Evening star. [volume] (Washington, D.C.) 1854-1972, 1909-02-05
DISTANCE OF THE STARS.
How Astronomers Set About Meet
ing and Measuring It.

From the Sclent1nc- American.
With the exception Of hundred stars
at most. we know nothing of the dis
tances of the individual stars
What is the cause of this state of
things? II is owing to the fact that We
have two eyes that we are enabled not
only to perceive the direction in which eX-
ternal objects are situated. but to get an
idea of their distance, TO localiZe them in
space But this power is rather limited.
For distances exceeding some hundreds of
yards It utterly fails. The reason is that
the distance between the eyes as COM
pared with the distance to be evaluated
becomes too small. Instruments have
been devised by which the distance be-
tween the eyes is, it were. artificially
increased. With good instrument of
this sort distances of several miles may
be evaluated. For still greater distances
we may imagine each eye replaced by a
Photographic plate. Even this would be
quite sufficient for one OF the heavenly
bodies viz for the moon.
At one and the same moment let pho
tograph of the moon and the surrounding
stars be taken both at the Cape observa-
tory 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 distance.
But for the sun and the nearest plan
cts. our next neighbors in the universe
after the moon the difficulty recon-
mences.
The reason is that any available dis
lance on the earth. taken as eye-distance,
is rather small for the purpose. However.
owing to incredible perseverance and skill
of seyera, observers and by substituting
the most refined measurement for stereo-
scopic examination. astronomers nave
succeeded in overcoming the difficulty for
the sun. i think We may say that at
present We know its distance TO within a
thousandth part of its amount. Knowing
the suns distance. we get that of all the
planets by we'll known relation exist
ing between the planetary distances.
But now for the fixed stars when must
he hundreds of thousands Of times farther
removed than the sun. There evidently
can be no question OF any sufficient eye
distance on our earth. Meanwhile. our
success with the sun has provided us with
a new eye-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
round the sun. we can take the diameter
Of it's orbit as our eye-distance. Photo
eranbs taken at periods six months apart
will represent the stellar world as seen
from points the distance between which is
already best expressed In the ime IL
would take light to traverse IT, Inc time
would be about sixteen minutes.
However even this distance, immense
az # is is on the whole inadequate for
obtaining a stereoscopic view of the stars.
1t is only in quite exceptional cases that
photographs on a large scale-that is. OBJ
tained by the aid Of big telescopes-show
any stereoscopic effect for fixed stars.
BY accurate mea surement of the photos
we may perhaps get somewhat beyond
what we can attain by simple stereoscopic
Inspection but. as We said moment ago.
CT ronomers have not succeeded in this
way in determining the distance of more
than hundred stars in all.