The Indianapolis journal., 1895-07-07

powers of human imagination as the
science Of astronomy We have to brace
our minds to the conception of distances
and magnitudes SO utterly transcending
all ordinary human experience that spe-
cial means have TO be invoked to render
them ineligible. Each advance in our
knowledge of the heavens reveals. to us
the grandeur of the celestial spaces on
an ever-growing scale.
/ propose 10 give in this paper some
Illustrations of what is known with re-
gard TO the distances of the stars. and
shall naturally take the opportunity to
make special use of certain recent ad-
vances by which our knowledge of the
subject has been greatly extended. First
let me say that the task of finding the
distance of star involves the most
delicate piece of measurement that has
ever been undertaken.
The great majority of the stars are
situated at distances so enormous that
it is utterly hopeless to attempt to de-
termine how far away they are. In fact,
only comparatively few stars happen to
lie sufficiently close to the earth to per-
nit of our making an accurate deter
mination of their positions. Nor is it by
any means an easy task to choose out
those particular objects which do lie
within range. 1t not infrequently hap
pens that after much labor has been ex-
pended on observations of some particu-
lar star, it has been found that the work
is fruitless, and that the star is so re-
mote that there is no possibility of
learning what its distance actually
amounts to. Much care must, therefore,
be taken TO make a judicious selection
of the particular star TO which it is pro-
posed TO devote so much time and labor.
1t might naturally be supposed that the
brightest stars are those nearest to the
earth. and no doubt If all the stars were
intrinsically equally bright, then of
course, their apparent brightness would
be safe guide in placing these objects
at their true relative distances. For in
this case the only explanation of the
endless varieties of lustre which stars
exhibit would be that some Of them are
much nearer to US than others But there
is no such simple connection between
brightness and proximity as this would
imply. We know that the very bright
est star in the heavens is Sirius, but we
also know that Sirius is by no means
the nearest neighbor of the solar sys-
tenn. Recent researches have also shown
us that the famous star Arcturus the
brightest member of the constellation
Dootes, and one of the three or four
ern skies, is by no means one of the
stars comparatively near us. Arcturus
has, in fact, been recently shown TO be
so excessively far Off that it must be
classed with those stars whose remote
ness renders ii impossible for US ever to
learn what their distance actually
amounts TO.
ANOTHER METHOD.
There is, however. another indication
OF position which is very frequently ac-
cepted by astronomers when discussing
whether star is likely to lie within
such a degree of proximity to the earth
as TO make it worth their while to try
to determine it's distance. When we are
looking at steamer near the horizon
the vessel seems to change it's place but
slowly, though we know, as a matter OF
fact, that it is travelling at the rate OF
perhaps more than ten miles an hour.
The nearer we are to the steamer the
more rapidly does it seem to move. In
like manner, If star were animated by
what is called proper motion, that is to
say, If the star shifted its position on
the sky with reference to the other
stars, and If the amount OF this shift
was unusually great, then there would
be a presumption that the star was com
paratively near. 1t will, indeed, be OBJ
vious that If all the stars were really
| travelling at the same speed. those which
lie nearest the earth would move over
an appreciable part of the sky in a short
er time than those which were more re-
mote. OF course, we are not entitled tc
assume that the stars are moving with
equal rapidity in space. Indeed, we
know we'll that such is not the case
II But, speaking generally, we may fairly
argue that If star does appear to be
moving rapidly it is a presumption that
that body. is one Of the suns nearest
/ neighbors.
The star whose distance is to be
! sought, having been chosen, an elabo
/ rate series of observations has then tc
be undertaken. The astronomer meas
ures in his telescope the sky interval BY
which that star is separated from q
neighboring star. which, though appar
emily close by, is in reality much further
away. Indeed, for this auxiliary star
we like, If possible, to have an object
which is about ten times as far as the
/ comparatively new star. 1t is, however
essential that the two shall lie so nearly
in the same direction as to be both Wis
ible together in the same telescope field
BY means of a delicate instrument ap
piled TO the telescope We measure tht
width OF the bit of sky between the tive
stars. and these measurements are re
peated night after night for twelve
Il month This years series of observa
tions is absolutely necessary, for tn,
astronomer is gradually shifting his po
sition. and in six months time this shift
will amount to nearly 200. 200 miles
the earth having moved during this pc
riod round TO the opposite point of it,
orbit. The displacement Of the observes
alters the position of the near star IL
relation 10 its more distant companion
We thus find that the sky interval be
tween the two objects changes periodi
cally, and from observations such a
these il is possible, by the magic o
mathematics, TO determine the distance
OF some OF the stars from the earth.
So far as astronomers have ye
learned, the star which lies closest Z
the earth is one which we do not know
in the Northern hemisphere. though /
is very familiar to residents in southern
ATTITUDES. This star is the brightest gen
in the constellation of the Centaur, and
according 10 the usual mode of designa
ton, il is spoken of as Alpha Centauri
The telescope shows the object TO con
sist OF pair of magnificent suns slowl,
revolving each around the other. an
animated by movements in the same di
rection through the sky. Many attempt
have been made 10 determine the dis
tance from us OF this celebrated pair o
objects. Its distance has been measure
b.r nr (.fI1 her MaieSfysS astronomer