Comets and Jupiter event fixes

Bill Gray Jan 2

Hello all,

Short version : I am reasonably sure that if you download this file :

(about 1.2 MBytes) and unZIP it in your Guide folder, comets will
work correctly and you'll have Jupiter events extended to 2070. If
you do not, please let me know. Once I get some confirmations that
I've not broken things, I'll make it the "official" version people
see when they visit the update page.

Longer version, first about the comets, then the Jupiter events.

I am indebted to Rolf Stadelmeier for pointing out that removing
'cometg.dat' fixed the problem. That was the clue I needed to figure
out what needed to be fixed.

'cometg.dat' is a large list of "historical" comet elements; it's
what Guide uses if you ask it where the Great Comet of 1812 was, or
where Halley's Comet was in 1066.

It also contains some predicted returns, including one for P/46
Wirtanen that is looking increasingly dated. Guide has IMCCE data
for comets from about 1995 to the present, plus MPC data for the
_really_ current comets IMCCE hasn't gotten around to analyzing yet.
So there's no real reason to use 'cometg.dat' for comets in the last
twenty years or so.

In the updated version, 'cometg.dat' is simply ignored for any
time after 2000 Jan 1. The overlap is nearly seamless, and you can
still investigate "ancient" comets.

Also, in the updated version, IMCCE data is gathered from its
new location in its new format, at VizieR. I highly recommend that
you go into Extras... Asteroid/Comet Options, click on Add MPC
Comets/Asteroids, and "click to download updated comet data and
add it to Guide".

OK, so about the Jupiter events :

I first wrote the code to compute Jupiter events as a considerably
younger and more foolish programmer, sometime around 1995. At that
point, computing Jovian events was a slow task, so I pre-computed
a list of events covering roughly 1970 to 2020. If I hadn't done that,
you'd have had to wait a while to get a month's worth of events. And
at that point, 2020 seemed unimaginably distant.

The entire list of events was packed into a binary file of about
500 KBytes. My recollection is that computing the events was an
overnight task on a '486 with no math chip. But, of course, when
you asked Guide for a list of Jovian satellite events, the response
was instantaneous.

Fortunately, I still have the code to generate the file, and it
ran without problems. This time, generating an additional fifty years
of events took about five seconds, resulting in another file of about
500 KBytes. The result is included in the above file; you
can now get lists of Jupiter events from about 1970 to 2070.

-- Bill