The Roanoke times. [volume] (Roanoke, Va.) 1890-1895, 1891-03-18
PHOTOGRAPHING STARS.
Reproducing the Dome Of the
Heavens on'Plates.
How the Instruments Are Manipulated to
* Secure tho Negative of q Stsr-Tn.
teresting Information Conccrn-
Ing tho Art.

Prof. James %. Keller, who is con-
nected with the Lick Observatory in
California, gave IN interesting lecture
at the rooms of the Camera Club In New
York the other evening upon astronom-
zeal photography. He said, observes
O Pittsburgh Dispatch writer, that as
Economical photography presented few
difficulties, and that more knowledge
OF astronomy was required than Of
photography by the observer; in other
words, that the ratio between the two
was about three parts of astronomy to
one part of photography.
II, however, photographer should
attempt to photograph n star he would
find that his image would be blurred,
owing to the movement of the object
during the exposure; therefore it was
necessary that the instrument must be
kept in motion in keeping wisil the mo-
ton of the star, and the apparatus for
Photographic stars, therefore, adjusted
to meet these difficulties. The usual
method of keeping the star on the plate
IN photographing was by moving the
telescope, but owing to the size Of the
instrument Mt the Lick Observatory this
was impossible, as the telescope weighed
seven tons. The plan adopted, there
fore, was to make the plato movable by
means of turning screws.
When the photographer wished to do
some of his work the thing first to be
done was to move the big telescope so
that lens could be capped over the
end. 1t is necessary to put on
2 different lens for Photographic
purposes, and it happens that
IL l., Ia. =
the big telescope. The dry plate
is therefore placed in the tube nine
feet from the eye piece, q hole having
been cut in it for that purpose. A seed
twenty six-platc is used, and for develop
ment an ordinary pyro and potash. The
developer is used very weak and plenty
of time given to bring out the image.
When the plate is developed the opera
tor has to go ut it in blind sort of fash
ion, rs the smaller star images will
not appear till the developing work is
done.
Tho photographs of the planets are
more difficult to secure, owing to the
refraction in the atmosphere. Some
fairly good pictures have, however, been
made of Jupiter and Saturn, and pic
lures of Mars will be taken. Prof.
and the moon, rs we'll us drawings to
illustrate the difference between the
two. The outer ring Of Saturn, which
was not discovered till the big Lick tel
,escopc was turned on the planet, does
not show in the photograph. The pic
lures of the Milky Way which Prof.
Keller has in his collection Of lantern
slides are most excellent, and are the
host IA lion rho % a. ~-
shown on the picture arc none of them
visible to the naked eye.
The photographs of the planet Jupiter
showed plainly the different positions of
the spots and bands on the surface of
the planet, which demonstrate that they
arc constantly changing, and that prob
ably the surface of Jupiter is a mass of
changing matter.
1t is a well-lknown fact that better
photos are obtained through the smaller
telescopes than through the big ones.
Photographing the stars, especially the
small ones, is tedious work, as in some
cases the exposure must last for several
hours. During all that time the plate
or telescope must be moved SO that the
image Of the star will continue in ono
place. The exposure for Il star of the
sixteenth magnitude is two hours, and
only one 1T time can be secured I'M
less the stars happen to be of the same
magnitude, so that getting clusters is
particularly long and tedious in it's ope-
ration.
In procuring the Photographic star
pictures, often what is known as the
1railing process is followed-that is, the
plate is exposed to the star, and then no
snttempt is made to fix the image in one
place, but it passes along over the plate,
making a trail. A number of trails can,
of course, be got on one plate, and then
studied out and measured afterward
The exposures for planets are short
that of "a sun spot taken in Paris was
about as lightning-liloc as possible, the
shutter being attached to the strongest
kind of a spring. The exposure for the
moon takes about IL quarter of a second,
and that for Jupiter about four seconds,
People who visit the Lick Observatory
often ask very remarkable questions in
regard to the telescope as well as to the
methods Of photographing the stars.
The covering of the observatory is made
ofthree-inch steel plates, and, of course, !
is arranged so that a plate can be
moved to allow the telescope to point to
any part of the heavens. visitor who
happened into the observatory when all
the plates were closed asked most car
pestly if the steel plates were transpar-
ent. frequent question asked in re-
gard to star photographing is if fash
light is not used to make the exposure.
There is an old saying that intelligent
Hrcf ~, I,