Twice in the course of this discussion we have called attention to the
change of color invariably undergone by temporary stars in the later
stages of their career. This was conspicuous with Nova Persei which
glowed more and more redly as it faded, until the nebulous light began
to overpower that of the stellar nucleus. Nothing could be more
suggestive of the dying out of a great fire. Moreover, change of color
from white to red is characteristic of all variable stars of long
period, such as ``Mira'' in Cetus. It is also characteristic of stars
believed to be in the later stages of evolution, and consequently
approaching extinction, like Antares and Betelgeuse, and still more
notably certain small stars which ``gleam like rubies in the field of
the telescope.'' These last appear to be suns in the closing period of
existence as self-luminous bodies. Between the white stars, such as
Sirius and Rigel, and the red stars, such as Aldebaran and Alpha
Herculis, there is a progressive series of colors from golden yellow
through orange to deep red. The change is believed to be due to the
increase of absorbing vapors in the stellar atmosphere as the body
cools down. In the case of ordinary stars these changes no doubt
occupy many millions of years, which represent the average duration of
solar life; but the temporary stars run through similar changes in a
few months: they resemble ephemeral insects -- born in the morning and
doomed to perish with the going down of the sun.
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