CHAPTERS ON THE STARS. 413, 



CHAPTEES OK THE STARS. 



By Professor SIMON NEWCOMB, U. S. N. 

 THE CLUSTERING OF THE STARS. 



A STUDY of Sehiaparelli's planispheres, which we gave in the 

 -^*- last chapter, shows that some regions of the heavens are 

 especially rich in lucid stars and others especially poor. 



Neither telescope nor planisphere is necessary to show that many of 

 those stars are collected in clusters. That the Pleiades form a group 

 of stars by itself is clear from the consideration that six stars so bright 

 would not fall so close together by accident. This conclusion is confirmed 

 by their common proper motion, different from that of the stars around 

 them. The singular collection of bright stars which form Orion, the 

 most brilliant constellation in the heavens, and the little group called 

 Coma Berenices — the Hair of Berenice — also suggest the problem of the 

 possible connection of the stars which form them. 



The question we now propose to consider is whether these clusters 

 include within their limits an important number of the small stars seen 

 in the same direction. If they and all the small stars which they con- 

 tain were within their actual limits removed from the sky, would im- 

 portant gaps be left? The significance of this question will be readily 

 seen. If important gaps would be left, it would follow that a large 

 proportion of the stars which we see in the direction of the clusters 

 really belong to the latter, and that, therefore, most of the stars would 

 be contained within a limited region. The clusters which we shall espe- 

 cially study from this point of view are the Pleiades, Coma Berenices,. 

 Praesepe and Orion. 



The Pleiades. — In the case of this cluster the question was investi- 

 gated by Professor Bailey, by means of a Harvard photograph 2° square, 

 having Alcyone near its center. It was divided into 144 squares, each 

 10' on a side. The brighter stars of the cluster were included within 

 42 of these squares. The count of stars gave the results: 



Within cluster: 1,012 stars, or 24 per square. 

 Without cluster: 2,960 stars, or 29 per square. 



It, therefore, seems that the portion of the heavens covered by the 

 cluster is actually poorer in stars than the region around it. 



Two opposite conclusions might be drawn from this fact. Assuming 

 that the difference is due to the presence of the cluster, we might sup- 

 pose that the latter was formed of material that otherwise would have 



