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 a computer program.

Unfortunately, as explained in the introduction of Peters & Knobel [1], 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 five different scanned versions of the catalog.

  • Peters & Knobel's version [1], because Peters seems to have spent a lot of time compiling various manuscripts and attempting to figure out what the original data looked like. I copied it from scratch and compared the result with its previously digitized version [8], which allowed me to detect and correct my initial typos and find several others in [8] as well.
  • Baily's version [2], since Peters refers 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, that I have used consistently across all the versions ("Baily numbers").
  • Manitius's version [3], since it is the source of VizieR's catalog V/61 [7]. It appears that the VizieR version contains quite a few errors in the star identifications, and a few in the star coordinates as well.
  • Halma's version [4], because it has a French translation of the star descriptions. I gave up copying star data from this version not only because the coordinates are given in fraction form, as in the Greek version, and converting them seemed like too much work, but mainly because the star identifications contain too many typographical errors due to confusions between similar characters.
  • Flamsteed's version [5], because I wanted to compare the star identifications in it 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 probably unintentional, but in most 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 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.

 FileName           Lrecl  Records   Explanations
ReadMe                 80            File descriptions
stars_p.dat            74     1072   Ptolemy's catalog from Peters
stars_b.dat            74     1028   Ptolemy's catalog from Baily
stars_m.dat            74     1029   Ptolemy's catalog from Manitius
stars_z.dat            74     1028   Ptolemy's catalog from Flamsteed
descr_p.dat                   1028   Star descriptions from Peters (Latin)
descr_b.dat                   1028   Star descriptions from Baily (Greek)
descr_m.dat                   1028   Star descriptions from Manitius (German)
descr_h.dat                   1028   Star descriptions from Halma (French)
descr_z.dat                   1028   Star descriptions from Flamsteed (Latin)
notes_p.dat                          Notes on Peters'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

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

All the versions provide modern star identifications in the form of Bayer letters, Flamsteed numbers, HR numbers, and others. Some of these identifiers have changed over time. In particular, Baily and Flamsteed use the original lettering of Bayer in Argo Navis (Nav), Centaurus (Cen), Lupus (Lup), Ara, and Corona Australis (CrA), while Peters and Manitius use the "post-Lacaille" lettering. I am planning to convert all these identifiers to a uniform format and publish the result here in the near future. This will allow a straightforward comparison of the star identifiers across all versions (including John Pratt's [6] and the ones from Flamsteed's own catalog).


[1] 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).

[2] 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.

[3] 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).

[4] 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).

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

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

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

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

Acknowledgment. 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.