Smitlisonian Report. 1950. Page 



Messier 13 in the coiistcllal ion Hercules, a nearby example of ilie class of gloV:)ular 

 clusters, each of which has a total candlepower some 30,000 times that of the 

 sun. A more distant globular cluster apj)ears fainter, and from this change in 

 apparent brightness with distance, the distances of the globular clusters can be 

 determined. (Photograph Yerkes Observatory.) 



