National Geographic : 1956 Dec
NEW universe, vaster and more filled with star systems than ever believed, unfolds to astronomers with the com pletion of the National Geographic-Palomar Sky Survey. Charting the heavens to the incredible distance of a billion light-years, the survey has expanded known space at least 25 times. New comets and asteroids have shown up within our own solar system. We know more of our home galaxy, the Milky Way. Hun dreds of millions of other galaxies, near and far, have been mapped. Survey Changes Concept of Universe But it is in the far reaches of space, re gions never before charted, that the Sky Survey has made its most significant and exciting discoveries. Clusters of star gal axies, the largest units of matter known, exist there by the tens of thousands. When our work began seven years ago, scarcely three dozen such clusters had ever been seen. To astronomers of the Mount Wilson and Palomar Observatories who have worked on the Sky Atlas, this discovery that clusters of galaxies are all but innumerable has pro vided the greatest of many thrills. It has changed our whole concept of the universe, proving it far more complex than we had thought. To appreciate what these clusters mean, we must understand what galaxies them selves are like. As we look upward on a dark night the stars seem numberless. Yet in the entire heavens only about 6,000 stars are bright enough or near enough to be within range of the human eye. Palomar's 48-inch Schmidt telescope can "see" hundreds of millions of separate stars-all part of what we know as the Milky Way Galaxy. This single system is known to contain more than 100 billion suns. Shaped like a giant Fourth of July pin wheel spinning in space, the Milky Way in astronomical jargon is known as a spiral galaxy (page 785). It is so large that light, traveling 186,000 miles a second, requires a hundred thousand years to cross it from rim to rim. By contrast, light flashes from the moon to the earth in about one and a quarter seconds.