Explosive and Whirling Nebulæ
Too Long; Didn't ReadOne of the most surprising triumphs of celestial photography was Professor Keeler’s discovery, in 1899, that the great majority of the nebulæ have a distinctly spiral form. This form, previously known in Lord Rosse’s great “Whirlpool Nebula,” had been supposed to be exceptional; now the photographs, far excelling telescopic views in the revelation of nebular forms, showed the spiral to be the typical shape. Indeed, it is a question whether all nebulæ are not to some extent spiral. The extreme importance of this discovery is shown in the effect that it has had upon hitherto prevailing views of solar and planetary evolution. For more than three-quarters of a century Laplace’s celebrated hypothesis of the manner of origin of the solar system from a rotating and contracting nebula surrounding the sun had guided speculation on that subject, and had been tentatively extended to cover the evolution of systems in general. The apparent forms of some of the nebulæ which the telescope had revealed were regarded, and by some are still regarded, as giving visual evidence in favor of this theory. There is a “ring nebula” in Lyra with a central star, and a “planetary nebula” in Gemini bearing no little resemblance to the planet Saturn with its rings, both of which appear to be practical realizations of Laplace’s idea, and the elliptical rings surrounding the central condensation of the Andromeda Nebula may be cited for the same kind of proof.