Shapley joined the staff of the mount wilson observatory Pasadena California in 1914. Employing the 60-inch reflecting telescope at mount wilson he made a study of the distribution of the globular clusters in the milky way galaxy these clusters are immense, densely packed groups of stars, some containing as many as 1,000,000 members. He found that of the 100 clusters known at the time, one-third lay within the boundary of the constelliation saggitarrius Using the newly developed concept that RR Lyrae variable stars accurately reveal their distance by their period of variation and brightness he found that the clusters were distributed in a sphere.
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