Call 



Hell 



-.i 



Cal 



1. Spectra of main sequence stars (05 to K2). The bright lines of iron in the comparison 

 spectrum at the bottom can be matched with dark hnes in the coolest stars. 



Ca 1 1 



Sr II 



Sr I! 



BO 



B5 



AO 

 A5 



F2 

 F8 

 G2 

 K2 



Ml 



2. Spectra of supergiant stars (BO to Ml). Note the sharpness of the hydrogen Hnes 

 compared with figure 1, above. (Photographs on this page by RadcHffe Observatory 

 X 10, from Astronomical Spectroscopy, by A. D. Thackeray.) 



