Hi Jim,

The designation scheme for comets has caused endless headaches over the
years. I've fixed the 'P/2010 J5' vs. 'C/2010 J5' problem, after I realized
that the leading letter gets changed from time to time (and can be disregarded
safely; you'll never have two comets that differ only in the 'P' vs. 'C'.)

So with the current version of Guide, you at least won't run into that
problem... but any duplicates that you've already downloaded will still be
there. To get around this, I'd recommend replacing your comet.dat file with:

http://www.projectpluto.com/comets.dat

(about 148 KBytes), which is a current, "cleaned-up" source.

It also "cleans up" another source of trouble: situations where a comet
gets a permanent number. For example, when the comet P/2006 U1 was linked
to P/2011 A4, it received the permanent designation 249P.

There are similar problems with asteroids. But in that case, the MPC
provides a convenient, unified 'mpcorb.dat' file; you just replace your
entire asteroid dataset, rather than attempting to merge an old one with
updates. There is no similar unified comet database (*), so I have to do
a bit of hand-editing so that Guide will know which objects are duplicates.

Anyway... with the above 'comets.dat' file, existing blunders are fixed,
and with the current version of Guide, future ones will be limited to cases
where comets get permanent numbers.

-- Bill

(*) There is a somewhat promising solution at

http://www.imcce.fr/fr/ephemerides/donnees/comets/ASCII/ELTDAT.TXT

It's possible that Guide will, at some point in the future, switch to this
as its default source of comet elements. It also includes non-gravitational
parameters and both "total" and "nuclear" magnitude parameters, so it's very
tempting indeed. The only issue with it is that updates are somewhat irregular.