The Durham recorder. [volume] (Durham, N.C.) 1879-19??, 1909-03-23
DISTANCE OF THE STARS.
How Astronomers Set About the Task
Of Measuring IT..

l.
With the exception of a hundred
stars at most, we know nothing Of
the distances of the individual stars.
What is the cause Of this state of
things? 1t is owing to the fact that
we have two eyes that we are. en-
abled not only to perceive the d.
rection in which external objects
are situated, but to get an idea Of
their distance, to localize them il
space. But this power is rather linn
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 eyaluated be-
comes too small. Instruments have
been devised by which tile distance
between the eyes is, as it were, arti-
ficially increased. With good in
strument of this sort distances of
several miles Inay be eyalnated. For
still greater distances we may i'm
agine each eye replaced by photo
graphic plate. Even this would be
quite sufficient for one Of the heay-
emily bodies-viz, for the moon.
AT one and the same moment let
4 photograph Of the moon and the
surrounding stars be taken both at
Inc Cape observatory and at Che
7oyal 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
lance.
But for the sun ard the nearest
planets, our newt peighbors in the
universe after the moon, the Diff
Guilty recommences.
The reason Is that any available
distance on the earth, taken as eve
distance, is rather sinai. for the
purpose. However, owing to in
credible perseverance and skill 81
several observers and by substitute
ing the most refined measurement
for stereoscopic examination, as
tronomers have succeeded in over
coming the difficulty for the sun.
think We may say that at present
we know its distance to within q
thousandth part Of its amount.
Knowing the suns distance, we gel
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 eve dis.
tanee on our earth. Meanwhile our
success with the sun has provided
us with a new one distance, $4,000
times greater than any possible eve
distance ON the earth. Tor now that
ne know TIE distance at which the
earth travels in It's orbit around the
sun We can take the diameter Of its
orbit Il our -efg distance. Photo
graphs taken at periods six months
apart will represent the stellar
world II seen from points the dis
lance between which is already best
expressed in the time it would take
light 10 traverse ii. The time would
be about sixteen minutes.
However. even this distance, inn
mcnse a. il il. i. on the whole. in
adequate for obtaining % stereo-
SCOPE view OF the stars. II is only
in quite exceptional cases that pho
tcgraphs on large scale-that il.
obtained by the aid Of big tele-
scopcs-show any stereoscopic ef-
feet for fixed stars. By accurate
measurement Of the photos we may
perhaps get somewhat beyond what
We can attain IN simple stcrcoscopic
inspection: but. as we said a mo-
ment ago. astronomers have not sue
ceedcd in this way in determining
the distance 81 more than a hun