228 
ASTRONOMY: H. SHAPLEY 
tigations of the brighter stars. The stars of spectral type B, according to 
Charlier, 3 form a flattened system of some 2000 light-years radius, which he 
identifies with the general stellar universe; the group is very small, however, 
as compared with the system now outlined by globular clusters, and we may 
assume instead that these B stars comprise a localized stellar organization. 
To test further for the existence of a limited local cluster, situated far within 
the bounds of the equatorial segment and perhaps comparable in some re- 
spects with other open galactic groups, an investigation has been made of the 
galactic arrangement of the brighter stars. Details of this study are given in 
Mount Wilson Contribution No. 157. In brief, a verification is obtained of 
the presence of a local cluster, for which the following properties are indicated : 
(a) it contains very nearly all the B stars brighter than the seventh magnitude 
(the remainder appearing to be members of the intermingling and surround- 
ing galactic field), a majority of the A stars, and large numbers of those of 
Y in parsecs 
-300 -150 0 +150 +300 +450 
+1001 1 1 1 1 1 
340° 70° 160° 250° 340° 
Galactic Longitude 
FIGS. 4a AND 4b 
Fig. 4a. (Above) Projection of the local cluster of B stars on a plane perpendicular to the 
Galaxy, — adapted from the data shown in Plate IV of Charlier's memoir. The inclination 
of the cluster's central plane to the Galaxy has been partially eliminated by Charlier. 
The projected center of the system of B stars, as derived by him, is at the origin of co-ordi- 
nates; the present work suggests that the central plane of the B stars is much nearer the sun 
(whose position is indicated by the cross) than Charlier supposed. The projection of the 
true galactic plane appears as a broken inclined line, and the distance of the sun and the 
local cluster north of it is to be noted. Short vertical lines across the curve show the limits 
of distance adopted for the solution represented by Fig 46. 
Fig. 4b. (Below.) Solution for the inclination of the local cluster to the galactic plane, 
based upon 400 stars of spectral- type B. Owing to the sun's position to the north, the central 
plane has a dip of 5°. 
redder spectral types; (b) its central plane is not more than 30 light-years 
south of the sun and may be much nearer; on the other hand the true galactic 
plane, as defined by Cepheid variables, faint stars, and the galactic clouds, 
is approximately 175 light-years south of the center of the local cluster (fig. 4a) , 
(c) the central plane, at least for the brighter stars, in inclined about 12° to 
