Description
This page addresses the identification of Piazzi's stars in terms of modern catalog designations. I used the same method as in the case of Lacaille's catalog, starting with gathering all the matches by distance (less than 2 arcmin) from the Bright Stars, Henry Draper, Hipparcos, and SAO catalogs (adjusted to the catalog's epoch and equinox, January 1st, 1800 for proper motion and precession), then eliminating "spurious" matches manually while taking into account whether the star is labeled duplex or triplex in the catalog notes. The stars left unmatched were handled on a case-by-case basis.
Many Piazzi stars have no match in the Hipparcos catalog (about 320) or even the Henry Draper catalog (about 20). I used the Durchmusterung catalogs successfully as fallbacks at first, but settled on the SAO catalog since it handled all the cases and provides proper motions, resulting in better position matches.
Once the stars were identified, I added Bayer and Flamsteed designations and star names from the set of reference stars star_ids.dat. About 3000 of Piazzi's stars have no match in that set.
Star identifications
The result is contained in the file ident.dat, described in ReadMe. It collects redundant modern designations for Piazzi's stars.
| File name | Description |
|---|---|
| ReadMe | File descriptions |
| ident.dat | Star identifications |
| dists.dat | Position difference between Piazzi and reference catalogs |
There are no duplicate entries in the catalog.
Of the 7646 stars in Piazzi's catalog, only two remain that I haven't been able to identify: XII.169 and XX.408.
Only five Piazzi star positions differ by more than 1 arcmin from the modern ones: XIV.260, XVI.280, XVII.044, XIX.009, and XX.419. Every such case can be explained by a typographical error on a single coordinate digit that was not caught in the errata. This strikes me as a monumental achievement on the part of Piazzi and his collaborators.
Cross-references
The files below cross-reference Piazzi's catalog with those of Hevelius, Flamsteed, Lacaille, and with the reference star set. They are described in ReadMe.
| File name | Explanation |
|---|---|
| piaref.dat | Cross-references to the reference star set |
| pialac.dat | Cross-references to Lacaille's catalog |
| piaflm.dat | Cross-references to Flamsteed's catalog |
| piahev_o.dat | Cross-references to Hevelius's catalog |
The structure of these files is explained on the corresponding Ptolemy page.
Accuracy of the catalog
The file dists.dat, also described in ReadMe, gives the differences in right ascension (multiplied by the cosine of the declination for normalization), the differences in declination, and the great circle distances, all in minutes of arc, between Piazzi's positions and modern ones (reduced to 1800).
The corresponding histograms below give an idea of the overall accuracy of the catalog (data outside the range of the x axis has been discarded).
| Right Ascension | Declination | Distance |
|---|---|---|
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 |
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The peak of the distance histogram occurs at about 0.06 arcmin = 3.6 arcsec, representing an accuracy improvement by a factor 5 over Lacaille's southern stars catalog and by a factor 2.5 over Lacaille's zodiacal stars catalog.