Coulee City dispatch. [volume] (Coulee City, Wash.) 19??-19??, 1935-05-03
DETERMINE SOURCES
OF NIGHT SKY LIGHT
Chicago and Texas College
Professors Make Study.

8V1S00Ok0 AvA01AS SS0yS
Chicage.-Although the huge 82-inch
telescope Of the Mcdonald observatory,
Joint project of the University Of Tex
as and the University of Chicago. on
Mt. Locke, Texas, is not yet completed.
an investigation already Is under way
near the new observatory to determine
the sources Of light in the night sky.
Using an old 12-inch refracting tele-
scope which was presented some years
ago to the Yerkes observatory of the
University of Chicago by Dr. g. F..
Hale, assistant Professor G. T. Elvey
of the Yerkes staff and DR.. F. E. Roach
Of the Mcdonald observatory have
been recording the light of the night
sky with a recording photo-electric
photometer designed by Doctor Elvey.
The light Of the night sky is made
up Of direct starlight; starlight which
Is scattered both by the earth's atmo-
sphere and the matter in interstellar
space; zodiacal light which is concen-
trated in the ecliptic but which may
extend over the entire sky; and of the
light originating within the atmosphere
Of the earth; the permanent aurora.
This aurora is not the polar aurora, or
northern lights, although it is related
to it.
Many Study Problem.
Many Investigators have studied the
problem of the composition Of the light,
and general investigation by the
Dutch astronomer, Van Rhijn has
shown the following percentage COM
position: Direct starlight, IS per cent;
starlight scattered by the earth's atmo-
sphere, per cent; zodiacal light, 43
per cent; aurora, Is per cent, and scat
tered earthlight, 10 per cent.
It is we'll known to astronomers that
there are large fluctuations in some of
the sources Of light, particularly of
the zodiacal light and the aurora Lord
Rayleigh found that the light Of the
night sky undergoes large variations,
with a range Of eight-fold between the
smallest and largest.
The variations are sometimes fairly
rapid, Doctor Elvey having found in his
work at Yerkes as much as a Is per
cent change in brightness Of the sky
within a period of two hours. There
also are daily variations In the inten.
sity Of the auroral light in the night
sky, which in some parts Of the world
reaches maximum about 2 a. m. and
In other parts is at It's maximum just
after twilight has ended.
These large variations have made de-
tailed analysis Of the light difficult, be-
cause during the several hours required
to cover the sky, there are many
changes In the light.
To make possible observations in a
brief space Of time Doctor Elvey de-
vised the recording photo-electric pho
tometer, 1t consists of very sensi-
tive galvanometer which measures the
output Of the amplif1er. The recording
Is achieved by shining lamp on the
galvanometer mirror, which reflects the
light to slit behind which Is q NOV
Ing sheet Of bromide paper.
DenectlonS Recorded.
The reflections of the galvanometer
are then recorded on the bromide pa
per, which is directly connected to the
photometer so that 1t moves past the
slit as the instrument is rotated around
the vertical axis. With this instrument
= complete record Of the brightness of
the sky on circle parallel with the
horizon can be made in approximately
Ave minutes, and the entire sky can
be observed in about an hour. A check
Of the variations in light during this
time can be made by observing a CIV
en-, region of the sky several times.
Doctor Roach already has obtained
qver hundred traclngs with the in
Btrument, from which he and Professor
ElSey have determined the axis Of the
sodiacal light, the cone of light that
can be seen rising from the horizon
latter sunset and before sunrise.
Contrary to general belief. the axis
does not coincide with the plane of the
orbit of the earth-the echptic. OBJ
servations show the morning zodiacal
light is displaced to the north of the
ecliptic by as much as five degrees.
A series of evening observations indi-
cate that in part of the ecliptic the
sodiacal light was near the ecliptic,
apparently crossing 1t.
The astronomers expect that a de-
tailed analysis Of the tracings will give
the relative amount and the distri-
button of the light from various
sources contributing to the total light
from the night sky. &
His Beard Is Passport