“ More than 8,000 nebulæ, or star-clusters, closely resembling them, have been found in both hemispheres, and in nearly every constellation. A few, as the great nebulæ of Orion, Argo Navis, and Andromeda, are visible on very clear nights to the naked eye; the rest are telescopic. When greatly magnified some are found to be composed of many thousand remote stars, others remain only as diffused masses of light.
The great nebula of Orion surrounds a multiple star, Theta Orionis, consisting of six, apparently revolving round their common center of gravity. ”