The Princeton union., 1896-10-01
SEEING THE INvISIBLE.
Astronomers Mapping Stars Beyond
the Reach of the TELESCOPES.

Astronomers Mapping Stars Beyond
the Reach of the Telescope.
In the Cosmopo oEtan for September
there is an interesting discussion by
Camille Flammarion of the New Eye
of Science-the sensitive plate Of the
astronomers Photographic apparatus
and Of the international undertaking Of
producing by photography a chart of
the whole heavens. The human eye Is
an admirable instrument, but its pow.
ers are severely limited. 1t sees slow
~. 1t requires for vision a compara-
lively strong light, and it retains no
record of what it has seen. The photo
graphic apparatus of the astronomer,
on the other hand, vastly surpasses
the natural eye in these particulars; it
sees more quickly, has steadier gaze,
reaches forther and makes an uner-
ring record of all its visions. It re-
quires but the -thousandth part of
second for an observation, and with
in that brief period accurately maps
the whole field in view. Directed to-
ward any point in the sky. it discerns
in the depths of infinite space worlds
the human eyes has never seen, and
could never see, even with the aid Of
the best telescope. What the sensitive
plate does not detect, at the first
glance, it beholds after time. In five
one-thousandths of a second it photo
graphs a star Of the first magnitude;
in half a second it includes all smaller
stars to the sixth magnitude; in thir-
teen minutes it has taken in all stars
to the fourteenth magnitude. The hui
man eye is capable of seeing all up to
the sixth magnitude, inclusive Of 49,
59l stars, whereas, the number that
may be mapped by the exposure of the
sensitive plate for thirteen minutes is
over forty millions.
Recently a congress of astronomers
met in Paris to arrange for the concert
ed mapping of the whole heavens,
agreed upon in 1887. Two thousand
years ago Hipparchus made a cata-
logIe of 1922 stars. Present cata-
logues contain over 100000. But the
effort of the astronomical congress is
to make a Photographic chart which
will contain all the thirty or forty mill
ion stars that can be found with the
light gathered by telescope three and
one-half yards long having an object
glass about a foot in diameter. The
work has been divided among sixteen
observers situated at different points
of the globe. Each observatory is to
make 1,200 plates, and each plate pho
tographs two degrees square. AS many
as 11,O2I plates are required to cover
the entire heavens, and the celestial
chart they will be used to construct
will represent sphere having a radius
of over three and half yards. Some
of the plates are to be exposed to the
heavens for five minutes; others for
an hour. The shorter exposure will
give material for a chart to contain
2,5GO,O0O stars.
How many will be revealed by the
longer exposure it is impossible to say
until the 1,O27 sections have been
pieced together and the aggregate
made up after careful inspection. It
will doubtless contain many whose ex-
istence has hitherto been unsupported.
The long exposure will produce rec
| ord of stars, or suns, so distant from
us as to be of the seventeenth or eight
eenth agnitude-stars whose light re-
QulreS millions of years to reach us.
The vast spaciousness of the universe
! viii be evidenced in the minute dots
that reveal to practiced eyes systems
of worlds not previously known. Large
conclusions as to the structure Of the
physical universe will perhaps be sug-
| gested by the great chart when COM
pleted. In itself the chart will be a
monument to the patient labors of sci-
ence and Of the sentiment of fraterni-
ty which enables many different ma
tionS and races to cooperate in its pro.
observation-disclosures Sun.