The mirror. (Stillwater, Minn.) 1894-1925, 1920-04-08
ASTRONOMY
No. l. Few Introductory Statements on the Study
of the Sky.
series of papers on astronomy Of sahieh the first ByMrAKS

1t is admitted that not all planets are
habitable. The probability of their habita-
bility depends upon two factors, namely
their present period of plaetary develop
ment and their location from the central
sun about which they revolve and from
which the heat necessary to sustain life is
derived. A planet in an early period of de-
velopment may exist in a semi-molten state,
in which case it could contain no life in any
form such as is known to us, owing to the
intense heat, lack of atmosphere, etc. On
the other hand an "old" planet would pre-
sent objections to the presence of organic
life. In this case the planet might be con-
sidered "dead" planet in that it had lost
its moisture and atmosphere, and under GER
tain conditions might be so cold as to pre-
clude the possibility of any form of life.
How tare the elements, the minerals,
and the gases which constitute the inorganic
matter of other planets known to be similar
to those found upon our earth? OF compar-
atively recent years kindred science to the
science of astronomy has had its birth. This
science is known as spectrology or spectre
scopy, and it is due to the study and know
ledge of this science that the composition of
the planets, suns, and other heavenly bodies
are determined.
Spectroscopy, or the analysis of spectra,
is performed by the aid of an optical instru-
ment known as spectroscope. 1t is a we'll
known physical fact that an optical prism
has the power to disperse, or separate, the
rays of light emanating from a luminous
body into spectrum. A spectrum consists
of series of colors and lines arranged in an
arbitrary sequence according to the wave
length of the various component waves of
light By delicate adjustment of number
of optical prisms and lenses the spectroscope
is enabled to collect, disperse, and project
upon screen, the rays of light emanating
from distant source, sugject to the analysis
of the spectrologist, who by means of this
analysis can determine the composition of
matter in which the light waves have their
source. Each burning and luminous gas,
each mineral and element even the conden-
sation of water, vapor, has its own color or
line in fixed position in the spectrum.
A spectrum may also be obtained by the
use of different form of optical instrument,
known as difraction grating. A large
number of equi-distant lines,-several thou
sands to the inch,-ruled parallel to each
other on plate of glass or metal forms a
dihraction grating. In this case spectrum
is obtained by transmission through glass
grating, or reflection from metal grating /;
the transmitted or reflected light forms a
series of spectra which can be thrown upon
a screen, subject to analysis, or may be ex-
amined by telescope.
Emphatic Importance is placed on the
subject of spectrology since the attainments
of this science cannot be over estimated.
Spectrology has determined the fact that all
the heavenly bodies are closely related, and
by analogy we may reason that they have a
common source.
Of late years astronomical photography
has also played an important part in the
study of the sky. The sensitive photogra-
phic plate records stars and nebulae which
are quite invisible to the eye though aided
by the most powerful telescopes.
In speaking of the distance of any stel-
lar body the distance in terms of miles is
not used. These distances are so great that
our comprehension fails to grasp their magni-
tude. To simplify matters, astronomers use
the term Eight years" where great distances
are expressed. A light year equals the dis
tance that light travels in one years time.
Light has velocity of 10000 miles per
second of time. 1t takes eight minutes for
light from the sun to reach the earth. The
mean distance of the sun from the earth is
100000 miles. Now light year is an
unit of measure equal to $1,000 times this
distance, or $4,000 times 93,000,000 miles.
The constellation of hyra contains the
star Vega, (also known as Alpha Lyrae)
which is the sixth brightest star in the hea-
vens. This star is among those that are the
nearest to the earth. Yet it takes ten years
for light from Vega to reach the earth. II