. The Astrophysical journal. rk nebulae. The photographs are on exactly the same scaleand show that the two objects are of almost exactly the sameangular size. The first is the nebula 6995 in Cygnus(, a=2o5i, 5=-f-30°4i), the other a dark marking re-cently found by me in Cepheus, in the position: , a— 2o48^,5=+59?6. There is a striking resemblance in the forms ofthe two objects; but one is a luminous nebula and the othera dark—what? One can readily see that if the nebula were tolose its hght, it would, if dense enough, still be shown against thesky and would strongly resembl
. The Astrophysical journal. rk nebulae. The photographs are on exactly the same scaleand show that the two objects are of almost exactly the sameangular size. The first is the nebula 6995 in Cygnus(, a=2o5i, 5=-f-30°4i), the other a dark marking re-cently found by me in Cepheus, in the position: , a— 2o48^,5=+59?6. There is a striking resemblance in the forms ofthe two objects; but one is a luminous nebula and the othera dark—what? One can readily see that if the nebula were tolose its hght, it would, if dense enough, still be shown against thesky and would strongly resemble the dark object. For this andmany other reasons I am constrained to believe that the darkobject is really a non-luminous nebula seen against a luminousbackground. There is no visible evidence of the ordinary nebu-losity in the immediate region of this dark object; that is, thebackground is not the ordinary diffused nebulosity so frequentlyshown on photographs, nor is the stellar stratum dense enough to PLATE II Xortli. Region of Milky Way South of Alpha , Showing Two Dark Objects at Points Indicated lo-inch liruce Telescope. 1910 Oct. i. P^xposure 6*^2^Center at a = 2i8, 5=-|-58?2 (1CS55 o). Scale: icm = DARK MARKINGS ON THE SKY 5 serve as a luminous background. There is every evidence in theoriginal photograph of a continuous, uniform luminosity over thisentire region that is real and not due to the ordinary fogging of theplate by atmospheric luminosity. The idea has therefore suggesteditself to me, and the suggestion has been strengthened by theappearance of other regions, that there is possibly a feeble lumi-nosity in space, sufficiently strong to impress itself on the sensitive?plate by prolonged exposures. I am, of course, familiar with thefact that our atmosphere is more or less luminous and that it fogsthe plate with prolonged exposures, but palpably this could neverserve as a background for the distant nebulae. That the dark nebula of Plate I is betwe
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectspectru, bookyear1895
