Description
This page addresses the identification of Ulugh Beg's catalog entries. The general features of these identifications are explained on the corresponding page for Ptolemy's catalog and are not repeated here.
Identifications
The files ident_*.dat listed below contain the identifications according to some editions of Ulugh Beg's catalog as well as the ones retained for the maps and other considerations.
| File name | Description |
|---|---|
| ReadMe | File descriptions |
| ident_b.dat | Identifications according to Baily |
| ident_k.dat | Identifications according to Knobel |
| ident_a.dat | Identifications according to VizieR J/A+A/544/A31 |
| ident_o.dat | Identifications retained for the maps etc. |
| notes_id.dat | Explanation of some identification choices in ident_o.dat |
The file ident_o.dat collects my preferred identifications, for what they're worth. They are represented on the maps and used to establish cross-references to other catalogs. The file notes_id.dat comments on some of my choices. I have followed one author or another in most cases, and tried to remain consistent with my identification choices for Ptolemy's catalog.
Cross-references
The files below cross-reference Ulugh Beg's catalog with Ptolemy's and with the reference star set, according to the identifications in ident_o.dat and the other catalog's corresponding identification files. They are described in ReadMe.
| File name | Explanation |
|---|---|
| begpto_oo.dat | Cross-references to Ptolemy's catalog |
| begref_o.dat | Cross-references to the reference star set |
Again, details about the structure of these files can be found on the corresponding Ptolemy page.
The relations described by the files begpto_oo.dat on this page and ptobeg_oo.dat on the Ptolemy page are mutual inverses. The latter file is similar to pto2beg.dat but addresses the correspondence between Ptolemy's and Ulugh Beg's catalogs from a different viewpoint.
Accuracy of the catalog
The file dists_ko.dat, also described in ReadMe gives the differences between Ulugh Beg's positions (according to Knobel's version) and modern positions of corresponding stars (according to ident_o.dat) from the Hipparcos or SAO catalog, adjusted to Ulugh Beg's epoch and equinox.
| File name | Explanation |
|---|---|
| dists_ko.dat | Differences between Ulugh Beg's positions and modern ones |
It gives differences in ecliptic longitude (multiplied by the cosine of the latitude for normalization), differences in ecliptic latitude, and great circle distances, all in arcminutes. 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).
| Longitude | Latitude | Distance |
|---|---|---|
 |
 |
 |
R. Verbunt & R. H. van Gent [1] have a much more detailed discussion. I just note the position of the peak of the distance histogram at about 20 arcminutes, compare it to 30 arcminutes for Ptolemy, and suggest that Ulugh Beg improves on Ptolemy's catalog accuracy by about one third.