Re: [guide-user] Star colors/asteroid occn's/Ax.0 concatenation

Chris Marriott Nov 29, 2001

----- Original Message -----
From: "Bill J Gray" <pluto@...>
To: <guide-user@yahoogroups.com>
Sent: Thursday, November 29, 2001 3:20 AM
Subject: [guide-user] Star colors/asteroid occn's/Ax.0 concatenation


> Hi folks,
>
> Ross is right about the 'colored stars' problem: the difficulty here
is
> that Tycho has color data, but GSC (used for displaying stars at fainter
> magnitudes) does not. So when you zoom in far enough, Guide has to swap
> datasets, and the colors go away.

Hi Bill,

Forgive the intrusion - I'm normally just a "lurker" on this mailing list,
but perhaps I can offer a small suggestion in this area?

Is it really necessary to completely swap catalogs when displaying stars? As
you know, Tycho (both 1 and 2) uses the same star numbering system as the
GSC, so it's very easy to tell if a GSC star has a corresponding entry in
Tycho; a GSC star with a designation "xxxx-yyyyy" has a corresponding Tycho
designation "xxxx-yyyyy-1".

When you get below the mag limit of Tycho, why not continue to plot Tycho
stars for the brighter stars, and in addition, display those GSC stars which
aren't in Tycho? That's what my "SkyMap Pro" software does, and the
resulting maps work very well - you get the brighter stars drawn from Tycho
in colour, and fainter stars from the GSC in white. All the program has to
do is look for any Tycho star with a designation ending in "1" and remove
the GSC star with the same designation from the list of stars to be plotted.
Since, by the time you want to activate the GSC, the field of view is
generally fairly small, there normally aren't more than a few hundred (at
most) Tycho stars on the map, and the processing overhead for this
"filtering" process is minimal.

Regards,

Chris
---------------------------------------------------------------
Chris Marriott, SkyMap Software, UK
e-mail: chris@... Web site: http://www.skymap.com
Astronomy software written by astronomers, for astronomers