Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1890-12-28
PICTURES OF STARS.
How the Dome of the Heavens is Re-
produced on the Plates.
LONG EXPOSURES ARE REQUIRED.
The Telescope Must Move to Compensate
for the Earths Motion.
STORIES ABOUT LICK OBSERVATORY

STVKIES ABOUF LICk ObS6hFAlVkI
Prot James E. Keeler, who is connected
with the Lick Observatory in California,
gave an interesting lecture at the rooms Of
the Camera Club in New York the other
evening upon astronomical photography.
He said that astronomical photography pre-
sented few difficulties, and that more knowl-
edge 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.
If, however, photographer should at
tempt to photograph star he would find
that his image would be blurred, owing to
the movement of the object during the ex-
posure, therefore it was necessary that the
instrument must be kept in motion in keep
ing with the motion OF the star, and the ap-
paratus for photographing 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 in
strument at the Lick Observatory this was
impossible, as the telescope weighed seven
tons. The plan adopted, therefore, was to
make the plate movable by means of turn
ing screws.
SOMETHING ABOUT THE PROCESS.
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. It is necessary to
put on different lens for Photographic pur-
poses and il happens that different focus is
obtained in the big telescope. The dry plate
is therefore placed in the tube nine feet from
the eve piece, ahole having been cut in it for
that purpose A seed-26-p plate is used and for
development the ordinary pyro and potash.
The developer is used very weak and plenty
of time given to bring out the imaga. When
the plate is developed the operator has to go
1t in blind sort of fashion, as the smaller
star images will not appear till the develop
ing work is done.
Smaller stars than can be seen with the
naked eye are located on the dry plate and
brought out by development. This is ow-
ing to the fact that the effect 70 the eve in
looking at a star is immediate and the light
seen as sharp as is possible, but when the
rays are directed on q plate the light is
cumulative and increases on the image till
enough light is gained to fix the star, and Of
course on development it is brought out
clearly. The clear air at Mount Hamilton
makes it more desirable for the uses Of pho
tSgraphy, and many pictures are taken
there. They are mostly small stars, how
ever, and the photographs are made for the
purpose Of measurements.
PHoToGRAPHING THE PLANETS.
The photographs of the planets are moro
difficult to secure, owing to the refraction in
the atmosphere. Some fairly good pic
lures have, however, been made of Jup-
lures Of Mars will be taken.
Prof. Keeler showed pictures of the planets
and the moon. as we'll as drawings to illus
trate the difference between the two. The
outer ring of Saturn, which was not dis
covered till the big Lick telescope was
turned on the planet, does not show in the
photograph. The pictures of the Milky
Way, which Psof. Keeler has in his eollec-
tion of lantern slides, are most excellent,
and are the best ever taken. The hundreds
of stars shown on the picture are 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 are constantly
changing, and that probably the surface OF
Jupiter is mass of changing matter.
IT'S VERY TEDIOUS WORK.
It is a well-known fact that better photos
are obtained through the smaller telescopes
than through the big ones. Photograpning
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 one
place. The exposure for a star of the six
teenth magnitude is two hours, and only
one at time can be secured unless the stars
60 ha If fba ind
getting clusters is particularly long and
tedious in its operation.
In procuring the Photographic star pict-
ures often what is known as the trailing
process is followed, that Is, the plate is e1-
posed to the star, and then no attempt il
made to fix the image in one place, but it
passes along over the plate, making trail
A number of trails can, of course, be got on
one plate, and then studied out and meas
ured afterward.
LENGTH OF THE EXPOSURE.
The exposures for planets are short-thsk
of sun spot taken in Paris was about as
lightning-like as possible, the shutter being
attached to the strongest kind of spring.
The exposure for the moon takes about q
quarter of a second, and that for Jupiter
about four seconds.
People who visit the Lick Observatory
olLen ASK very TeudrkaOle questions IN re-
gard to the telescope as well as to the meth
ods of photographing the stars. The cover
ing of the observatory is made of three-inch
steel plates, and, of course, is arranged 30
that plate can be moved to- allow the
telescope to point to any part of the heav-
ems. A visitor who happened into the OBJ
servatory when all the plates were closed
asked most earnestly if the steel plates were
transparent. A frequent question asked in
regard to star photogrsphing is il a flash
light is not used to make the exposure.
There is an old saying that intelligent men
are the first to lose their wits when entering
an astronomical observatory and seem to
forget the simplest laws. Many cases Of
this have been noticed at the Lick institu-
ton.