Hi Danny,
thanks for your eloquent reply. For some reason I didn't get it till
today (10/30). Sorry if I appeared impolite by not answering!
I have since added 3 catalogs to my arsenal:
- USNO-A
- UCAC2 (my own version with identifiers)
- WinOccult's catalog, converted by me for use with CdC
Sorry for not explaining my use for these catalogs very well. I'm not
particularly ambitious right now. I just want to be able to identify
each star in my eyepiece. Tycho-2 simply didn't go deep enough for that.
I sometimes participate in asteroid occultation measurements and the
stars they refer to didn't always occur in the catalogs I had. This was
one of the reasons to convert the winoccult catalog.
Thanks,
Sander
PS descriptions on how to create the two catalogs are on my website
http://www.tungstentech.com
Danny Wilson wrote:
>
> Sander,
> You ask a very good question.
> I've closely read Bill Gray's summary about the GSC-ACT at
> [ http://www.projectpluto.com/gsc_act.htm
> <http://www.projectpluto.com/gsc_act.htm> ]. The answer to your
> question depends on what you want to use the GSC-ACT for? Reading the
> thread of your post tonight hasn't offered me any insight about
> that? My primary use for CDC is making charts for AAVSO visual
> variable star estimates.
>
> Since around 1994-95 the AAVSO has used GSC astrometric positions to
> create a star field (print black star dots on a sheet of paper)for
> their charts. Although the GSC is considered to be inadequate for
> photometric magitude data and the AAVSO mostly uses it only on
> preliminary charts for a nova or supernova and GSC magitude estimates
> can be later revised using adequate photometery.
>
> Sander from reading your post you find the Tycho-2 Catalog to be
> indequate in astrometry and you'd like to see as many stars on your
> screen has your C11 telescope shows.
>
> You have only 2 options for a "CDC cat folder ready" catalogue and
> thats the quote, "obsolete" GSC-ACT 1.14GB. or the "dense" USNO A2.0
> which is exactly 6,315,439,692 bytes and +500,000,000 stars and 11
> CDs of star catalog. (I don't feel the current state of art USNO-
> B1.0 which is 80GB with 100 CDs of stars catalog is an option for
> most CDC users.)
>
> Let me quote a tiny portion of Bill Gray's "GSC-ACT files and
> information" URL:
>
> "The purpose of the GSC-ACT project is to recalibrate the Hubble
> Guide Star Catalog (GSC), version 1.1, using the ACT (Astrographic
> Catalog/Tycho) data from the US Naval Observatory." . . . "I expect
> the main use of GSC-ACT will be in asteroid astrometry. And for this
> purpose, the answer to the question of "How much of an improvement is
> GSC-ACT over GSC 1.x?" is: "It cuts down errors a lot." . . . "What
> about photometry?" . . . "First, there is a lack of suitable data.
> The Tycho dataset provides excellent photometry for stars down to
> about magnitude 11, and it is true that this could be used to
> recalibrate bright stars. But it would not necessarily help much at
> fainter magnitudes (i.e., for about 90% of GSC.) (But this objection
> may vanish. It does appear that Brian Skiff's LONEOS.PHOT photometric
> database could extend the range of "decent" photometry quite
> nicely.) . . . Second, it's not clear that the photometry could be
> improved very much. The raw magnitude data coming in from GSC 1.1 is
> sufficiently "random" that recalibration might not result in much of
> a benefit. And thirdly, Dave Monet has recalibrated the A1.0 dataset
> (both photometrically and astrometrically), using ACT. This resulted
> in a much better photometric dataset than GSC-ACT could hope to be.
>
> Sander, is that as clear as "MUD"?
> Personally, I feel Bill Gray knows what he is talking about on the
> topic of star catalogues. This is because any optical telescope has a
> certain degree of image field curvature and when the image forms on a
> flat CCD chip or photographic plate it distorts a tiny bit. When all
> the image data of a whole sky survey is combined to create a star
> catalog all those many optically distortioned plates joined together
> creates two kinds of "errors". First - the stars in the center of
> the field are in better focus the those towards the edge, this makes
> errors in star magitudes (photometric errors). Second - the
> positions of the stars in the center of the field are more accurate
> that those towards the edge this makes star positions distorted
> (astrometric errors). Brian Skiff's LONEOS.PHOT photometric database
> seems to be some sort of "software voo-doo" to focus those somewhat
> out of focus stars at the edge of a CCD or photo plate and reduce
> magitude errors.
>
> To offer a reply to your question:
> I would recommend the GSC-ACT for 2 reasons. First- I think you'll
> learn to deal with an astrometric error of .3 arcseconds (.3") on a
> computer screen, just set the CDC (HST GSC original fits) field at
> min 0 & max 1. Second-The magitude errors (for example: Star
> GSC4766. 1330 - Magnitude: 14.39+/-0.40).
> This star's magitude could be as bright as 13.99 or as faint as 14.79
> and I kinda doubt something like that is going to give you or very
> many amateur astronomers any heartburn!
>
> Best Wishes,
> Danny
>
> Mudcreek Observarory
> Parker County Texas
> Latitude: +32 deg 34 min 11 sec - north
> Longitude : -97 deg 46 min 43 sec - west
>
> =====================================================================
> --- In [email protected]
> <mailto:skychart-discussion%40yahoogroups.com>, Sander Pool <[EMAIL
> PROTECTED]>
> wrote:
> >
> >
> > Yes, I saw that catalog but it doesn't appear to be available for
> > download anywhere. Some sites hold information files and code but
> no
> > data. If you know of a location please let me know.
> >
> > I requested a CD set.
> >
> > Sander
> >
> > starryeyeguy wrote:
> > >
> > > UCAC-2 covers the south pole to about +30 dec from 8th to 16th
> > > magnitude. There is a supplement for the brighter stars derived
> from
> > > Tycho-2. The complete catalog should be available next year.
> > >
> > > Cheers,
> > >
> > > Geoff Chester
> > >
> > > --- In [email protected]
> <mailto:skychart-discussion%40yahoogroups.com>
> > > <mailto:skychart-discussion%40yahoogroups.com>, Sander Pool
> <sander@>
> > > wrote:
> > > >
> > > >
> > > > I'm seeing more stars in my C11 than the Tycho-2 catalog
> contains.
> > > There
> > > > is the GSC-ACT catalog but its homepage on projectpluto says
> it's
> > > > obsolete. USNO is nice but huge and I don't need mag-20 (I
> wish :).
> > > > UCAC-2 sounds promising and contains the range of stars I care
> > > about. If
> > > > I'm reading http://ad.usno.navy.mil/ucac/
> <http://ad.usno.navy.mil/ucac/>
> > > <http://ad.usno.navy.mil/ucac/ <http://ad.usno.navy.mil/ucac/>>
> correctly it's mostly geared
> > > > towards the Southern hemisphere though, right?
> > > >
> > > > So, which catalog do you recommend for dim stars in CdC?
> > > >
> > > > Thanks,
> > > >
> > > > Sander
> > > >
> > >
> > >
> >
>
>
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