[guide-user] Of many things...

Bill J. Gray Feb 7, 2000

Hi folks,

First, a warning: I've been out sick for two days, and downloaded
a dauntingly long stack of e-mails this morning. It'll be a while before
I get everything answered.

Priority #1 for me, right now, is figuring out and fixing the
'current time' problem. I _may_ have tracked it down to a bug in LUNAR.DLL.
If I'm right about this, the problem should involve _any_ change in the time
at all... not only would setting the 'current time' do it, but setting the
time ahead an hour, and so on, ought to make trouble.

To verify that I've fixed the right thing, I'd appreciate it if folks
would download this file:

http://www.projectpluto.com/lunar2.zip

(this is about 67 KBytes), see if this revised DLL makes the problem
go away, and let me know your results.

The worrisome part of this is that, to make the 'fix', I didn't have
to change the code at all. All I had to do was to recompile certain parts
of LUNAR.DLL with 'default' code optimization. It looks to me that the
bug was caused by the compiler. But compiler bugs are _very_ rare, almost
impossible to prove, and are usually the excuse of lazy programmers.

This _may_ be related to the long-standing problems with the AMD-K6
described at

http://www.projectpluto.com/update7b.htm#amd

I have hopes that fixing one bug will fix both. (A sign, perhaps, of
my truly cheerful and optimistic nature.)

SCOPE CONTROL:

Mel, your thought about sending a full ephemeris followed by an
'execute' command makes sense to me. I'd be happy to have that go to either
a file or through a COM port... though those looking for the file might do
well to just use the 'make ephemeris' option, enabling them to produce
whichever data is desired (RA/dec, and/or alt/az).

One minor problem with all of these 'extended commands' is that
people might try them with 'real' LX-200s that don't support them. So I'd
like to have the first command, such as ':SL#', return an acknowledgment,
so Guide can proceed safe in the knowledge that it's really talking to
your hardware.

I've been holding off on these revisions until this 'current time' bug
is fixed. With any luck, that problem is about to vanish.

Berthold, about your proposed alignment star selection... I'm not sure
I follow your meaning. Generally, for error correction, you want stars
scattered over the sky, not necessarily sharing an alt or azimuth with an
existing alignment star. Why would you want to get the sort of list you're
asking for?

LEDA/GALAXY DATABASES:

Owen, at one time, I did indeed use the PGC-1996. Just before Guide
7 came out, I got an updated version (a sort of 'PGC-1998') that bumped
the number of galaxies up from 106,000 (roughly) to about 169,000, and
fixed some of the more blatant errors in PGC-1996.

I dunno if the fixing up of errors makes it quite as good as NED
(though the example Brian Skiff mentions, NGC 4486A = MCG +02-32-110,
_is_ handled correctly in PGC-1998, and certain other prominent errors
in PGC-1996 were fixed in PGC-1998.)

A carefully done merger of galaxy catalogues, of the sort Brian Skiff
suggests, would indeed be helpful... if nothing else, it can let you
flag situations where catalog A doesn't match catalog B, whereupon a
human can look at the result and make a decision. It sounds like a great
research project to me. If anyone undertakes it, I'd be very happy to
see the results.

AMALTHEA (AND OTHER INNER SATELLITES):

Derek Wong asked: "...I don't understand why a near circular orbit
is more difficult [than the distant gas-giant satellites]." Given
suitable data, it shouldn't be. The _Explanatory Supplement to the
Astronomical Almanac_ does give circular elements for Amalthea (and
elliptical elements for Thebe, another inner satellite of Jupiter).
Unfortunately, the Amalthea orbit dates back to 1950, and probably
bears little resemblance to the current orbit. (I've already learned
that the difference between the _Explanatory Supplement_ orbit for
Phoebe and the real one is depressingly great.)

However, I've found data that ought to let Guide show _all_ the assorted
inner moons of gas giants. So this is indeed a possibility.

"...Jeff Medkeff says he has seen [Amalthea] in a 14" scope." I'm
impressed! Barnard discovered it in a 36" refractor.

Regarding cometary globules: this might be good as a user-added dataset.
The main obstacle is finding a good dataset listing these objects. I'm open
to suggestions.

PALOMAR 4:

Denis, I'm afraid that fixing this one is nearly impossible. The data
is in a strange binary format, in VARIABLE.LMP (which actually contains
display data for variables and deep-sky objects.)

Just around the time Guide 7 was released, I was playing around with
a new dataset of globular clusters... one which fixes this problem (and,
I think, some others.) Copy the file

\clusters\globs_97.tdf

from the CD-ROM over to your Guide directory, and turn on the "Globular
clusters (Harris 1997)" user-added dataset. You'll note, first, that
Palomar 4 now appears correctly.

For the 'go to... Globular' function, though, the data comes from
GLOBULAR.NAM. Edit that file, look for Pal 4, and bump it north by
exactly three degrees, and you should be in business.

As you might expect, I intend to use this new dataset (or a similar one)
for globulars in Guide 8.

GUIDE ON A HARD DRIVE:

Karen, I'm afraid you've been misled by sloppy programming. The
"please insert Guide CD" message is vestigial; just click "OK" and
ignore it. This part of Guide is not bright enough to realize that the
Guide CD already _is_ available, and that asking to have the CD inserted
is unnecessary.

-- Bill