Public ledger. [volume] (Memphis, Tenn.) 1865-1893, 1882-10-04
The Transit of Venus.

AAAAdN0ipuAt Alhutns
The next great astronomical event
is the transit of Venus, which will
occur December 6, and will last six
hours. Although the sun is said to
rise in the east, it is noticeable that in
summer he rises further north than in
winter. The extreme northern point
Of rising marks the tropic OF Cancer
aud the southern indicates the tropic
of Capricorn. Between these two
points the sun appears to Oscillate. AS
the earth revolves around the sun he
to mark out a path across the
sky; this apparent path is called the
"ecliptic." To a person at the equator
the sun rises alternately in the north
east and in the southeast. This change
is gradual, of course, and requires six
months to complete it. After touch
log the tropic Of Capricorn he recedes
and in six months more or one year
more from the time of leaving Cancer,
he returns to it. AS the sur is the
center of our system he is relatively
stationary.
The cause of his apparent change Of
place must then be in the earth, and
the reason is that the ecliptic and our
equator do not coincide, tina is, they
are not plumb as the tires and felloes
of wheels are. The axis of the earth
is not perpendicular to the ecliptic,
but is at an angle, and astronomers
call this angle the "obliquity" of the
earth's axis. 0bliquisy of axis also
partially accounts for the apparent
movements Of planets.
Sometimes Mercury and Venus pass
directly between the earth and Gun and
appear to glide ever his disc; these
phenomena are called "transits." The
word transit is technically applied ia
Mercury aud Venus, a transit of the
moon being called an eclipse. The
orbits Of the planets are not plane;
therefore they cannot be accurately
represented on a fat service. A good
idea Of their relation may be obtained
from placing two hoops, one within
the other, so as to form slight angles
II will be seen that they cross each
other twice.
Apply this to astronomy and the two
opposite places in the orbits of planet:
where the intersection occurs are called
modes" 1t is obvious that planets
will be in q line with tho u only al
these nodes, consequently a transit can
occur nowhere else. The nodes of the
earth and Venus happen in June and
December. Two things are necessary
TO a transit-both planets must be at q
node at the same time and a line pass.
ing through both planets must strike
some portions Of the suns disc.
The last transit of Venus occurred
in 1874. AS Venus is nearer the sun
she performs her annual revolution
sooner than the earth. In order
therefore, that circumstances favor
able 70 another transit may prevail q
period Of time equal to the common
multiple Of their annual revolutions
must elapse. By the following formula
it will be seen that the required time
is about eight of our years:
Days in Annual rev. Both will be a
each year. Olutions. same node In
Earth 265X KS 1921 ~
Venus 22l7'lO xi3 9ei.1 Day
In eight years, then, from 1874 an
other transit will occur-December
1882. But the products obtained By
the above rule show a difference O.
nine-tenths of a day, which being in.
creased constantly will postpone I
recurrence Of the same phenomenon il
the same node. Two hundred anC
thirty FIVE years are required to recon
cile the difference, and a December
transit can occur until A. d. 2l17. Al
before mentioned there are two nodes
The last June transit took place il
1863; this date, plus 235 years, gives
June, 2004-a too distant period To-
any now living to consider. The as
tronomers Of this decade may thanh
their lucky stars for the rare opportu
nifty they enjoy.