Abstract
DISTRIBUTION OF SPIRAL NEBUUE.-The distribution of spiral nebula? has been further investigated by Dr. R. F. Sanford, with the aid of photographs obtained with the Crossley reflector (Lick Observatory Bulletin. 297). The photographs were taken with exposures of the order of twelve hours, the object being to find out whether new nebula could be detected in regions of the Milky Way which have hitherto seemed barren of them. They afford no evidence of undiscovered faint nebulae in the regions where they have not previously been found with shorter exposures. It is shown that there is greater average brightness for the extra-galactic than for die galactic spirals, and that the nebula? which lie nearest to the Milky Way are on the average of larger angular size than those away from it. F. G. Brown has shown that the larger nebula? in general are the brighter, but this is not true of spiral nebulas near the Milky Way, which are large and faint. Thus, if angular size be taken as a criterion of distance, it follows that something cuts off the light from the galactic spirals, thereby letting only the nearer ones be perceptible, and then only with diminished brightness. An arbitrary and general distribution of the spiral nebulae can be best harmonised with the observed features of the distribution by assuming the existence of an obstructing medium, which is irregularly scattered throughout the galaxy. It is considered probable that the spirals are not only outside our own system, but that they can have no intimate connection with it dynamically.
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Our Astronomical Column . Nature 100, 52–53 (1917). https://doi.org/10.1038/100052a0
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DOI: https://doi.org/10.1038/100052a0