178 ANNUAL REFORT SMITHSONIAN INSTITUTION, 1926 
Characteristics of typical stellar spectra 
Spectral class B A F 
Sample star__.-.___- Ripe eh 2b 2s he Ae ee Sinise ee ee a Procyon. 
Constellation _______ Orion 0. ere eae Canis’ Maj-__....----___._) Canis ‘Min. 
Colorist sei ye Bee Abe Ne EE ne he WV Ge ition ae Pale yellow. 
Surface temperature! 16,000°--..___....-._____-- AL 000 Moe BA SOD 8,000°. 
Charaeteristics_-____ The few Fraunhofer lines | Hydrogen lines predomi- | Metallic lines conspicuous. 
are mainly of hydrogen nate. Helium lines dis- Are lines of metals 
and helium. Oxygen, appear. Lines of metals appear. 
nitrogen show less con- come in faintly, espe- 
spicuously. cially spark lines. 
Spectral class G Kk M 
rk | 
Sample star____ Sun__._ Rp Ame buss ae sae he 2's! Betelgeuse, 
Constellapign= is eas | Eeenien) BoGtes_ .-| Orion. 
Color 223 258 .| Yellow. Ly UNed dashes ph whist eo? a 0 Red. 
Surface temperature| 6,000°__22_ 2) 8 SUDO Osten ee ters 2,700°. 
Characteristies_____- Solar type. Metallic arc | Sun-spot type. Are lines | Flame lines prominent. 
lines predominate. strong. Flame lines also Heavy absorption bands 
Flaming are lines also conspicuous. Bands of appear and are the con 
conspicuous. compounds appear. spicuous feature, indicat- 
ing spectra of molecules, 
notably titanium oxide. 
7. We must think of the brightness and distances of the stars. 
Nearly 2,000 years ago, in that great fifteenth chapter of St. Paul’s 
Epistle to the Corinthians, he penned the expression, “ For one star 
differeth from another star in glory.” Very accurate measurements 
of this difference have now been made, and it is found that a range 
of more than a billion of billionsfold occurs between the brightness 
of the sun and that of the faintest stars which have been photo- 
graphed with the largest telescope. The accompanying chart (fig. 1) 
shows what an enormous range it is. 
Part of this difference depends on distance. We may express 
these tremendous distances in light-years. Light travels 6,000,000,- 
000,000 miles per year. It takes hght only eight minutes to reach 
us from the sun, four years from the nearest star, and thousands of 
years from the vast majority of them. 
When we know, as we do, the distances of great numbers of the 
stars, it is found that the real brightness of them differs very greatly 
from that which is apparent. Hertzsprung and Russell discovered 
that when ranged in terms of real brightness the different spectrum 
classes behave very differently. The later work of Adams and of 
Jackson and Furner shows this even more in detail. Of deep red 
M stars there are two separate classes, one extremely bright, 
the other extremely faint. Of reddish K stars there are also two 
such classes, not quite so widely separated in brightness. The dis- 
crepancy diminishes with yellow G-type stars, nearly ceases with 
the yellowish F type, and is altogether absent in the white and blue 
stars of types A and B. 
Thus we find our spectrum sequence of star peculiarities split into 
two, <A bright series of stars exists of every spectrum class, and, 
