
25-07-2025, 08:08 AM
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star-hopper
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Join Date: Jun 2005
Location: Terranora
Posts: 4,406
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42 nebulae and clusters
OBSERVATIONS OF 42 NEBULAE AND CLUSTERS
While determining the positions of stars for his catalogue, Lacaille also noted the positions of some double stars and nebula. He produced a catalogue of 42 nebulae, which was published in 1755 on his return to France in Memoires de l’Academie Royale des Sciences, 1755. The following is an extract from his journal article, On the Nebulous Stars of the Southern Sky.
“ The Stars which are called nebulous offer to the eyes of Observers so varied a spectacle that their exact and detailed description could occupy an Astronomer for a long time and cause philosophers to make many curious reflections. As strange as are those nebulae that we can see in Europe, those that 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 have greatly wished to give something more detailed and instructive for this article but, other than ordinary telescopes of 15 to 18 feet [4.57 m to 5.49 m] focal length, those that 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 enough time to make these kinds of observations.
“ I first observe that three kinds of nebulae can be distinguished in the heavens;
The first is no more than a whitish, ill-defined area, more or less luminous and of a very irregular shape: these patches are quite similar to the nuclei of faint, tail-less comets. [Most turned out to be globular clusters.]
“ The second class of nebulae comprises Stars which are only nebulous in appearance to the naked eye, but when seen in the telescope, show up as a cluster of distinct stars, although very close to each other. [Usually open clusters.]
“ The third class is that of Stars which are actually accompanied by or surrounded with white patches or by nebulae of the first class.
“ 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 that I have observed them all; especially those of the first and third classes, because they can scarcely be seen except out of the twilight and in the absence of the Moon. However, I believe that the list I give here is passably complete in regard to the more outstanding in these three classes.
“ In frequent examination with a 14-foot [4.27 m] telescope of the areas of the milky way where its whiteness is most noticeable, and comparing them with the two clouds commonly called the Magellanic Clouds and which the Dutch and the Danes call the Clouds of the Cape, it is obvious that the white portions of the sky resemble one another so perfectly that one believes, without too much conjecture, that they are of the same nature, or, if you like, that these clouds are no more than detached portions of the milky way which are themselves composed merely of parts often interrupted. It is not certain that the whiteness of these portions could be caused, as is commonly supposed, by clusters of small Stars, more closely packed than in other parts of the sky, for with such attention as I have observed the better defined extremities, whether of the milky way or of the clouds, I have not seen anything there with a 14-foot telescope, other than a whiteness against the background of the sky, without seeing there more stars than elsewhere, where the background becomes darker.
“ I will not venture further than to suggest that the nebulae of the first class are no more than small portions of the Milky Way, spread throughout different regions of the sky and that the nebulae of the third class are only stars which are found relative to us, in a straight line as we observe these luminous patches.
“ The list which I am going to give here is an extract from the Catalogue of Southern Stars which I put before the Academy: I was not able to distinguish in the Catalogue, the different nebulae except by brief notes which are explained in the discourse which I have included here; but in order to satisfy the curiosity of those who may find these notes too vague, I will give here a short description of each nebula in particular.”
There are 24 open clusters, 7 globular clusters, 7 asterisms, 3 nebula (M8, NGCs 2070 and 3372) and one galaxy (M83) in Lacaille’s catalogue. http://www.messier.seds.org/xtra/history/lacaille.html
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