, I'm sure there's an easy way, but I
can't think of any apart from brute force.
Post a reply to this message
|
|
