, 1890-02-15
THE CAMERA AND THE HEAVENS
Tho Methods Employed and Cses of Pho
t~ographing the Stars

t~ographinE the stars.
A mariner, who drawing near
port al night, is guided by the two en-
trance lights to the harbor. As he ap-
proaches he sees these two lights sepa-
rate, while when he leaves the harbor
at night the further he gets away the
closer do the lights appear to draw to-
gether. In a similar manner the as
tronomer observes the lights of the uni
verse to learn whittier the great so
lar system is tending. His beacons are
the stars, and in that region toward
which the sun is approaching the stars
seem to spread away from each other,
while in that opposite region from
which the sun is r~etreating the stars
seem to draw in more closely together.
Indeed, it is only by observing these
changes in the apparent places of the
stars that We earn the fact of the suns
motion. To investigate the subject
properly we must employ a large num-
Der OF stars, and we must wait a very
long time in order { o measure their
displacements with precision. This is
exactly b kind of work in which the
photographs may be expected to help
us. Every plate will be carefully
treasured up, TO be compared with the
plates taken in subsequent years, and
from the changes in the apparent
places of the stars we shall learn with
morn accuracy han we have hitherto
been able TO acquire the true facts with
regard to that mighty voyage through
space on which our sun and nl his
system is journeying.
But there are many other aids which
photoe raphy renders to us in our eff
fnrf9 70 Inn -, ~ @l. IL. a.
OF the most difficult problems Is that
of determining the distance of stars.
This depends upon very careful meas
urements made between a star and
other stars in its neighborhood 1t
often takes an hour to measure the ap-
parent distance between two stars In
the ordinary way, lsut in that hour the
telescope might much more profitably
be employed in taking a photograph
on which 100 stars, or perhaps more,
would be found, ard the distance be-
tween every pair OF which would I'D
init of being determined with acru-
racy.
Stlll, other and more marvellous ap-
phcatons of photography to the heav-
have been made. The greatest
telescopes aie often directed to the OBJ
seryation of the nebula. or stains and
patches of light situated at incredible
depths in space. There are thousands
OF these objects known b, those as
tronomers who assiduously cultivate
tins branch of their science, and the
nebutn are all so faint that. with a
single exception, they are invisible to
n unaided eye. The exception is the
Great Nebula, in Andronrda, which
appears like dull spot of light, Just
visible as a glimmer on the darkest
night For ages this object has at
tracted the attention OF astronomers.
n numerous drawings have been
made of IT. But the nature of the
Great NebulH was never understood
until Mr.. Isaac Roberts obtained a mar
yous Photographic picture of the nebu-
lac, after an exposure of four hours. 1t
was then seen to be composed of a
number of rings Of gaseous material,
apparently in a highly heated state.
and doubtless going through some
great process of transformation.
hardly less wonderful is the photo
er.phic picture of the Pleiades. This
well known group of little stars ex-