EVOLUTION OF STARS—ABBOT 179 
besides, a second series growing fainter and fainter as we approach 
the red end of it. 
8. It is well known that the hotter a light source, and the bigger 
it is, the more light it gives. But the two kinds of red stars, being 
the same in color, we must suppose are equally hot on the surface. 
Hence, one kind of them must be enormously bigger than the other. 
Thus, we can now go a step farther and divide our stars into the 
giants and the dwarfs. 
Some of the red giants have been measured in diameter by the 
ingenious method of Doctor Michelson. It proves that they exceed 
200,000,000 miles, or several hundred times the diameter of our sun, 
which itself is a hundred times the diameter of the earth. In fact 
the whole annual orbit of the earth 
around the sun would not extend out to 
the surface of Antares or of Betelgeuse 
if our solar system were centered in 
those stars. 
What must be the state of matter in 
those giant red stars? The answer: In 
the state of an extremely rare gas. For 
by applying Newton’s and Kepler’s fa- 
mous laws of gravitation and planetary 
motion to the cases of the numerous 
double star systems that are known, it 
has been shown that the stars are never 
many times aS massive as our sun. A 
star lke Antares, which has, say, 300 
times the sun’s diameter, has 27,000,000 
times the sun’s bulk. If not more than 
27 times the sun’s mass, it has less than 
toobove the sun’s density. But we know 
that the sun is about 1,500 times more dense than air, so that Antares 
must be something like 1,000 times less dense than air. 
9. We now begin to see a reasonable path in stellar evolution. We 
commence with the formless nebulae, which are of perfectly enormous 
bulk. Some of the stars, though they seem but points to us, are 
shown to be hundreds of millions of miles in diameter. But nebulae 
which are equally distant, since they are clearly star appendages, 
as in Orion and the Pleiades, extend over large areas of sky. Hence 
their bulk is enormously greater than that of stars, too great even 
to try to express. Although no doubt they are excessively rare gases, 
yet doubtless the nebulae would furnish material for many giant 
stars if compressed to the angular dimensions of a starry point as 
seen by us. 
FAINTEST 
TELESCOPIC 
Fie. 1—The range of bright- 
ness of the heavenly bodies 
