Claudius Ptolemy (c. AD 100 – c. 170) wrote a treatise on astronomy known as the Almagest (from the Arabic version of its name) that was the reference work on astronomy for about 1500 years. It contains the most ancient star catalog that we possess and is thought to be an adaptation and possibly an extension of a more ancient catalog composed by Hipparchus more than two centuries earlier.

Ptolemy's catalog contains 1028 entries representing 1025 distinct stars (in three instances, two entries refer to the same star in the context of different constellations). It provides not only the stars' ecliptic coordinates and magnitudes, but also the descriptions of the positions of the stars with respect to the traditional constellation figures drawn in the sky, such as the Big Bear, Andromeda, Capricornus, etc., the so-called 48 Ptolemaic constellations. These descriptions have been more or less adhered to by subsequent celestial cartographers such as Bayer, Flamsteed, Hevelius, Bode, and Argelander.

A lot of ink has already been shed over Ptolemy's work and I don't have anything new to add. As in the cases of the constellation boundaries and Flamsteed's catalog, I just wanted to make available an electronic copy of the catalog as close as possible to the original, without "corrections" or additions of my own. After all, this data has survived for almost 2000 years (even more, if we think that it came from Hipparchus) and it deserves to be treated with respect. It has started in manuscript form, moved to printed form, then to scanned book form, and the natural next step seems to be to move it to electronic data form susceptible of treatment by computer programs.

Unfortunately, as explained in the introduction of Peters & Knobel [2], all the copies and translations of Ptolemy's catalog that have survived are plagued with transcription errors. Several authors have tried to restore a plausible version, with different results. I ended up working with six different versions of the catalog, in scanned or paper form.

  • The star catalog from Toomer's translation of the Almagest [1]. I encoded it from the original (taking the corrigenda on pp. xii–xiii into account) and compared the result with its previously digitized version [8], VizieR's catalog J/A+A/544/A31 for confirmation. The few differences in star positions that I found are documented in notes_t.dat.
  • Peters & Knobel's version [2], because Peters seems to have gone to great lengths to compile as many manuscripts has he could in order to figure out what the original data looked like. For Toomer [1], p.14, it is "still the best treatment of the catalog as a whole..." ("... though badly in need of updating and revision in certain respects", he adds). I copied it from scratch and compared the result with its previously digitized version [10], which allowed me to correct my initial typos and find several others in [10] as well.
  • Baily's version [3], since Peters & Knobel refer to it and Baily has critically examined several printed versions of the catalog. Baily also introduced a very convenient numbering of Ptolemy stars, also used by Peters & Knobel, that I have used consistently across all the versions ("Baily numbers").
  • Manitius's version [4], referred to by Toomer and Peters & Knobel, and the source of VizieR's catalog V/61 [9]. There are just a few differences in coordinates between Manitius and V/61, documented in notes_m.dat, but quite a few in star identifications, of which several look like typos in V/61. John Pratt's version [7], based according to his page on the translation of the Almagest by R. Catesby Taliaferro, is also very close to Manitius's. The few differences in star positions and magnitudes are documented in notes_m.dat as well.
  • Halma's version [5], because it has a French translation of the star descriptions. I gave up copying star data from this version, not only because it required converting the coordinates from fraction to decimal form, but mainly because the star identifications contain too many typographical errors due to confusions between similar characters.
  • Flamsteed's version [6], because I wanted to compare its star identifications with the ones implied in Flamsteed's own catalog, which mentions Ptolemy catalog numbers when possible. It turns out that there are many differences, some of them maybe unintentional, but in many cases as if Flamsteed had changed his mind between the two versions.

Data available on this page

Each catalog is split into a stars-*.dat file with the star identifiers, coordinates, and magnitudes, and a descr-*.dat file with the star descriptions. The stars_*.dat files are pure ASCII files; the descr-*.dat files are UTF-8 encoded due to the Greek characters, the accented and other special characters of French and German, and some special characters in Latin (the browser or text editor may need to be configured to use the Unicode or UTF-8 encoding to display these files properly). This allows the stars_*.dat to be validated based on the file descriptions in ReadMe using the Anafile package of the VizieR service, which doesn't allow non-ASCII characters. The notes_*.dat are free-form files with various observations about the originals.

The following files are available.

File name Explanation
ReadMe File descriptions
stars_t.dat Ptolemy's catalog from Toomer
stars_p.dat Ptolemy's catalog from Peters & Knobel
stars_b.dat Ptolemy's catalog from Baily
stars_m.dat Ptolemy's catalog from Manitius
stars_z.dat Ptolemy's catalog from Flamsteed
descr_p.dat Descriptions from Peters & Knobel (Latin)
descr_b.dat Descriptions from Baily (Greek)
descr_m.dat Descriptions from Manitius (German)
descr_h.dat Descriptions from Halma (French)
descr_z.dat Descriptions from Flamsteed (Latin)
notes_t.dat Notes on Toomer's version
notes_p.dat Notes on Peters & Knobel's version
notes_b.dat Notes on Baily's version
notes_m.dat Notes on Manitius's version
notes_h.dat Notes on Halma's version
notes_z.dat Notes on Flamsteed's version

I have double-checked my work very carefully and I hope that no transcription errors are left. If any are found, I would appreciate the feedback.

Star identificiations

All the versions associate Ptolemy stars with modern star designations in the form of Bayer letters, Flamsteed numbers, HR numbers, or less common catalog identifiers (e.g., Piazzi, Hevelius, Heis, Manitius). Unfortunately, letter assignments have shifted over time due to the contributions of several authors. Most notably, Baily and Flamsteed use the original lettering of Bayer in Argo Navis (Nav), Centaurus (Cen), Lupus (Lup), Ara, and Corona Australis (CrA), while Toomer, Peters, and Manitius use the "post-Lacaille" lettering.

Using Morton Wagman's book Lost Stars as primary reference, I have attempted to convert the designations to a consistent, modern form in order to allow a straightforward comparison of the star identifications across catalog versions. I have tried my best, but I am not overly confident with the result in some difficult cases. The history of some letter assignements is complicated, and it can be hard to figure out which version an author is using. Also, some work remains to be done with the more exotic designations for which I don't have access to the source catalog at the moment.

The result is contained in the file ident_all.dat, where every Ptolemy star is listed along with redundant designations (Bayer, Flamsteed, HR, HD, HIP) of [my interpretation of] the star(s) associated with it by the various authors. To complement it, the files pos_all.txt and mag_all.txt respectively summarize the star coordinates and magnitudes of all Ptolemy stars across the versions (except Flamsteed's catalog, which has its own coordinates and magnitudes). They make differences and commonalities between versions immediately apparent.

File name Explanation
ident_all.dat Summary of file identifications across all versions
pos_all.txt Summary of star positions across all versions
mag_all.txt Summary of star magnitudes across all versions
ident_t.dat Notes on star identifications in Toomer's version
ident_p.dat Notes on star identifications in Peters & Knobel's version
ident_b.dat Notes on star identifications in Baily's version
ident_m.dat Notes on star identifications in Manitius's version
ident_z.dat Notes on star identifications in Flamsteed's version
ident_j.dat Notes on star identifications in John Pratt's version [7]
ident_a.dat Notes on star identifications in Vizier's catalog J/A+A/544/A31 [8]
ident_f.dat Notes on Ptolemy star identifications Flamsteed's own catalog
mapping.dat Bayer to Lacaille mapping in Nav, Cen, Lup, Ara, CrA

The individual ident_?.dat files give brief explanations for my choices of identifiers when they differ from the catalog's, except when there are only trivial differences in Bayer indices. They also contain the list of stars without identification or with as yet unresolved (by me) identification in their respective versions of Ptolemy's catalog. Discussing the accuracy of the identifications is not done here, that task remains to be done.

This work has also resulted in a potentially useful by-product, the file mapping.dat, a tentative but almost complete mapping of the Bayer letters in Nav, Cen, Lup, Ara, and CrA to the Lacaille (and other) letters in use today. I haven't been able to find such a mapping elsewhere so far.

Sources

[1] Ptolemy's Almagest translated and annotated by G. J. Toomer, with a foreword by Owen Gingerich (Princeton University Press, 1998) (pp. 341–399). Available in print.

[2] Ptolemy's Catalogue of Stars - A Revision of the Almagest by Christian Heinrich Friedrich Peters & Edward Ball Knobel (The Carnegie Institution of Washington, 1915), available here and here (pp. 27–50).

[3] The Catalogues of Ptolemy, Ulugh Beigh, Tycho Brahe, Halley, Hevelius, Deduced from the Best Authorities. With Various Notes and Corrections, and a Preface to Each Catalogue. To Which is Added the Synonym of each Star, in the Catalogues of Flamsteed of Lacaille, as far as the same can be ascertained. By Francis Baily (Memoirs of the Royal Astronomical Society, Vol. 13, London, 1843), available here and here.

[4] Des Claudius Ptolemäus Handbuch der Astronomie, a German translation of the Almagest by Karl Manitius, Tome2 (B.G. Teubner, Leipzig, 1912-13), available here (pp. 32–63).

[5] Composition mathématique de Claude Ptolémée, traduite pour la première fois du grec en français, sur les manuscrits originaux de la bibliothèque impériale de Paris., a Greek version and French translation of the Almagest by Nicholas Halma, Tome 2 (H. Grand, Paris, 1816), available here (pp. 33–83).

[6] The version of Ptolemy's catalog contained in John Flamsteed's Historia Coelestis Britannica (London, 1725), available here.

[7] John P. Pratt's page on Ptolemy's Star Catalog, and his electronic version of the catalog.

[8] The VizieR's service Catalog J/A+A/544/A31 by F. Verbunt and R. H. van Gent (2012) is an electronic version of Ptolemy's catalog based on the translation by G. J. Toomer (see also the corresponding article by the authors).

[9] The VizieR's service Catalog V/61 (1987) is an electronic version of Ptolemy's catalog based on the translation by K. Manitius, according to the ReadMe file.

[10] An electronic version (but in HTML) of Ptolemy's catalogue on Brian Tung's site, also mentioned here. This is a transcription of Peters & Knobel's version, with additional data fields. It also appears on the Atlas Coelestis site of Felice Stoppa.


Acknowledgments.

  • This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France. The original description of the VizieR service was published in A&AS 143, 23.
  • This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.