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|Citation||Barnard, E. E. (1899) Photograph of the Milky Way near the star theta Ophiuchi. Ap.J., 9, 157.|
By E. E. Barnard.
One of the most remarkable and singular regions photographed with the six-inch Willard lens during my connection with the Lick Observatory is that shown in the present picture (Plate II).
To the naked eye Theta Ophiuchi occupies a rather dull region of the Milky Way, which is perhaps made more obscure by the brilliant star clouds southeast of it. If one examines this region with the naked eye, he will see a long dull vacancy, running east and west, to the south of Theta; otherwise the naked eye sees nothing remarkable in the immediate vicinity of the star. The photograph, however, shows that this region is very remarkable, and that certain features shown here do not seem easily explainable without the assumption that the entire ground-work of the Milky Way at this point has a substratum of nebulous matter, though I must confess that it does not look entirely like nebulosity on the plate.
As will be seen, the great dark strip, which is faintly visible to the naked eye, is shown to be an irregular rift in the sheeting of stars, and extending not only south but to the east and north of Theta. North of that star it breaks up into irregular dark apertures, and extends in a straggling manner to the western edge of the plate, from when my photographs show, it extends in a broken manner to the wonderful nebulous region about Rho Ophiuchi, and is connected with the souherly and most distinct of the great vacant lanes near that star.
The peculiarity which I have suggested might imply a nebulous background here, is the singular feature of dark details in the dark rifts and apertures, which are nowhere so remarkably shown as in this plate, though they are noticeable in the
vacancies near Rho Ophiuchi and to the east of the present plate (near 58 Ophiuchi). However, this region, from Rho Ophiuchi to a few degrees beyond 58 Ophiuchi, may be considered as one and the same region, for it is singularly different from any other portion of the Milky Way. Just north of Theta Ophiuchi is a small sharply defined S-shaped aperture in the mass of stars that looks almost like a defect, so distinct does it appear.
These peculiar dark apertures strongly remind one of the appearance sometimes presented in the umbra of Sun-spots, where a darker hole lies in the dark central spot, as if the cavity were partly veiled with some sort of medium that itself had apertures in it – or a hole within a hole.
An earlier photograph of nearly this same region was published in the Photographic Times for August 1895, but I think the present picture, which have never before been reproduced, shows the peculiarities of this part of the sky considerably better than the previous photograph.
March 2, 1899.
Document type: Journal article.
Document source: SAAO Library
Scope: Complete article.
Keyed in: AS
Proof reading: AS
Online version: 2010 August 19.
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