STAR CLUSTERS AND THElR CONTRIBUTION TO 

 KNOWLEDGE OF THE UNIVERSE. 



By HARLOW SHAPLEY. 

 (Read April 25, 1919.) 



Social relationships among stars are nearly as common as among 

 men and the lower animals. Sidereal bodies completely independent 

 of all star societies are difficult of conception; for the heritage of 

 early and ancestral associations, as well as the immediate environ- 

 ment, influences the present behavior and the destiny of stars. 

 Planetary systems, binaries, groups of three or four nearly equal 

 bodies are thought to be very common — almost universal, it may 

 be ; and the assemblage of stars of all kinds by the tens, hundreds, 

 and thousands into physically organized clusters now appears to be 

 a property of fundamental significance in stellar investigations. 



In considering the aspect of clustering among the fixed stars we 

 see a gradual progression from the largest and most scattered con- 

 stellations to such rich and highly concentrated stellar groups as the 

 globular clusters. Although the constellations were outlined for 

 the most part in prehistoric times and have been used in myths and 

 astrology persistently and universally throughout thousands of years, 

 in general they do not represent definite physical organizations that 

 exclude the stars of neighboring groups; and frequently even the 

 legendary relationships of the stars in the most anciently known con- 

 stellations are traced with difficulty. 



There is, however, among the varied groupings, an easy transi- 

 tion from widely-scattered Ophiuchus and Camelopardalis to Orion, 

 Scorpio, and the Great Bear; and in recent years we have found 

 that the most conspicuous stars of these three last named constella- 

 tions actually form physical stellar systems. The stars of each have 

 motion, colors, and distances much in common, and in each case 

 they have evolved, no doubt, from an origin common in space and 

 in time. From Orion we readily trace the progression in clustering 



PROC. AMER. PHIL. SOC, VOL. LVIII, V, OCT. 21, I919. 337 



