Introduction

This page focuses on Nicolas-Louis de Lacaille's zodiacal stars catalog from Éphémérides des mouvemens célestes (1765–1775) [2], based on observations performed after his return from the Cape of Good Hope and reduced by the French astronomer Jean Sylvain Bailly, contemporary of Lacaille.

Piazzi's star catalog in Praecipuarum Stellarum Inerrantium [1] has cross-references to this zodiacal star catalog, which is how it came to my attention.

Catalog data

The file zod_data.dat contains the machine-readable version Lacaille's zodiacal star catalog. Its format is documented in ReadMe and it is subject to automatic validation using the Anafile package of the VizieR service.

File name Explanation
ReadMe File descriptions
zod_data.dat Lacaille's zodiacal star catalog
zod_notes.dat Notes on the source catalog

The file zod_notes.dat documents a few issues affecting the catalog, such as erroneous coordinates or star designations, many of which likely typos.

Star identifications

The file zod_ident.dat gives redundant star identifications for the stars of the zodiacal catalog: Bayer / Lacaille and Flamsteed designations; Bright Star, Draper, and Hipparcos catalog numbers. Its format is specified in ReadMe.

File name Explanation
zod_ident.dat Star identifications

The matches were obtained by finding the closest star(s) in the Hipparcos catalog or by default the Henry Draper Catalogue, adjusted to the epoch and equinox of the zodiacal catalog, namely the beginning of year 1765 (Gregorian calendar), or Julian Day 2,365,714 or Besselian epoch B1765.0037… or Julian Epoch J1765.0075…

Some coordinates are clearly erroneous in the catalog. I was able to find a plausible correction and a star match for most of them, relying on the Bayer / Lacaille designations provided by the catalog when present. There remain 5 unresolved cases. These issues are documented in zod_notes.dat.

Accuracy of the catalog

The file zod_ident.dat also gives the differences between Lacaille's positions (reduced by Bailly) and modern positions of the corresponding stars from the Hipparcos or Henry Draper catalog adjusted to the zodiacal catalog's epoch and equinox.

The file 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. 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
Right Ascension
          differences Declination
          differences Distances

The peak of the distance histogram occurs at about 0.15 arcmin, showing that the zodiacal catalog is more accurate by a factor of 2 than Lacaille's southern star catalog from Coelum Australe.

References

[1] Giuseppe Piazzi, Praecipuarum Stellarum Inerrantium Positiones Mediae Ineunte Saeculo XIX. Ex Observationibus Habitis in Specula Panormitana ab anno 1792 ad annum 1813. Palermo: Regia Typographia Militari, 1814.

[2] Éphémérides des mouvemens célestes, pour dix années, depuis 1765 jusqu'en 1775, et pour le meridien de la ville de Paris, Tome VI, Paris: Jean-Thomas Heissant, 1763. Catalogue des 515 Étoiles Zodiacales, observées en 1760 & 1761, par M. l'Abbé de la Caille, & réduites au commencement de l'année 1765, par M. Bailly, de l'Académie Royale des Sciences, pp. lxv-lxxvij.


Acknowledgment. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.