The Washington herald., 1915-09-05

instance. is composed Of three visible
stars. Two of them are close together
while the third revolves about them. But
the motion of the third is irregular and
many astronomers say its irregularity IL
caused by q fourth star in the group which
Is invisible.
The spectroscope has proved q valuable
instrument In the study Of the heavens.
1t is an instrument which permits astrono-
mers to analyze the rays of light given Oh
by stars and to tell what substances there
are in the stars that make these different
rays Of light.
Astronomers have divided stars into
certain broad types as result of spectro-
scopic examination. Type one embraces
the white or blush stars like Sirius and
Vega, which are far more numerous than
other colors. The Milky Way holds two
thirds of these stars. Most of the light
from these stars comes form hydrogen.
Type two consists Of yellowish stars
which have spectra or colored rays like
those Of our sun. Polux and Capella be-
long to this type. Their spectra show
many lines belonging to various metals.
These stars are distributed pretty evenly
over the heavens.
Orange and red stars together with
those which fuctuate in brightness belong
to type three. Their spectra show many
dark bands Type four contains stars that
are few in number faint in light and
generally Of heavy red color.
Besides these stars, more than fifty
others have been discovered whose spec
ira are different in that they contain
bright lines thought to e due to gas that
completely envelops them.
There is large group Of stars which
are inconstant in brightness and these
are called variables. There are at present
more than 400 known variables and new
ones are being found every year Tho
most interesting class of variables are
the temporary stars which appear every
once in while. They blaze up with a
magnificent light and then disappear.
Tycho's star is the most famous Of these.
He first saw 1t on a November night in
1872 and 1t was as bright as Venus II
was visible in broad daylight for severa'
months and then 1t gradually died away.
Another new temporary star and the latest
was discovered in 1892
Astronomers are not sure as to the
cause Of these temporary stars One ex-
PLANTATION they give is that two large
bodies moving swiftly toward each other
just barely miss colliding and create great
eruptions on each other.
The Demon star. which was so named
by the ancients, Is star that takes turns
at being dim. then bright. This 10 caused
by partial eclipse caused by a dark
body. revolving about this star, periodl
cally shutting OF its light and again let.
ting 1t stream forth brightly.
Mira, the Marvellous. In another inter.
esting variable. For 300 years its changes
have been under observation II takes
eleven months completely to 60 through
all its different phases. Most Of the time
1t cannot be seen by the naked eye. Once
In eleven months II reaches its maximum
brightness and after a week begins Ia
sink away again. This Is explained bv
some astronomers as being due to periodi
cal eruptions like those which take place
on the sun. only on an immensely larger
scale.
There are q number Of other variab,ea
which are hopelessiy irregular. scisntista
have puzzled their heads over the freakisA
things that happen to scores Of star. ana
have not q word of explanation for fhem
Perhaps these stars are innataa MIR
enormous sun spots or perhaps tkev coL
iide with meteorfc streams Their .r,si
rotation may account for some thinss an6
great protuberances tor others. Nueh -
astronomers have discovered n the 49,
ems. they know discourasingly littie. Int
astronouers like other scientieta vors
yith : persistsacs thae cuaquers ever
thine