Tables 831 and 832 

 TABLE 831. — Properties and Classification of Star Clusters 



637 



Star clusters fall into two distinctly different types : 



Globular: Typical, Messier 13; open, Messier 4; elongated, Messier 19. Have strong 

 central condensations, rich in faint stars. Scattered widely in latitude, restricted in 

 longitude. Many variables — nearly 900 in 45 clusters. Radial velocities > 100 km/sec. 

 All distant > 10,000, a > 100,000 light-years. Very few new ones found — about 103 

 known. Very definitely part of galaxy. Although concentrated towards its plane, 

 only 2 within 4° of it (cloud obstruction probably). Diameters about 35 parsecs. 

 Many stars, tens and hundreds of thousands. Many giants and supergiants. Max. 

 luminosity about — 2.5. 



Galactic: Very varied : rich, M 11 ; irregular, M 35; nebulous, Pleiades, M 16; accidental, 

 M 103. Almost exclusively in Milky Way, all longitudes ; apparently no variables. 

 Radial velocities rarely > 40 km/sec, generally less. Almost all < 4000 light-years 

 distant. Almost exclusively in galactic region devoid of globulars. Tens and hundreds, 

 rarely thousands of stars. Hyades type, yellow stars as dominant as A type. Pleiades 

 type, almost all B's and A's, on Russell's main branch. 



TABLE 832. — Distribution of Open Star Clusters 



(Trumpler, Bull. Lick Obs., no. 420, 1930. Contains classification in diameters, distances, 

 and distribution of 334 open clusters.) 

 The plane., of symmetry of open clusters is inclined 2?3 to the adopted galactic plane. 

 Its pole lies at R. A. 12 50™. Dec. 2/?7 (1900). Forms much flattened disklike system 

 1000 parsecs thick, diameter 10,000 parsecs. 



Smithsonian Tables 



