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[AZ-Observing] Re: Corwin NGC/IC files at VizieR

From: Brian Skiff <Brian.Skiff@xxxxxxxxxx>
To: az-observing@xxxxxxxxxxxxx
Date: Wed, 11 Aug 2004 00:03:23 -0700 (MST)

     Stan queried:
>>  1. The readme file admits the readings are precise, but not necessarily
>>  accurate....Does this compromise the utility of the files for
>>  professionals and how would professionals use these files of nonstellar
>>  objects? Are they of any value to the amateur? How would an amateur use
>>  them?

     The main thing about the list is that (for essentially the first time)
the historically correct object in the sky has been identified.  The
reason the list was started in the first place was that for large
numbers of the NGC and IC objects, the identification on the sky was
not securely known or reported erroneously in the literature.  An example
is IC 45, which SIMBAD identifies as a galaxy in a group.  The actual
source observations show that it is in fact a faint pair of stars some
4 arcmin away.  So no matter what name you want to give to the galaxy
(UGC 449 would be preferred), it is _not_ IC 45.
     Corwin collected positions from various sources over the years,
but evidently decided---in order to get something out in _this_ lifetime---
to just take grand averages of all the positions rather than selecting
the 'best' single one, or (now) going to recent catalogues and getting
a better one still.  If you actually look at the data, the errors are
only a few arcsec, so for the typical object the identification on the
sky is unambiguous.

>>  2. I'm curious what comprises the multiple measurements of a position.

     For instance, for a particular object Corwin might have micrometric
measurements by Bigourdan from 100 years ago (Bigourdan observed all the
NGC objects accessible to him from Paris and made visual descriptions
as well as the micrometry, all published in six fat volumes).  Then 
Corwin might have a measurement from Pluto camera plates made by me
in the 1980s, and then he might also have the position from the (old)
GSC catalogue.  

\Brian
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[AZ-Observing] Re: Corwin NGC/IC files at VizieR

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