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CHAPTER XIV
         OUR SUN A VARIABLE STAR
THE brightest star that we see in the heavens is the
sun. Next after it comes Sirius, but what a gap between!
The sun sends us about ten billion times as much radia-
tion as Sirius. However, things are not what they seem,
for actually Sirius is giving off nearly thirty times as much
radiation as the sun, and only seems fainter because it is
over goo,ooo times as far away. If we could remove the
sun to be a companion star to Sirius, it would seem to be
no brighter than the north star, Polaris.
  It may seem surprising to call the sun one of the stars.
We are accustomed to see the sun as a large round disk,
glowing so intensely that no one can look towards it for
more than an instant. The stars, on the contrary, seem to
us but faint points of light, more like fireflies than like the
effulgent sun. Yet there is no such difference in reality.
It is all a matter of distance.
  Astronomers are now able to measure the distances of
several thousand individual stars fairly well, and by
special methods they can estimate roughly the distances of
millions of others. Knowing the distances, there are sev-
eral methods of finding the diameters of these seeming
points. Those measured thus far range from spheres of the
size of the sun, about 8oo,ooo miles in diameter, to enor-
mously larger ones, no less than 300,000,000 miles in diam-
eter. Thus, our sun, as the late Professor Young very
happily expressed it, "is but a private in the host of
heaven."
  Among the stars there are many which are closely like
the sun. Their light is yellowish like his. The spectro-
scope discloses exactly the same chemical elements in
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