Historical Star Catalogs

Introduction

The initial project for these pages was to draw the reference Star Maps by constellation, similar to the ones found on the International Astronomical Union's web site, but that I wanted more complete with respect to the Flamsteed and Bayer/Lacaille star designations.

The coordinates for the constellations boundaries were one of the first requirements, which led to the Constellation Boundaries page. Unable to find a complete set of Flamsteed and Bayer star designations, I resorted to Morton Wagman's book Lost Stars [1] and ended up putting Flamsteed's Catalog in machine-readable form. This triggered my interest in digitizing other historical catalogs, examining relashionships between them, and drawing star maps.

Three pages are dedicated to each catalog. The first one provides some historical context, describes the catalog's structure and contents, and links to the related data files. The second page features star maps of the catalog in its own coordinate systems. The third one tackles the identification of the catalog's entries in terms of modern catalogs, either inferred from cross-identifications provided by the catalog's editors, or my own.

Catalog pages

I try to introduce each catalog with background historical information in order to make the pages more pleasant and hopefully instructive to read. However, I'm not a historian of astronomy and a specialist might frown at some statements or notice gaping holes. I'm open to suggestions for improvement.

Beyond that, I have strived to present only verifiable, objective information, or to make it clear when subjective choices had to be made. For instance, the machine-readable versions of the catalogs can be compared to the originals, for which I give my sources. The idea is to allow others to reuse and build on the raw data, while keeping my own interpretations and elaborations separate.

For each catalog, I have attempted to capture as accurately as possible all the content that can be represented in simple structured data files. I have patiently copied and verified the raw data, but there may still be errors (there always are…) and I may have made arbitrary choices. I would appreciate the feedback if an error is detected.

Several editions of historical catalogs contain star identifications made by their authors (e.g., Dreyer, Baily, Knobel). I capture these in their own cross_*.dat files separate from the original catalog data. In accordance with the objectivity goal mentioned above, I leave these cross-references in their raw form, without for instance trying to convert obsolete Bayer designations or adding modern catalog references. This is done separately on the identifications pages (see below).

One of my goals is to facilitate the analysis of catalog data and their cross-references by computer programs. The files should be readily machine-readable. For this reason, I have adopted formats and file descriptions compatible with the conventions for catalogue descriptions of the VizieR service, rather than invent my own. As a bonus, the data files can be subjected to some automatic validation using the Anafile package.

Map pages

The common features of the star maps associated with historical catalogs are described in the following sections. The catalog-specific features are discussed on their own pages.

Representation of catalog stars

The maps represent catalog entries by black or colored disks for stars and light disks with a dotted border for nebulous objects. For stars, the size of the disk varies with the magnitude assigned by the catalog. For nebulous objects, the size corresponds to some fixed, arbitrary magnitude value.

Different versions of a given catalog may be represented on the same maps, using different colors to distinguish versions from each other. In that case, a legend describes the color to version mapping. For some catalogs, corrected star positions or designations are represented in red.

Star designations

Star designations according to the catalog under study are represented. They often consist of a constellation abbreviation and a sequence number or a letter within the constellation.

On maps by constellation, the designation is shown for stars assigned by the catalog to the constellation(s) under consideration and stars assigned to neighboring constellations that fall within its modern boundary. The constellation abbreviation is omitted if it matches the constellation covered by the map.

On other maps, the constellation abbreviation is shown when the constellation assigned by the catalog differs from the modern constellation containing the star.

Reference stars

Reference stars and NGC objects are represented by thin asterisks (for stars) or simplified icons. Star positions, adjusted to the catalog's epoch according to their proper motion and precessed to the catalog's equinox, come from the Hipparcos Catalogue and/or the SAO Catalogue.

For most catalogs, the reference stars are the ones shown on the reference maps and represented by 4-point asterisks. For more recent catalogs (such as Lacaille's), this star set doesn't suffice and the whole Hipparcos and SAO catalogs, up to some cutoff magnitude, are shown. The Hipparcos and SAO stars are represented by incomplete 4-point asterisks that, when combined, look like complete 4-point asterisks as long as the Hipparcos and SAO positions and magnitudes match. This allows fainter stars found in only one of these catalogs to be represented.

Other features

Modern constellation boundaries are represented for reference. The maps by constellation are framed around these boundaries exactly like the reference maps to facilitate the comparison of catalogs to each other or to the reference.

Equatorial, ecliptic, and galactic coordinate lines and points are represented. The equatorial and ecliptic coordinate system correspond to the catalog's equinox and the obliquity of the ecliptic is computed according to the IAU 2006 precession model for the catalog's equinox.

Identifications pages

Identifying the entries of ancient star catalogs can be difficult. In many cases, either no star is found within a short distance of the catalog position, or several plausible matches exist. The catalog position may have been corrupted during the typesetting process, or wrongly transcribed at some point; there may have been a computation error by the catalog's author or an assistant, or the initial observation may have been flawed or wrongly transcribed.

In order to understand what happened to a suspicious catalog entry, it is necessary to return to the original observation notes of the author, and retrace their calculations leading to the reduced catalog position. A daunting task that Francis Baily [3] has accomplished for Flamsteed's catalog and Dennis Rawlins [2] for Tycho Brahe's catalog, for instance.

Otherwise, the identification of uncertain catalog entries involves guesswork and most editors of ancient star catalogs have indulged in it: F. Baily in his collection of ancient catalogs, J. L. E. Dreyer in his edition of Tycho Brahe's catalogs, E. B. Knobel in his editions of Ptolemy's (with C. H. F. Peters) and Ulugh Beg's catalogs, etc. More recently, F. Verbunt and R. H. van Gent have based their star identifications on distances from catalog entries to counterparts in the Hipparcos catalog, which provides very accurate positions and proper motion values, but even so there are cases where guesswork is necessary.

Inevitably, every author chooses identifications that I'm not fully comfortable with. Reluctant to add to the general confusion, I was inclined to represent historical catalog stars on the maps alongside reference stars according to modern catalogs, but without any explicit association between them. Unfortunately, the maps in that state felt incomplete and a little confusing.

So, for each catalog, I have selected my own preferred identifications and presented them and related data on their own pages in order to maintain a clear separation from the more objective catalog pages. The maps use thin dotted lines to connect historical catalog stars to their supposed match(es) in the Hipparcos or SAO catalog, reduced to the catalog's epoch and equinox.

References

[1] Morton Wagman, Lost Stars, McDonald & Woodward Publishing Company, Blacksburg, Virginia, 2003.

[2] Dennis Rawlins, Tycho’s Star Catalog, DIO, Vol. 3, October 1993.

[3] Francis Baily, An account of the Reverend John Flamsteed, the First Astronomer-Royal; compiled from His Own Manuscripts, and Other Authentic Documents, Never Before Published. To which is added his British Catalogue of Stars, Corrected and Enlarged. London, 1835.

Last updated 2026-05-29

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