, 1877-09-14
The Opposition Of Mars,

eer'eu Win tne utmost care and assidui-
ty, and with all the appliances at tho
disposal of science. On September & the
planet Mars will be ''in OPPOSITION
that is, he will then be at that point of
the sky which is just opposite the sun, 80
that he will rise at sunset, and come IN
the meridian at midnight. Since both
the planet and the earth sweep in orbits
around the sun, it follows also that at
that time they make their nearest an.
proe"h to each other, and the planet is
then most favorably situated for observa.
ton and examination. In the early au.
tumn Mars will be by far the most con-
spicuous object in the eastern sky, blaz.
ing with red fire hardly inferior to the
brightness of Venus, which by that time
wi" begin to adorn the western twilight,
ana Quit outshining Jupiter. Saturn
close by Mars, will seem comparatively
of no account.
Oppositions Of Mars are not specially
rare. They occur once in about two wears
and fifty days, and if the orbits of this
planet and the earth were perfect circles
the circumstances of all Oppositions
would be essentially alike, and no pe-
culiar interest would attach to one rather
than another. But this is by no means
the case; the orbits are not quite circu-
lar. The earth, about the 1st of july, is
nearly three million miles from the sun
than at New Years; and in the case of
Mars the difference between its greatest
and least distance from the sun is larger
yet, amounting to almost twenty y-eight
millions of miles. The Average distance
between Mars and the earth at the mo-
ment of opposition is about forty-nine
millions of miles; if, however, the oppo-
sition happens when the planet is as far
from the sun as possible and the earth as
near the sun as it can be, they will be
separated by space of sixty-four million
miles; and if, on the contrary, the event
occurs when the conditions are reversed,
the distance between them will be only
thirty-four million, and the opportunity
for observation will be exceptionally ia
vorable. These close oppositions are
rare, the motions of the planet and the
earth being so related that they recur
only at intervals of seventy.nine years,
though some of the intermediate opposi-
tons, separated by periods of fifteen and
seventeen years, are not very greatly in
ferior. The opposition of next Septem-
Der will be one of the best possible, both
earth and planet being nearly in their
most favorable positions, and the distance
between them less than at any time since;
the summer of 170S. The observations
to be made are of two classes-one in e
tended to determine the distance, posi-
ton and motions Of the planet; the other
relating to its magnitude, form, rotation,
surface-markings, and physical constitu
tions.
One subject which deserves, and will
probably receive special attention during
the coming opposition, is that of the plan
cts form. According to some of the best
observers, notably Dawes and Bessel, the
planet is not sensibly tlattened at its
poles; according to others, and decidedly
the numerical majority of observers, 1t is
fsttened very considerably, its polar di-
ameter being nearly 100 miles less than
its equatorial. If, as our textbooks gen
orally assume, this latter result is correct,
it presents a mechanical difficulty of the
gravest character. 1t is quite impossible
to explain how a planet so much smaller
than the earth and with longer day than
ours, can have such form. 1t is hardly
too much to say that (on this assump-
tom theory and fact are hopelessly at
odds.
Probably the measures to be made dur
ing the coming months will explain the
matter; and most likely by showing that
a result obtained by one or two observ-
ers of the first quality is worth more than
that of the multitude.-N. Y. Tunes,