Hopkinsville Kentuckian. [volume] (Hopkinsville, Ky.) 1889-1918, 1890-01-03
CELESTIAL pHorooRApHy.
Interesting Facts Explained by tho Astroi
niner KnYal Glr Ireland.

Interesting Facts Explained by tho Astron'
omcr Royal for ireland.
dare say that number of my read.
ers will be surprised TO learn that the
heavens contain multiudes OF invisible
stars. There are, OF course, few
thousand stars that can be seen by the
unaided eye, there are many millions Of
stars that can be seen with tho aid Of q
great telescope, but over and above all
these are myriad OF stars that not
even the keenest of eyes applied to the
biggest and most powerful Of telescopes
will show trace OF. Does not this
seem rather q puzzle. II we can not
see the stars under any circumstances,
how do we know that they are there?
Most assuredly we can not feel their
warmth and as the stars are always ST.
lent they can make no impression on
our sense OF hearing, while our two re-
naming senses Of tasto and of smell
are obviously not OF the slightest as
sistance in the study OF the heavens.
Yet, Notwithstanding that we fail to
perceive those stars directly, we have
the most undoubted evidence OF their
existence.
A star may be so faint that the beam
OF light 1t emits is too feeble to render
1t visible even with all the aid that
great telescopes can give. The instru-
rient collects together the rays and con-
centrates them so that they are all
brought TO point on the sensitive
retina at tho back Of tho eye. II the
rays happen to be sufficiently powerful
to act on the very delicate nerves OF the
eye message is sent from the eye to
the brain and the star Is seen. II, how
ever, the rays are too weak to excite the
retina, then the star is of course not per-
ceived. Under these circumstances, the
only hope of discovering the star is to
substitute for the retina something
which shall be more sensitive to light.
1t has been found that the rays from
one Of these very faint stars when con-
centrated on q point OF a good photo
graphic plate will succeed in making
an impression, provided that suf-
ficiont exposure has been given.
The image on this plate can be
developed and then the star is revealed.
~ YAH AhaHAuti
that the use Of photography is now es-
sential TO astronomical progress. II af-
fords us tho means OF depicting the
magnitudes and the places OF stars
which must otherwise have been quite
unknown to us,
Some one may feel DESTROYS to ask the
same question as was put to me by an
fv,t a1 laA trkar. \ AaaQrfhinO
TO him the way we proceeded; "llow
cen you take photographs OF the stars"
no said, ''for you can only sec them at
night when it is quite dark and yet
every body knows that photographs can
only be obtained when there Is plenty
of light" To explain this difficulty
you must understand what g6es on in
side the camera when the operation is
in progress The glass lenses produce
on the plate an image OF picture of the
object to be represented. In bright day.
light it is the reflected sunlight which
eliminates tho object and enables 1t
TO form the picture. II the object
has light Of its own, as q star has, then
this light will form the necessary i'm
uSt Oh pave anu % Woy
be obtained. 1t is. however, essential
that all light from every source except
that coming directly from the object it,
self shall be carefully excluded, for this
would act on the plate and obliterate
the image. Indeed, when taking phe-
toyraphs Of tho stars We have to take
special precautions to exclude stray
light. | have heard OF plate having
been spoiled by the fact that while it
was being removed from the telescope
after the stars had recorded their i'm
preston carriage drove up the avenue
and flash from the carriage lamp
CHANGED to fall on the plate and COM;
pletely destroyed the faint images Of
tho stars, or course when once the
plate has beon developed It is then as
permanent as photograph taken in the
ordinary way,-Sif Robert &, Bell, In
N. Y. World.