Re: [guide-user] Comets.dat file

Bill J Gray Feb 16, 2012

Hi Ben,

Ben Hudgens wrote:
> Err, you can disregard my previous inquiry about comets.dat....
> Found an explanation message from several months ago.

Just to recap for the curious: there is no general file of
elements for all comets, the way there is for asteroids. Guide
has to take the "currently observable comets" elements from
MPC and merge them in with previous data.

This is quite imperfect, on many counts. If you skip comet
updates for a few months, a comet or two may come and go without
Guide ever being aware of it. The bizarre comet designation
scheme means that comets can appear twice, once under their
original designation and again under their permanent designation;
Guide can't tell that they're both really the same object. The
MPC list omits all but the biggest and brightest SOHO comets.

I've ideas for getting around this, which will involve using
Patrick Rocher's orbital elements from IMCCE (formerly the
Bureau des Longitudes) :

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

Doing so could fix most of these issues, except for the SOHO
comets... but there's one drawback: the above list is not updated
as frequently as the MPC one. So I may have to take Patrick's
list and patch in holes using the MPC data. Plus additional
patching-in of "ancient" comets and further patching-in of SOHO
ones, probably using JPL's data... the life of a programmer of
astronomy software is rarely an easy one!

-- Bill
>
> ----- Original Message -----
> From: Ben Hudgens
> To: guide-user@yahoogroups.com
> Sent: Wednesday, February 15, 2012 5:31 PM
> Subject: [guide-user] Comets.dat file
>
>
>
> Using Guide 9.0 I d/l comet updates through "Extras", Comets/Asteroids Options.. Add MPC Comets/Asteroids button. Why is this new file showing so few comets (currently only 214) and from where does this file get downloaded?
>
> If I d/l the comet update file from Bill's link at http://www.projectpluto.com/comets.dat , that file currently shows 959 comets, including the latest new comet from a few days ago.
>
> Ben
>