[vsnet-chat 297] Re: Electronic GCVS

[Stan Walker <astroman@voyager.co.nz>]

At 02:34 AM 5/4/97 GMT, Charles Scovil wrote:
>A lot has been said about the availability of the GCVS in electronic form, and
>how very big it is and what a problem it is to handle the large file.  Why do
>your own programming or conversion when it has already been done by at least
>two commercially available programs.  One is "The Sky" from software Bisque
>(quite expensive), the other, and my favorite, is called "The Guide".  It is
>put our by Project Pluto.  Both are advertised is Sky & Telescope and other
>magazines.  "The Guide" is only 69$ US.  It has the entire Guide Star Catalog,
>SAO Catalog, NGC & IC and many others, and the GCVS with all updates. 

I think that there is a misunderstanding here - the GCVS is not difficult to
use in Excel - it just comprises two volumes. Excel and Word are meant to be
used as a package to overcome some of the limitations in either programme.
So there is really no difficulty in handling large volumes of material. 

My other comments in a different context related to what would happen when
the number of entries became 5 or 10 times larger than at present.

I have used Guide 3.0 for several years. It is not a catalogue and does not
substitute for one. It provides some information about variables - but not
the epoch and period which I use a lot. You cannot use it like a catalogue -
say to print out all the Miras between -20 and -40 that are brighter than V
= 7 at maximum. Excel is ideal for this.

Guide does have some other limitations. Its magnitudes seem to be based on
the SAO catalogue so are not visual in many cases. The faint star magnitudes
are also well out in some cases. Thus you get a chart where the stars are in
the correct places, but often the appearance is wrong. Try plotting the
field of VW Hydri where a blue/red close pair appears reversed due to the
colour peculiarities of the source catalogue. Or another field where Antares
comes out at v = 3.3! I still use it a lot but it needs some care. Where
possible I photocopy from the old Czechoslovak Atlas Eclipticalis which
gives approximately visual magnitudes down to 12.5 and actually looks like
the sky through the eypiece. Borealis and Ecliptical don't go as faint. But
Sky Publishing seem to have taken these out of print. 

Some of our people have versions 4 and 5 of Guide but state that there are
still problems. They've made suggestions which seem to have been ignored.

I was also puzzled by some of the categories of variables which seem to
differ from the GCVS. Perhaps these are more recent (sub)classifications but
without any background they tend to be confusing.

I have the feeling that most of these computer charts are aimed at the
armchair market. If you were to make them perfect for variable star
observers they'd lose their main market. And, in any case, there are enough
charts of variables around that it's not a loss. I wouldn't have had a hope
of finding V803 Centauri from Guide but I did find it from a dedicated chart.

The CCD chart information which comes over VSNet at intervals is far more
detailed and very useful - although some southern objects would be great.
I've drawn quite a few charts from these and find them very reliable.

Regards,
Stan Walker

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