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Re: (meteorobs) Re: Yorktown meteors
I apologize. At the time, I was in my mind answering the question, "Does it
change?". The answer is yes. But I never stopped to estimate how much it
changes and that is about 50 arc seconds per year which is not too significant
in even 200 years or so. So sorry! I am too inclined to stick my neck out when
when I don't really know what I am talking about. However the Software that you
and Robert are referencing should certainly take this couple of degrees into
account. We used to always call this precession, "The precession of the
equinox".
Dave Hostetter wrote:
> >
> > Actually a solar longitude of 208.0 back in 1781 would have occurred at
> > 23:22 UT on October 16. This would have been on the evening of October
> > 16, 1781 in eastern USA.
> >
> > Bob Lunsford
>
> Hi, Bob:
>
> That's interesting. The Astronomy Calculator at
> http://www.halcyon.com/gml/astro/ (which generally seems to work pretty
> well) gives a peak almost exactly 24 hours later than you got -- 23:13:31 UT
> on October 17, 1781. I wonder what the discrepancy is.
>
> But the question remains -- is the change in the date of the Orionids' peak
> (from around the 17th in 1781 to around the 21st now) due simply to
> precession as Robert Gardner suggested, or due to precession plus other
> factors? For instance, are there changes in the meteoroids' orbital paths
> over the centuries that would cause the proper solar longitude for the peak
> to be something other than today's value of 208 degrees? I suspect that
> precession is the complete answer, but I'm not sure.
>
> Dave
>
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