The times. [volume] (Washington [D.C.]) 1897-1901, 1901-01-20
PICTURING THE PLANETS
A Proposition For Photographic
Work Among the Stass.
Ideas of Prominent Astronomer
Concerning the Establishment of "a
Aid of Science Important Re
suits Have Already Been Acquired.

~ the eSta DllSlIneut OF 4 uTdGcn OUStiNd
tory. in connection with the central in
stitution in the city. for the special pur'
pose of Photographic work. Prof Brow
says that the proposed observatory should
be located in a peculiarly rarified atrnos'
phere such as the mountainous region Of
Colorado where the results Obtained would
be much more satisfactory than ut any
station in the country at which, at PIES
ent, Photographic work is being conducted
The immense and generally recognized
Importance which photography now occu-
pies as a feature OF astronomical research
makes it. in the opinion of Prof. Brown,
the greatest desideratum of the work OF
the Naval Observatory. 1t is scarcely pos
sibls to overestimate the scientific value OF
the results constantly being achieved at
other observatories. both in this country
and Europe in the line of stellar photog-
raphy. In Europe there is a cooperative
movement among astronomers for the pho
tographing of the entire heavens, and it is,
in the opinion OF Prof Brown. matter for
regret that this country, for certain rea-
sons. has not been enabled to contribute
toward this gigantic task which. it is eX-
pected. will be completed some time in the
early part of the present century. In va
rious lines of Photographic work, bowev-
er. the United States is proving pre-emi-
nent At Columbia Observatory, for in
stance special facilities have lately been
instituted for the measurement of star
plates which are now being sent from va
rious localities for that purpose. The
faT,
servatory of Minnesota, at which Prof
Leavenworth has conducted some very no.
table work in this lire. The Naval OBJ
seryatory has fine star-measuring appa-
ratus, but it is never used in the meas
urement of star plates for the simple rea-
son that no stellar photographs are made
at the Observatory. The measurement of
these plates is a very interesting process,
involving as it does some of the latest de-
velopments Of astronomical science.
The first step in The measurement of
star photographs is conducted by means
of a special machine. I he plates are neg
alive and the stars are little black dots
on them. Through the centre of plate
are drawn two lines at right angles, and
the last distance Of each dot from both
lines is ascertained and recorded. A we'll
known star was formerly at the centre
of each plate. but ordinarily temporary
mark is put there TO begin with. The
tiny asteroid Eros. which has latlerly be-
come OF intense interest to astronomers.
has been moving through the skies so
rapidly that a change in position among
the stars can be detected in few hours.
The solution of the great problem for
which these observations of Eros have
just been made required the most care
full measurements of the asteroids posi-
ton. as well as that of the stars on each
plate
Undertakings of this kind are often
complicated by the fact that the stars.
though supposed to be stationary, some
times have a motion Of their own. Hence
they cannot be used as standards for COM
paTison until their own position is ac-
curately determined. One Of the neatest
bits of work ever done Of late years was
a set Of observations to determine how
much the earth wabhles on its axis. For
this investigation hfty-eight stars were
employed. An elaborate examination of
star catalogues was found necessary and
an immense amount OF calculation TO de-
termine positively the correct latitude
and longitude of these fifty-eight stand
ards before any variation from their nor
mai position could be detected This i'm
portant preliminary consumed the best
part of three years.
Columbia Observatory, in addition to
its world renewned work in the measure
ment of star plates, has dealt with pho
tographs Of the North Pole region of the
heavens, taken at Helsingfors. Finland,
and the South Polar region, taken at
Cape of Good Hope An offer has been
made to the Royal Observatory at Ley
den similar to that made to several OBJ
servatories throughout the United States
in regard to the measurement of plates
showing the movements of Eros. II is
also understood that arrangements have
beer made for photographing the Plei-
AIDES cluster at a number of foreign OBJ
servatories next year for Columbia, in
order to detect how great are the changes
in the positions of its principal stars
since Rutherford made his celebrated
picture of the same group in 1872
Still another plan for star photogra-
ply, unique In some respects, has been
Instituted by Columbia Observatory. In
order to ascertain with greater accuracy
than ever before the precise location of
the North Pole Of the heavens, il has been
proposed to expose a Photographic
plate to that region during a whole
hight. and let the stars register semi
circular trails thereon. Then by suisse
quent measurement. the common centre
OF the incomplete circles can be found
with great precision. 1t is a mistaken
idea in the minds Of many to suppose that
the so-called Pole Star marks the true
north. Il is more than a degree out of
the way. And further, the arm of the
earth's axis is slowly changing In the
course of twenty-five thousand years IL
describes a circle with a radius of TWEEN
ty-three and half degrees around a
point in the heavens called the pole OF
the elliptic. Now, to keep track of this
shifting pole in the sky, and also to as
certain with precision an irregularity in
the movement, Columbia has provided
LOT a special set Of photographs TO be
taekn at Helsingfors
. The reason of the selection of the latter
somewhat remote locality is very plain. |
Because Of atmospheric refraction 1t is
particularly desirable to get these ric- |
lures in as high a latitude as possible In |
New York the pole is only about 40 de- |
grees above the horizon. while at HeIslng- |
boro It is 90. The Firms have supplied |
the observatory and Columbia with the in |
struments necessary. Being d signed only |
Tor one Kind OF mounting, a costly "equa- |
torial one, which would permit the
movementof the telescope in any direc-
tion. was not necessary. The tube is sup |
ported on pier and fastened in one posi- |
ton with cement. The Instrument is aim
ed directly at the pole, and tilted NJ at
an angleof 60 degrees. This plan was sug- 1
gested by DR.. Jacoby, who is the first |
assistant at Columbia, and who is one OF |
the highest authorities in star-plate
measurement IN the world.
The offers Of Prof. Rees to Lick end |
Leyden were made possible only through |
the interruption OF Columbia's observa-
torial work in consequence of the recent |
change Of site; Just now the institution
is without telescope or observatory.