----- Original Message ----
> From: johnhkmurrell <[email protected]>
>
> --- In [email protected], Patrick Chevalley
> wrote:
> >
> > Normally a new element set you download do not replace the previous
> one for the same object but add the elements for the new date.
> >
> > This allow you to have in the database the element for a periodic
> comet at different opposition, the program use the right element
> depending on the date.
> > The same is done for the asteroids.
> >
> > In your case there is probably a problem with the comet
> identification from one of the element set and the program think it is
> a different object.
> > The identifier for this comet is CK07N030.
> >
> > > 14h41m02.06s -14°53'19.5" Cm C/2007 N3 (Lulin) 2009-02-08
> 05h00m00s m: 6.9
> > >phase: 49 ° dist: 0.7155au rsol: 1.2882au tl:0.05au ref:1/2007-10-27
> > > 14h41m15.68s -14°54'15.0" Cm C/2007 N3 (Lulin) 2009-02-08
> 05h00m00s m: 6.9
> > >phase: 49 ° dist: 0.7206au rsol: 1.2910au tl:0.04au ref:2/2008-11-30
> >
> > We see that one element is from October 2007 and the other from
> February 2009.
> >
> > Can you look at your directory cartes_du_ciel\MPC if you still have
> the COMET.DAT file from October 2007 and search the identifier for
> Lulin in column one.
> >
> > Patrick
> >
> Hello Patrick,
>
> Is the last field the date the file is supposed to be ? i.e the one
> starting 'ref:'
That's probably the epoch of the elements. That's what Patrick was referring
to. Orbits "drift" over time due to the effect of gravity from Jupiter and
other factors, so elements are occasionally recalculated. For the most
accurate prediction, you want to use elements where the epoch is close to the
time of prediction.
> I have a file from the 2007-10-27 but none from 2008-11-30 in my
> backup 2 weeks previous to the install of the latest release of V3.
> However I note that if I download the current elements they object
> list has a 'ref:2/2008-11-30'.
> Not sure where you got the February
> 2009 date from.
I think he read the wrong line. The date/time:
2009-02-08 05h00m00s
occurs in both sets, so that's probably the time of the chart.
-John
> I have had a look at the 2007-10-27 file and the comet identifier
> seems correct.
>
> Deleting the old data cured it but it would be interesting to find the
> cause
>
> John Murrell
>
>
>
>
>
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