Septembeb 1, 1806.] 



KNOWLEDGE 



201 



EXTENDED NEBULOSITY ROUND ANTARES. 



By Prof. E, E. Babnard, F.E.A.S. i 



IN the Astronomiche Naclirichten, Band 138, Xr. 3301, 

 I have given an account of a sreat nebula near 

 Antares, which is shown on my photographic plates 

 of that region, made with the Willard lens of the 

 Lick Observatory in the spring of 1895. 

 Several photographs of this nebula were secured during 

 the season of its visibility in that year. These pictures 

 show that the sky at that point is quite as extraordinary 

 as the nebula itself. Indeed, the stratum of stars, the 

 long vacant lanes, and the nebula are all so apparently 

 connected that one can hardly doubt that there is an 

 actual connection existing here, and that these objects are 

 but different features of the same phenomenon ; that is, 

 the nebula, the vacant lanes, and the sheeting of stars 

 appear all to be at the same distance and intimately 

 connected. 



From the accompanying photographs it will be seen 

 that the condensations in this nebula occur at certain 

 bright stars — Rho Ophiuchi, 22 Scorpii, and others. From 

 this it is certain that these stars are at the same distance 

 as the nebula, for they form part of it. By inference it 

 would therefore appear that these bright stars are at the 

 same distance as the stratum of small stars through which 

 these vacant lanes run. 



If this is so — and it seems reasonable — these photographs 

 prove what I have held to be the case for many years: that 

 the stars which make up the general structure of the 

 Milky Way are comparatively very small bodies, and that 

 they consequently differ vastly, in point of size at least, 

 from the ordinary stars of the sky. 



The original negatives show that Sigma Scorpii and 

 Antares are also connected with this great nebula by 

 fainter nebulous extensions, though they are not centres of 

 condensation. It would seem, therefore, that not only are 

 the Milky Way aud the nebula here at the same distance, 

 but that many, if not all, of the bright stars in this region 

 are also at about the same distance from us. 



The late lamented A. C. Ranyard, formerly editor of 

 Knowledge, and one of the brightest minds that have 

 adorned the astronomy of to-day, long held that the general 

 stars of the Milky Way were smaller than the average 

 stars of the sky elsewhere. The photographs which I 

 have obtained of the various parts of the MUky Way, I 

 think, prove this in many cases, but in none so emphati- 

 cally as in these pictures of the Antares region. 



One feature about this nebula that seems to distinguish 

 it from the other great nebulosities of the Milky Way is 

 the fact that it strongly condenses about these several 

 bright stars (Rho Ophiuchi, 2'2 Scorpii, and the two small 

 stars Cord. Dur. —24' Nos. 12G83-4), and thus shows un- 

 mistakably its connection with them. The other great 

 nebulosities of the Milky Way seem to be mixed freely with 

 the stars, and not to condense about any individual star. 

 Even in the case of the condensation of the great nebu- 

 losity of 15 Monocerotis, though it is denser at the several 

 bright stars it does not actually condense at any one of 

 these stars. In its manner of condensation at the several 

 bright stars, the great nebula of Rho Ophiuchi resembles 

 the nebula of the Pleiades, for there is an actual con- 

 densation at bright stars, and not alone a simple involving 

 of the stars within the limits of the nebula. 1 have 

 prenously called attention to this peculiarity of mixtures 

 of stars and nebuhr in Astionoimj and Astrophysics. 



" There is one point, however — and it may be an im- 

 portant one — where the Pleiades differ from the rest of 

 these nebulous clusters. In its case the nebulosity is 



condensed about the iudividual stars ; in nearly all the 

 other clusters referred to the nebulosity does not seem to 

 attach itself to any individual star, but simply to involve 

 the group, the stars themselves not showing any special 

 tendency to condensation individually." 



I think this peculiarity of condensation or non-con- 

 densation is an extremely important one, and well worthy 

 of special attention from those who are interested in such 

 subjects. 



In the original photographs of the Antares region there 

 are different degrees of darkness in the vacant lanes that 

 run easterly from the nebula. 



There arc darl: hohs in these vacancies. 



This would seem to show that all this region — lanes 

 and star areas — is covered with a vast diffusion of nebu- 

 losity, and these darker places in the vacant lanes are thin 

 places or holes in this nebulous veiling. However un- 

 explainable these features may be, they are real, and are 

 verified by the different negatives. Indeed, I believe that 

 all this region, as far east as Theta Ophiuchi, is covered 

 by a vast sheeting or substratum of nebulosity. Still east 

 of this is another region where the Milky Way is of & 

 nature wholly different from any other part — that is, it 

 looks like neither stars nor nebulosity, and I believe that, 

 in the ordinary sense of the words, it is neither. 



On the upper part of the unenlarged picture of this 

 region, the star •/- Scorpii is shown to be in a great wing- 

 like nebula— a very remarkable object and unknown pre- 

 vious to the making of these photographs. This nebula 

 does not condense about »-, but extends from it great 

 wings of light. I think I can trace diffusions of this nebula 

 to a connection with the great nebula of Rho Ophiuchi. 

 It is certainly connected with the nebulous mass that is seen 

 to surround the two stars B.D. —19= No. 4358 and —19° 

 No. 4361 (this last star is 18550, 16h. 12m. Is. - 19^ 40■^. 



With a one-and-a-half-inch lantern lens the great nebula 

 of Rho Ophiuchi is shown to extend in a feeble diffusion 

 to several degrees south and west of Antares and Sigma 

 Scorpii. 



The position of Rho Ophiuchi, Yarnallj 6970 for 18600, 

 is in a = 16h. 17m. 12s., 8 = - 23^ 7'. >- Scorpii, Yarnall, 

 6810 for 18000, is a = 16h 3m. 52s., S= - 19^ 6'. 



It would seem that these stars, which are shown to 

 form a part of this great nebula, should be productive of 

 extremely interesting results if investigated with the proper 

 spectroscopic apparatus. 



It will be seen that the great nebula occupies a vacancy 

 here among the thickly strewn stars. From this vacancy 

 dark lanes, with singularly abrupt and well-defined edges, 

 run easterly for many degrees. One of these lanes runs 

 in a broken manner as far east as Theta Ophiuchi, and, 

 sweeping around that star, turns under it westward again, 

 as shown in the photograph pubhshed in Knowlepge for 

 November, 1894. {See also the Astrophysical Journal for 

 December, 1895.) 



I have before called attention to the fact that these 

 great nebula; of the Milky Way either occupy a vacancy 

 among the stars or are on the edges of such a vacancy — 

 such nebuhi', for instance, as the great nebula near 

 a Cygni, that of 15 Monocerotis, the one near J Peisei, and 

 the present one near Antares. This is a very significant 

 fact, that deserves careful attention. 



Kot(ft9 of Boofts. 



The Elements of Physics. By Edward L. Nichols and 

 William S. Franklin. Vol. I., Mechanics and Heat. 

 Pp. 228. Illustrated. (New York ; Macmillan & Co.) 



