Great Cloud

The Milky Way, that river of vague light which flows across the night sky, is actually a disk-shaped galaxy of stars containing probably a hundred billion members, most of them bigger than the sun. Latest estimates of the Milky Way's diameter are about 100,000 light-years (one light-year is about six trillion miles). But there are bigger astronomical aggregations than galaxies. There are groups of galaxies which Harvard's Harlow Shapley, systematizer of the universe, calls super-galaxies or "super-systems" (TIME. July 29). Clusters bigger than super-galaxies he calls metagalactic clouds (metagalaxy is his name for the whole universe).

In Science last week appeared a report announcing discovery and classification of a great stream of galaxies, the greatest of metagalactic clouds. It is 50,000,000 light-years long, 20,000,000 wide. Discovered on plates taken at Harvard's Southern Hemisphere station in South Africa, it lies athwart the sky near the Fouth celestial pole. Fifteen thousand galaxies or "island universes" were counted in it, all of them below the 16th magnitude in brightness. At first the cloud was classed simply as a "major irregularity." But the savants at Cambridge reasoned that it must contain at least 35,000 galaxies not apparent on the photographs, and that such density is not a mere irregularity of distribution but a cosmic entity. Although the great cloud is 100,000,000 light-years from Earth, beyond the reach of all but the most powerful telescopes, it stretches across nearly one-fourth of the sky's arc from horizon to horizon.

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