Nashville union and American. [volume] (Nashville, Tenn.) 1868-1875, 1874-11-22
VENUS In TRANStTU.
A Plain, Unyarnished Explanation Of
the Great Astronomical Event

the Great Astronomical Event
To the Union and American.
Scientific men are, all ever the civilized
e5rth, awake to the importance Of the OBJ
servatiOns 10 be made of the approaching
transit of Venus. The unscientifc know
but little about il, and for their inforna-
tiOn your correspondent desires TO collaie
from different sources a few items which
will doubtless lJe of service 10 the general
reader. lie claims no Originality-onlya 4
condensation OF scientific facts from those
who have written upon the subject.
The planet Venus is one of the most
brilliant in the heavens, whose orbit is be
tween that Of Mercury and that of the earth,
being second FROM the sut. u is . little
less in size than the earth, and has no sat
elite. 1t is about 6S,0O0OOO OF miles from
the sun, and reYOlves around it in about
224 days. Seen through telescope, as
tronomers tell us, Venus exhibits phases
like the moon. There will be an annular
eclipse Of the sun by this planet ON the
Sth of next month, (December,) when it
will pass across the sun for the first time
since the year 1863. The approaching
transit will not be visible in America, but
will be in Asia, Borneo, Australia, etc.
The beginning can be seen in the Sand
wich Islands, and the end in Egypt, Asia
Minor, and some other places.
The tTansits of Venus occur at the very
irregular but constantly recurring intervals
of l2I5, s, and 1868 years. So that there
will be another transit Of this planet on
the 9th Of December, 1852, eight years
hence, while the next one will be in the
year A. d. 20O4. The only possible chance,
therefore, for observations, for long years to
come, will be on the Sth Of next month,
and on the 9th of December, 1882. Exten-
sive Preparations have been made for the
proper observations Of the approaching pas
sage Of Venus across the disc Uf the sun,
and for the one to follow eight years from
now. The transit of 1882 will be visible
in our Atlantic States, the West Indies,
South America, AMI generally in the more
inhabited portions Of the globe. The va
riOus instruments now used will be kept
for use in 1882, and it is supposed that the
observations then made, will be more thor
ough, accurate and complete, than those to
be EIade little more than two weeks
hence. But the observations TO be made
this year, viii DOUBTLESS be of vast impOr-
tance to the wcrld.
,SAmOng the important reasons for these
observations, the following is the chief:
Scientific men need a correct measuring
line, or yardstick, to measure the distance
from the earth to the sun, and from one
heavenly body to another. The transit of
Venus affords the opportunity to procure
such a yard-stick better than any other
known means. This is the astronomers
grand problem, TO get an exact measuring
line.
Our calculation that the sun is ninety
five millions of miles from the earth may
be wrong, and, if so, our calculations rs to
the relative distance Of one orb from an
other are equally wrong. Hence the great
importance of a correct observation of the
approaching transit, and of the one that
will occur in 1882.
For two or three years past, the different
Governments have been making arrange
ments for the approaching observations.
The United States, England and Germany
have made more extensive arrangements
for these observations than other countries.
Our Government has appropriated one hun
dred and fifty thousand dollars for the pur-
pose, besides furnishingi ships to convey
scientific men to the places selected for
taking the observations. The stations TO
be occupied by Americans, next month, are
near Rekin, Yeddo, a point near the Cas-
plan Sea, tie Chatham Islands (east Of
New Zealand), some point in New Zealand,
Kerzealan's Land, Island of Mauritius, and
Hobart Town, in the southern part of Aus
tralia-eight in all. 1t is of the utmost
Importance that those making the Observa-
tions shall be for months beforehand at
their proper stations. testing their inStru-
mentS, etc. It is very difficult matter TO
make accurate observations. The instru-
mentS maynot be perfect in every particular,
and a small mistake in measuring an angle
at so great q distance from the sun, will
make a great difference in the result.
Watches and clocks may differ by one or
two seconds, and the state OF the atmOs-
phere will affect the distinctneSs with
which the planet is seen. As it is eX-
tremely difficult to tell the second when
the edges of Venus and the sun meet, a
serious error may occur. The dark edges
of the planet appear 10 be drawn out to-
wards the sun before ii really touches it,
and there is difference between the real
and the apparent contact. The object is TO
obtain what is called by astronomers the
suns pa-allax. The parallax of an object
is its apparent displacement, as seen from
two different stations; therefore, Obserya-
tions must be taken at different points, and
all are to be afterwards carefully compared.
Another mode Of measuring small angles
in the eayens, IS that of photographing the
object, and then making the desired meas
urement on the plate by an instrument call
| ed a micrometer. The sun has been Otter
| photographed for the purpose of studyins
| the solar spots, and with great success
Wonderful advanoements may be expected
in the science of astronomy, within tb'
next few years, by the proposed telescope
observations, and by the art autobiography
1t may not be ont of place TO add tina
only three of the transits of Venus hay
been observed, SO far rs is now known; th
first i'm Dec. 1879, by only 4 young English
man, near Liverpool; the second in JUNE
176l, and the third in June, 1769, by a:
tronomers sent expressly for the purpose
proper points, as will now be done.
a. n.