such a spectrum indicates the existence of a very extensive and
very hot atmosphere surrounding the main body, or core, of the
star in question. This particular star is remarkable in that it
has undergone great changes in brilliancy and is located upon a
background of nebulosity. The chances are strong that the star
has rushed through the nebulosity with high rate of speed and
that the resulting bombardment of the star has expanded and
intensely heated its atmosphere.

There are the Wolf-Rayet stars, named from the French
astronomers who discovered the first three of this class, whose
spectra show a great variety of combinations of continuous
spectrum and bright bands. We believe that the continuous
spectrum in such a star comes from the more condensed central
part, or core, and that the bright-line light proceeds from a
hot atmosphere extending far out from the core.

The great majority of the stars have spectra which are
continuous, except for the presence of dark or absorption
lines: a few lines in the very blue stars, and an increasing
number of lines as we pass from the blue through the yellow and
red stars to those which are extremely red.

Secchi in the late 60's classified the spectra of the brighter
stars, according to the absorption lines in their spectra, into
Types I, II III and IV, which correspond: Type I, to the very
blue stars, such as Spica and Sirius; Type II, to the yellow
stars similar to our Sun; Type III, to the red stars such as
Aldebaran; and Type IV, to the extremely red stars, of which
the brightest representatives are near the limit of naked-eye