The Great Nebula of Orion
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One of the most impressive spectacles in the sky lies on the center of the Sword of Orion. This Sword is adorned with three stars, the central one appearing misty, "like an eye in tears." A large telescope discloses that this is not a star after all but beautiful cloudy masses of nebulæ, which cover the whole central part of the constellation. A photograph uncovers a still further surprise (for the eye of a camera is more sensitive to light than the eye at a telescope), and one sees then that the nebula spreads in all directions, over and beyond most of the stars on the Hunter's figure.
"It is a wonderful sight," says Peck in "The Constellations," "the whole field of view is filled with an irregular mass of green shining mist, which is apparently broken up into flocculent masses, delicate clouds of light, sprays and wisps, and standing out from the cloudy background, like a sprinkling of diamond dust, are seen faint, glittering stars."
Vast masses of dark nebulæ in the Nebula of Orion are also effectively revealed in telescopes. The dark nebula is visible in the photographs as veil-like clouds obscuring the light of the stars beyond them, or, again, as definitely outlined black blotches lying like some huge object on a brilliantly glowing background. Such a 'blotch' is the Dark Bay or Dark Horse Nebula in Orion whose photograph is so fearfully suggestive and wonderfully beautiful.
Nebulous clouds are, in general, dark rather than luminous. These clouds are believed by many astronomers to be cosmic dust-particles driven out from bright stars. These particles finally col-
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