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RE : http://www.fer3.com/arc/m2.aspx?i=116534

[NavList] Re: Any "on line" Star Position Computation available ?
From: cfuhb-acdgw---net
Date: 14 Jun 2011 13:54

Dear Paul, and Dear All,

Further to my previous post (http://www.fer3.com/arc/m2.aspx?i=116535) which replied to your post referenced here-above, and further to the subsequent e-mail I sent you earlier to-day, the following info might be of interest to other NavList Readers (Hello to Dave and Andrés !) .

As indicated in my previous e-mail, I fully agree with your explanation given about performing proper motion between 1991.25 and 2000.0 for the HIPPARCOS data. I also fully agree with your numerical results obtained from 1991.25 HIPPARCOS data and transformed into Epoch 2000.0 and which perfectly match the ones I had computed a few years ago.

Nevertheless ... unexplained differences do remain, and I would summarize them as follows :

The discrepancies observed between some Star Catalogs ALL BOIL DOWN TO AN UNEXPLAINED DIFFERENCE BETWEEN THE RESULTS ACCESSED THROUGH VizieR (http://vizier.u-strasbg.fr/viz-bin/VizieR) and the "SUPPOSEDLY SIMILAR" RESULTS ACCESSED THROUGH SIMBAD (http://simbad.u-strasbg.fr/simbad/).

Maintained by the CDS Center in Strasbourg France, these 2 different - nevertheless related - access tools yield different results for the very same reference system and epoch.

Just 2 examples (ALL coordinates herebelow "tagged" with Equator 2000 / Epoch 2000 :

1 - For 1 β Cet

VizieR yields : RA = 00 43 35.371451 Delta = -17 59 11.77811

and SIMBAD yields : RA = 00 43 35.22827 Delta = -17 59 12.0627

2 - For α Ari :

VizieR yields : RA = 02 07 10.407240 Delta = +23 27 44.71195

and SIMBAD yields : RA = 02 07 10.28580 Delta = +23 27 45.9989

As I am totally unable to explain such a "huge" 2 arc second difference when current star catalogs are accurate to some 1/100 arc second, I just sent an explanation request to the Strasbourg CDS Center ( <question@simbad.u-strasbg.fr> ).

I will keep you posted about their reply.

Thanks again for your Kind Attention

Best Regards

Kermit

Antoine M. "Kermit" Couëtte

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