Abstract
MR. J. H. REYNOLDS delivered his presidential address to the Hoyal Astronomical Society on February 14, taking as his subject the “Galactic Nebulae”. At the moment, it may be said that the limelight of spectacular interest shines more stiongiy on the extragalactic nebulae than on those nebula, more properly so called, which are to be found in our own system, although they present numerous features of great interest. They appear to be actual clouds, and are seen as dark patches in which the background of faint stars is partly or wholly obscured, unless the cloud is illuminated by an adjacent or interior star. If the illuminating star is of early type, the nebula shows a fluorescent emission spectrum excited by the ultra-violet light of the star; but if the latter is late in type, the nebula simply reflects the light. Among the galactic nebulae are numbered the planetary nebulae, which are now considered to have originated as gaseous shells emitted by novae; but no planetary nebula has been found within eight degrees of the position of Tycho Brahe's very bright nova of 1572. Mr. Reynolds dealt with the nature of the dust which causes the colour excess of stars behind clouds and reflects the light of late type stars; owing to the low temperature of interstellar space, the material must be frozen solid, and may consist of particles of frozen water or solid ammonia.
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The Galactic Nebulæ. Nature 137, 308 (1936). https://doi.org/10.1038/137308b0
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DOI: https://doi.org/10.1038/137308b0