Public ledger. [volume] (Memphis, Tenn.) 1865-1893, 1882-06-07
About Mercury.
Cincinnati Commercial.

SNASiHhoh NVmmOIcldle
Now that Mercury is in a position
where no one can fail to see it who can
see stars at all before complete dark
ness sets in, a few facts concerning
this member of the solar household
may be of interest.
The unusual favorableness of the
present elongAtion is due to the fact
that the planet reached its greatest
h%eliocentric latitude north and its
greatest angular distance from the sun
Tor this revolution at almost the same
time, the two events having taken
place within less than two weeks of
each other.
The present elongation of 234 deg.
comes within about 4 degrees of being
the greatest angular distance from the
line that Mercury ever reaches.
These two positions being reached at
so nearly the same time, cause the
planet to set al a longer time after the
sun than usual, so that it is visible
for fully an hour after twilight has
sufficiently subsidized to allow Of its Wis
Utility to anyone whose vision is not
very defective.
The nearness Of Mercury to Venus is
a very favorable circumstance forlead-
ing to its detection by eyes that might
overlook it if it we're alone. Venus ia,
now so bright and beautiful in the,
early evening that it can hardly escape
the notice Of even the most unobsery.
ing OF individuals, and when the yes
are directed toward it Mercury can
hardly be missed, as it is very bright
and is only a short distance to the
northward, and somewhat lower.
In addition to the present position
of Mercury, the latitude in which we
are situated is quite favorable for Sc e.
ing it, as the twilight ends earlier
here than it does in higher attitudes.
1t is said that Copernicus, though
he lived to be an old man, and was one
Of the worlds most famous astrono-
mers, died without wei having seen
the planet which any of our readers
who live on or nea this latitude can
SO easily see, as on these evenings, in
company with the beautiful Venus, IT.
adds a charm to the western sky as
twilight fades away. His inability to
see 1t was due to the combined influ.-
ence Of the longer continuance of
twilight in his latitude and the f,,vs
that rose from the Vistula, on the
banks of which river he lived.
Owing to its nearness to the sun
Mercury has been a difficult object
for the astronomer to study in refer
ence to its physical aspects. The
time Of its rotation, its figure and
other things of this nature have mot
as yet been satisfactorily determined.
With our best instruments no mark
ings on the surface Of the planet that.
are clear enough to be used in deter
mining accurately its period of rOta.
ton can be seen, though its period ia
thought to be about twenty-foUr
hours. The chief difficulty in the
way Of getting certain results in this
as we'll as in regard to figure, and the
question of an atmosphere, is in the.
fact that the planet must either be
observed in the daytime, when ~
atmosphere is disturbed by the solar
rays, or in the early evening, whom Il
is SO near the horizon that a'smos.
pheric refraction is an obstacle in tbe
way Of obtaining good results.
AS seen through the telesc one Mer.
curry presents phases very similar to
those of the moon. lea present
phase is very nearly that of the moon
at the quarter, and as it is now be-
ginning to approach inferior genuine
ton its apparent disc will begin To
grow smaller and assume the form Of
q crescent.