The Florida star., 1909-07-09
DISTANCE OF THE STARS.


Hsw AstroRensrs Get About ths Task
- Measuring n.
With the exception Of hundred
stars at most, We know nothing Of
the distances Of the individual stars.
What IL the cause Of this state Of
thingsi It is owing to the fact that
we have two eyes that we are en-
abled not only to perceive the di-
rection IN which external objects
are situated, but to get an idea of
their distance, to localize them In
space. But this power is rather lin
tied. For distances exceeding some
hundreds of yards it utterly fails.
The reason is that the distance be-
tween the eyes as compared with
the distance to be evaluated be-
comes too small. instruments have
been devised by which the distance
between the eyes is, as it were, arti-
6cially increased. With a good in
strument of this sort distances of
several miles may be evaluated. For
still greater distances we may i'm
agine each eye replaced by a photo
graphic plate. Even this would be
quite sufficient for one of the heav-
enly bodies-viz, for the moon.
At one and the same moment let
a photograph of the moon and the
surrounding stars be taken both at
the Cape observatory and at the
Royal observatory at Greenwich.
Placing the two photographs side by
side in the stereoscope, we shall
clearly see the moon Hanging in
space" and may evaluate its dis
tance.
But for the sun and the nearest
planets, our next neighbors in the
universe after the moon, the diff
Guilty recommences.
The reason is that any available
distance on the earth, taken as eye
distance, is rather small for the
purpose. However, owing to in
credible perseverance and skill of
several observers and by substitut-
ing the most refined measurement
for stereoscopic examination, as
tronomers have succeeded in over
coming the difficulty for the sun. 1
think we may say that at present
we know its distance to within q
thousandth part of its amount.
Knowing the suns distance, we get
that of all the planets by a well
known relation existing between the
planetary distances.
But now for. the fixed stars,
which must be hundreds of thou
sands Of times farther removed than
the sun. There evidently can be no
question of any sufficient eye dis
tance on our earth. Meanwhile our
success with the sun has provided
US with a new one distance, $4,000
times greater than any possible eye
distance on the earth, for now that
we know the distance at which the
earth travels in its orbit around the
sun we can take the diameter of its
orbit as our eye distance. Photo
graphs taken at periods six months
apart will represent the stellar
world as seen from points the dis
tance between which is already best
expressed in the time it would take
light to traverse it. The time would
be about sixteen minutes.
However, even this distance, i'm
mense as it is, is, on the whole, in
adequate for obtaining a stereo-
scopic view of the stars. 1t is only
in quite exceptional cases that pho
tographs on a large scale-that is,
obtained by the aid of big tele-
scopes-shOw any stereoscopic eff
feet for fixed stars. By accurate
measurement of the photos we may
perhaps get somewhat beyond what
we can attain by simple stereoscopic
inspection; but, as we said a mo-
ment ago, astronomers have not sue
ceeded in this way in determining
the distance of more than a hun
dred stars in all.-Scientifc Ameri-