The Temperature-Luminosity Diagram 
61 
56, 57] 
Absolute Bolometric Magnitude 
Giants and Dwarf Stars. 
57. In 1905 Hertzsprung* discovered that the red stars fell into two 
distinct classes, one of which he called Giants on account of their great size, 
Effective Temperature 
Fig. 5. Effective Temperatures, Absolute Bolometric Magnitudes and Radii of Stars. 
©—Stars within four parsecs of Sun. 
x—More distant stars. 
and the other Dwarfs on account of their small size. This division is clearly 
shewn in our diagram, there being no itT-type stars of magnitudes between 
* Zeitsch. fiir Wissenschaftliche Photog. hi. p. 442. See also v. p. 86, and Ant. Nach., Iso. 4296.