[Kstars-devel] Star coordinate inaccuracy -- Hipparcos Epoch bug

[Akarsh Simha]

Hi

I have confirmed the Hipparcos epoch bug that Massimiliano reports.

Massimiliano made this offer earlier -- I'd be grateful if I could get
replacement J2000.0 RA/Dec for all affected stars, under freely
distributable terms.

I think I should be able to work on this the next weekend or so.

Fainter stars don't seem to be affected -- the DSS imagery coincides
with the field of view pretty well.

Brighter stars (especially the brightest, named stars) are certainly
affected. Their coordinates are sometimes off by as much as an
arcminute. Note that seeing fluctuations are of the order of a couple
arcseconds, so an arcminute is a serious error, and not just a catalog
inaccuracy.

However I can also find bright stars that are unaffected. In any case,
it would be good to have a reliable list of stars' coordinates, that I
can use to patch the star catalogs and release them.

Many thanks for finding and reporting this bug, Massimiliano!

OTOH, I noticed that from your mail sometime in 2011, you point out
that deep-sky catalogs are problematic too. I suggest that Steinicke
NGC/IC catalog (downloadable through Download New Data). The
coordinates in the Steinicke catalog are good, because they agree with
DSS imagery as far as I can tell. There are missing magnitudes for
very common objects, since the magnitudes copied over to ngcic.dat for
use in KStars are blue magnitudes, and whenever blue magnitudes are
unavailable, no magnitude is supplied. This means even Messier
globular clusters have no magnitude, as someone recently reported!

I have a "workaround" catalog with me for symptomatic relief, where
I've patched the catalog with visual magnitudes. But the right way to
fix this is a longer procedure -- get KStars to understand magnitudes
in multiple bands, and report only correct data. I've started work on
this already (I added a magnitude hash, except I still haven't written
code to use it!).

Regards
Akarsh