Introduction
Nicolas-Louis de Lacaille (1713–1762) was one of the main 18th century French astronomers. During a mission in the southern hemisphere from 1750 to 1754, he established an observatory at the Cape of Good Hope from which he observed and measured the positions of about 10,000 southern stars. This page focuses on the following three publications related to these observations.
☞ Table des Ascensions Droites et des Déclinaisons Apparentes des Étoiles australes renfermées dans le tropique du Capricorne [6] (1756), denoted by [EA] below, an article containing Lacaille's observations of 1935 of the brightest stars and nebulous objects south of the tropic of Capricorn.
☞ Sur les Étoiles Nébuleuses du Ciel Austral [5] (1761), an article describing 42 nebulous objects of the southern sky, referred to as [EN] below.
☞ Coelum Australe Stelliferum [4] (1763), or [CA] below, a book containing the complete set of observations as well as a list of 1942 stars and nebulous objects, including all the ones from [EA], with their positions reduced to the 1750 equinox. This list constittues the most substantial catalog of stars of the southern hemisphere of its time, after the previous attempts by de Houtman (1603), Kepler (1627), and Halley (1679) (see Verbunt & van Gent [1]).
L'Abbé de la Caille
Almost a century later, the reduction of the whole set of Lacaille's observations was undertaken under the direction of Francis Baily. The result was published in 1847 as A catalogue of 9766 stars in the southern hemisphere [3].
In order to classify the newly observed stars, Lacaille creates 14 new constellations to fill the gaps between the existing ones (the Ptolemaic constellations and the southern constellations previously introduced by Plancius, Keyser and de Houtman). With the exception of Mensa, the Table Mountain, he names them after instruments used in the arts and sciences. These constellations are still in use today; they are part of the 88 constellations standardized by the International Astronomical Union in 1930.
Here is their list, with the names as given in Latin on the planisphere at the end of [CA] and in French on the planisphere at the end of [EA].
| Modern Latin name | Lacaille's Latin name | Lacaille's French name |
|---|---|---|
| Sculptor | Apparatus Sculptoris | l'Atelier du Sculpteur |
| Fornax | Fornax chimiæ | le Fourneau |
| Horologium | Horologium | l'Horloge |
| Reticulum | Reticulus | le Réticule Romboïde |
| Caelum | Caelum Scalptorium | les Burins |
| Pictor | Equuleus Pictorius | le Chevalet et la Palette |
| Pyxis | Pixis Nautica | la Boussole |
| Antlia | Antlia Pneumatica | la Machine Pneumatique |
| Octans | Octans | l'Octans de Réflexion |
| Circinus | Circinus | le Compas |
| Norma | Norma | l'Équerre et la Règle |
| Telescopium | Telescopium | le Télescope |
| Microscopium | Microscopium | le Microscope |
| Mensa | Mons Mensæ | Montagne de la Table |
In the manner of Bayer, Lacaille assigns Greek and Latin letters to the stars in the new constellations and to those in the old ones that didn't have any. He also modifies Bayer letters already assigned in Ara, Centaurus, Lupus, Argo Navis and Piscis Austrinus, and he adds Latin letter assignments in Eridanus, Canis Major, Hydra and Sagittarius.
Running out of letters in Argo Navis, he distributes Greek letters to the brightest stars and then splits the constellation into three parts, Puppis, Carina, and Vela (the Stern, the Hull, and the Sails), where he separately assigns upper- and lowercase Latin letters.
Lacaille explains all this and more very clearly in the remarks that follow the catalog of observations in [EA]. Due to the historical interest of this document, I thought it would be worth making an English translation of it. A similar but more succinct text, in Latin this time, concludes [CA]. This one, besides mentioning that the coordinates are reduced to the 1750 equinox rather than observed, does not give the detailed list of 14 new constellations, and omits the final scathing paragraph about Halley's new constellation Robur Carolinum.
Lacaille's constellations and many of his Greek and Latin letter assignments have remained part of the astronomical tradition to this day and originate in these documents. For this reason, I thought that the star catalogs in [EA] and [CA] deserved digitized versions, which I have compiled and made available on this page.
Catalog data
The following files provide the catalog data in machine-readable form.
| File name | Explanation |
|---|---|
| ReadMe | File descriptions |
| lac_data.dat | Lacaille's catalog from [CA] |
| obs_data.dat | Observations from [EA] |
| neb_data.dat | Nebulous objects from [EN] |
| lac_notes.dat | Notes on the source catalogs [CA], [EA], [EN] |
| lac_obs_neb.dat | Mapping between [CA], [EA], [EN] |
Lacaille's catalog from [CA]
Lacaille's catalog of 1942 stars from [CA] is contained in the file lac_data.dat. The file format is described in the ReadMe file and conforms to the the conventions for catalog descriptions of the VizieR service.
The file lac_notes.dat describes the few typos and features of the source catalogs that didn't make it to the digitized version.
According to the title, the positions given in [CA] are reduced ad annum 1750 ineuntem, the beginning of year 1750 (Gregorian calendar), which is
| Julian Day | 2,360,235 |
| Besselian epoch | B1750.0027… |
| Julian epoch | J1750.0068… |
Lacaille's observations from [EA]
The 1935 entries from [EA] are contained in the file obs_data.dat whose format is also described in ReadMe and subject to automatic validation.
The entries in [EA] are not numbered, but I have numbered them sequentially in the file from 1 to 1935 and established the mapping between [CA] and [EA] by finding the star(s) of [CA] whose position most closely matches the position given in [EA]. The positions of a given star in [CA] and [EA] are not supposed to be the same, but they should never differ by more than a few minutes of arc. A single obvious match was found in the vast majority of cases, and a simple visual inspection resolved the few ambiguous ones.
The mapping between [CA] and [EA] is given in lac_obs_neb.dat described in the file ReadMe. All the entries in [EA] have a match in [CA] but 7 entries in [CA] don't have a match in [EA]. Discrepancies in letter assignments and gross differences in positions are described in lac_notes.dat.
Nebulous objects from [EN]
The file neb_data.dat contains the designations and coordinates of the 42 objects from [EN]. To avoid file clutter, it also includes the object descriptions, in French, UTF-8 encoded. Its format is specified in ReadMe and it is subject to automatic validation, provided that the descriptions starting at column 25 be trimmed off, since the Anafile package of the VizieR service doesn't support non-ASCII characters.
There is more information about Lacaille's nebulous objects at the SEDS page on Lacaille [2].
All the nebulous objects from [EN] have counterparts in [EA] and [CA], but a couple of nebulous objects from [EA], including one from [CA], don't appear in [EN]. The coordinates are sometimes a little different between these sources. These cases are documented in lac_notes.dat and the mapping between [EN] and [CA], [EA] is included in lac_obs_neb.dat.
References
[1] F. Verbunt & R. H. van Gent, Early star catalogues of the southern sky, Astronomy & Astrophysics, 530, A93, 2011.
[2] Hartmut Frommert & Christine Kronberg, Lacaille's "Catalog of Nebulae of the Southern Sky" at the Messier pages at SEDS.
[3] Francis Baily (ed.), A catalogue of 9766 stars in the southern hemisphere, for the beginning of the year 1750, from the observations of the Abbé de Lacaille made at the Cape of Good Hope in the years 1751 and 1752, Taylor, London, 1847.
[4] Nicolas-Louis de la Caille, Coelum Australe Stelliferum seu Observationes ad Construendum Stellarum Australium Catalogum institutae, in Africa ad Caput Bonae-Spei, Guerin & Delatour, Paris, 1763.
[5] M. l'Abbé de la Caille, Sur les Étoiles Nébuleuses du Ciel Austral, Histoire de l'Académie royale des sciences, Année 1755, pp. 194–199. Imprimerie royale, Paris, 1761.
[6] M. l'Abbé de la Caille, Table des Ascensions Droites et des Déclinaisons Apparentes des Étoiles australes renfermées dans le tropique du Capricorne: observées au cap de Bonne-espérance, dans l'intervalle du 6 Août 1751, au 18 Juillet 1752, Histoire de l'Académie royale des sciences, Année 1752, pp. 539–592. Imprimerie royale, Paris, 1756.