Lacaille Catalogue of Nebulae of the Southern Sky (1755)

17 May 2018

Nicolas-Louis de Lacaille (1713-1762) was one of the greatest and most meticulous observational astronomers of all time, and his astronomical achievement was prodigious. His achievements during his two years at the Cape of Good Hope (1751-1753) alone were incredible, among which was his fabulous 1775 catalogue Sur les Étoiles Nébuleuses du Ciel Austral (On the nebulous Stars of the Southern Sky) which he published in the Memoirs of the Academie des Sciences.

In the catalogue he divided the 42 nebulous objects into three types: ‘Nebulosities not accompanied by stars’, ‘Nebulosities due to clusters’, and ‘Stars accompanied by nebulosity’. There are 14 objects in each part. Today the objects are classified as 23 open clusters, 7 globular clusters, 4 diffuse nebulae, and one galaxy. The other 7 objects are asterisms or stars. (Interestingly, Messier later included seven of Lacaille’s objects in his famous catalogue – namely, M4, M6, M7, M8, M22, M55 and M83.) and talking of M83, among his exceptional discoveries perhaps the most exceptional is M83 – the first galaxy beyond the Local Group to be discovered.

In his report to the Academie des Sciences, Lacaille wrote: “I have found a large number of these three types of nebulae in the southern part of the sky, but I do not flatter myself to think that I have observed them all, especially those of the first and third classes, because they can scarcely be seen out of the twilight and in the absence of the moon. However, believe that the list here is passably complete in regard to the more outstanding in these three classes.”

In the same report he also wrote: “The Stars that are called nebulous offer to the eyes of Observers a spectacle so varied that their exact and detailed description could occupy an Astronomer for a long time and cause philosophers to make curious reflections. As strange are those nebulae we can see in Europe, those which are in the vicinity of the southern Pole concede them nothing, either in number or form. I am going to outline here an account and a list: this essay may help those who have the equipment and leisure to study them with long telescopes. I would greatly wished to give something more detailed and instructive for this article, but, other than ordinary telescopes of 15 to 18 feet focal length, those I had at the Cape of Good Hope were not adequate or convenient for this kind of research. Those who would take the trouble to examine what occupied me during my visit to that country will  easily see that I did not have time to make these kinds of observations.”