P. Clay Sherrod Dec 14, 2012
----- Original Message -----
From: "Bill J. Gray" <pluto@...>
Cc: "barringtonri" <pecorp@...>
Sent: Friday, December 14, 2012 11:05 AM
Subject: Re: [guide-user] Re: Where is C/2012 S1 (ISON) ?
> Hi Pete,
> As I write this, I see that Clay has directed you to the file
> on the MPC site. Be advised: this will work if you aren't using the
> updated Guide that I posted yesterday. That update will simply
> download and use the required files when you use Extras...
> Asteroid/Comet Options... Add MPC Comets/Asteroids... Click to
> download updated comet data and add it to Guide.
> I'd recommend just going with the revised Guide.
>> I am usually very confused with MPC's website and had been accessing their
>> http://www.minorplanetcenter.net/iau/MPCORB/CometEls.txt data from the comet
>> link on their http://www.minorplanetcenter.net/iau/MPCORB.html page.
>> Why would they have two different datasets?
> For various historical reasons (I think), MPC has a whole slew of
> different orbital element formats. There's an MPCORB.DAT format, which
> works only for heliocentric elliptical orbits (i.e., no comets, and a
> serious loss of precision for near-parabolic objects). There's an
> eight-line format that is more human-readable and which can store
> parabolic, hyperbolic, and non-heliocentric orbits. And an 80-column
> orbit used on Daily Orbit Update MPECs. And there's the format used
> in CometEls.txt... that's the one that isn't readable by Guide.
> MPC has also kindly provided elements in the format used by Guide
> and other desktop planetarium programs. At the time, I very much
> appreciated their efforts in this area. Now, though, I wish I'd
> suggested a single format that would cover all reasonable cases, to
> avoid the current situation of bazillions of orbital element formats.
> Though quite likely, a new format would have led to this situation:
> -- Bill
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