_FOR OCTOBER, 1827._
(_For the Mirror_.)
Mercury is in conjunction with Jupiter on the 7th at noon: he is too
near the sun to be observed this month.
Venus passes her superior conjunction on the 7th, at 10 h. morning,
thenceforward she sets after the sun, and becomes an evening star. This
interesting planet makes a very near appulse to Jupiter on the 16th at
1 h. morning.
Jupiter is in conjunction with the sun on the 18th at 10-3/4 h. evening.
He is afterwards a morning star, preceding the sun in his rising.
The Georgian planet, or Herschel, ceases from his retrograde movement on
the 4th, and appears stationary till the 11th, when he resumes a direct
motion. He is still in a favourable situation for evening observation.
Its great distance from the earth, and the long period of its revolution
round the sun prevent any rapid change in its situation among the fixed
stars; the place therefore which the Greorgium Sidus occupied in
Capricornus in July, (see MIRROR for that month) is so contiguous to
that planet's present position, that the observations then made may be a
sufficient guide for the present month. Its slow motion among the fixed
stars makes it participate in that daily change which is common to them,
hence the planet may be observed in the same place a few minutes earlier
every night. It comes to the south on the 1st at 7 h. 16 min., and on
the 31st at 5 h. 26 min. evening.
The moon is in opposition on the 5th; in apogee on the 11th; in
conjunction on the 20th; and in perigee on the 23rd. She is in
conjunction with Saturn on the 13th at 3-1/4 h. after with Mars on the
18th at 2 h. morning; and Jupiter and Venus on the 20th, with the former
at 1-1/2 h. and the latter at 11 h. afternoon, also with Mercury on the
21st at 10-1/2 h. afternoon.
The Solar luminary is eclipsed on the 20th at 3 h. 47 min. afternoon. He
is above the horizon during the whole time the central shade is passing
over the disc of the earth, but the moon having nearly 2 deg. southern
latitude at the time of true conjunction, in middle of the eclipse, it
will be invisible not only to us but to the whole boreal hemisphere of
the globe. He enters Scorpio on the 24th at 4 h. 36 min. morning.
From the observations made upon the annual eclipses, it appears that the
period of the moon is now shorter, and consequently that her distance
from the earth is now less than in former ages, and this has been
considered as an argument against those who assert that the world may
have existed from eternity; for it was hence inferred that the moon
moves in a resisting medium, and therefore that her motion must by
degrees be all destroyed, in which case she must at last come to the
earth. But M. de la Place has shewn that this acceleration of the moon's
period is a necessary consequence of universal gravitation, and that it
arises from the action of the planets upon the moon. He has also shewn
that this acceleration will go on till it arrives at a certain limit,
when it will be changed into a retardation, or in other words, there are
two limits between which the lunar period fluctuates, but neither of
which it can pass.