Juniata sentinel and Republican. [volume] (Mifflintown, Juniata County, Pa.) 1873-1955, 1874-08-12
Miscellany.
Discovering comets.

As the method used by astronomers
in discovering comets Is unknown 10
the general public, short description
NAV be of interest. In making the ob-
seryations a small telescope called
comet seeker, so mounted as TO be
readily moved in any direction,is used.
After deciding in what part of the
heavens TO observe, which is usually IN
the neighbOrhOod of the equator, al
though any part of the heavens may be
used-for comets appear IN all parts
he carefully looks through the instru-
ment. at the same time slowly moving
it in any desired direction, and watches
the stars as they pass. After sweeping
a certain distance he elevates the tele-
scope, so as to include space of the
heavensabove that previously scanped.
Backwards and forwards the comet
seeker is moved, raising the instrument
ON each return so as not to waste time
in looking over the same path. In
these observations he soon may notice,
besides the stars, a faint white cloudy
patch. He has now found eithera neb-
ula or comet. Ii his instrument Is
properly adjusted, he reads the gradu-
alton of the two circles attached TO the
telescope, taking also the time of his
clock, and from them he approximately
knows the objects position. III the
comet seeker Is not III adjustment, he
must then observe through the equa-
tOrial telescope, which Is always so.
Having thus determined the nebula
or comets place, he looks over cata-
lOgue of nebul9. in which are arranged
the position OF all known. The two
Herschels published such catalogue,
containing list of 500, the result of
twelve years of observations. III any
nebula Is found i'll the catalogue having
the same position as the one seen in
the telescope, the objects are probably
identical; but If none Is recorded, the
following observations are made: \
micrometer Is attached to the telescope
to measure the distance of the prob
able comet from two or more of the
brightest stars seen in the instrument,
and If necessary a drawing Is made OF
their relative positions that these stars
may be recognized. After few hours
tLeSe measurements are repeated, and
if there is any difference between them
the object has moved and il must con-
sequently he a comet; but if there is no
motion, it Is IL nebula. BY referring to
a catalogue of fixed stars, the position
of the stars used in these measurements
Is known, and the position of the new
comet can he readily computed from
them by using the previous measure
ments. The position thus obtained, to-
gether with the direction of the comets
motion and its brightness, is immedi-
ately telegraphed to the Smithsonian
Institute. The Institute telegIaphs to
all the American Obseryatories and To
the Royal Observatory, at Greenwich,
England, which in its turn informs
those OF Europe. As observations are
thus made from different places, delays
from cloudy weather are diminished.
The position determined ON three diff
ferent evenings (althOugh in case of
necessity an interval of Il few hours
can be usedD gives sufficient data
to compute the comets orbit. 1t may
seem simple thing to discover a
comet, but it requires considerable skill
and excellent eyesight. This straining
the eye endcavorIng to see such faint
objects Is a great tax on vision. Pa
tience, especially, has to be cultivated.
for one may carry on this work for
months, even for years, without being
rewarded for his work by any dis
COveTy