The story of the universe. Volume 1 (of 4) : $b The starry skies
History
The story of the universe. Volume 1 (of 4) : $b The starry skies
Astronomy; Earth (Planet); Natural history
Among the red and variable stars, there are many suspected cases
of color variation. Espin and other observers have noted that the
wonderful variable Mira Ceti is much less red at maximum than at
minimum. My own observations confirm this. When at its maximum
brightness, Mira does not seem to me a very highly-colored star,
while at one of its minima I noted it as “fiery red.” Possibly,
however, the great difference between its maximum and minimum
brilliancy may have an influence on estimations of its color. The
remarkable variable Chi Cygni is said to be “strikingly variable in
color.” Espin’s observations in different years show it “sometimes
quite red, at others only pale orange red.” The star Birmingham 118
was described by Schjellerup in 1863 as “decided red,” but it was
found yellow by Secchi in 1868; “bluish” by Birmingham, 1873-76; “no
longer red” by Schjellerup in March, 1876; and “white” by Franks
in 1885. Espin omits it from his revised edition of Birmingham’s
Catalogue.
Birmingham 169 was found red by Struve, blue or bluish-white by
Birmingham in 1874, and white at Greenwich in the same year. Espin
also saw it white in March, 1888. The star Birmingham 30, which lies
close to Phi Persei (54 Andromedæ), was described by Schweizer
as a “red star with a little disk” in January, 1843; Birmingham
noted it as “light red” in December, 1875; Copeland “deep red” in
January, 1876; and Dreyer “reddish” in September, 1878; but Espin,
in November and December, 1887, found it “certainly not red, and
nothing peculiar in the star’s appearance.” It might be expected
that these curious changes of color, if real, would be accompanied
by corresponding changes in the star’s spectrum. Such may be the
case, and observations in this direction would probably lead to some
interesting results.
There seems to be some law governing the distribution of the colored
stars. The white stars appear to be most numerous, as a rule, in
those constellations where bright stars are most abundant, for
instance, in Orion, Cassiopeia, and Lyra; yellow and orange stars in
large and ill-defined constellations, such as Cetus, Pisces, Hydra,
Virgo, etc. The very reddish stars are most numerous in or near the
Milky Way, and one portion of the Galaxy—between Aquila, Lyra, and
Cygnus—was termed by Birmingham “the red region in Cygnus.”
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