The Albany register. [volume] (Albany, Or.) 1868-18??, 1874-11-27
FIGURE I.

be i'll inferior conjunction. When 1t IS
on the opposite side of the sun from the
earth it is in superior conjunction.
Thus, in fig. 1, suppose F represents
the orbit of the earth,.A that OF
Venus. and the sun. If Venus is at
when the earth is at e, it is in inferior
conjunction But the orbit of Venus,
as you see by the figure, is not in the
same plane with that of the earth.
Now, if it were extended until it met
the earth's orbit, it would be repre-
sented by the dotted line E, and it
would cross the earth's orbit at the
points and G. These points, or the
corresponding places and v, in the
real orbit of Venus, are called its nodes.
Now, because of this inclination of the
two orbits, the sun, Venus and the
earth will be in the same line only when
Venus is at, or near, one of its nodes at
the time of conf junction. For, if Venus
is at F when the earth is at F, it would
be in inferior conjunction, because it is
in that part of it's orbit which is most
directly between the earth and sun but
we should see it in the direction of c.
| If, however, it is at its node, v, at the
time of conjunction, or when the earth
is at E. we see it in the same line as the
sun, and it then appears to pass directly
| across the suns disc. This is what is
opaque, like the earth, shining by the
reflected light of the sun therefore the
| bright side is toward the sun, and at
/ the time of transit it appears to us
| like dark spot upon the suns bright
surface.
The transits of Venus happen only at
rare intervals, because it is seldom that
| the three bodies are thus situated in
reference to each other. They occur in
pairs, eight years apart, and between
the pairs are one hundred and five, or
else one hundred and twenty-five years.
The fact that they SO rarely happen
occasions an interest in the transits !;
but this is by no means the only reason
why they are SO carefully watched.
Their chief Importance lies in this: By
observing the path which the planet
makes across the sun we obtain data
from which the distance of the earth
from the sun can be calculated. The
Tel0tiUe distances of all the planets
from the sun is known; therefore, when
the earth's distance, expressed in miles,
is obtained, we have, as it were, yard
stick by which the distances of the
other planets can be measured. To find
the ecact length of this yard stick has
long been considered the astronomers s
grandest problem, and transit of
/ Venus gives the most accurate means of
doing this.
The last two transits were in 1851 and
1869. Previous to these the estimates
which had been made of the suns dis
tance from the earth were very incor-
rect. The earliest estimates on record
made it about one-twentieth of it's true
distance and even at the time of these
transits it was too small by several
million miles. These transits were,
however, watched with great interest,
the observations made of them carefully
compared, and the distance computed
to be about ninety-tive million miles.
Since then astronomers have calculated
the suns distance by several other
methods, applying principles which
were not then known, and, although
these methods are inferior to that fur
nished by transit, yet, as the different
calculations very nearly agree, it is
supposed they are not far from correct.
They show the suns distance to be a
little over ninety one million miles.
The instruments which we now have
for measuring small angles, and the
means for determining the latitude and
longitude of places are much superior
to those used a hundred years ago.
hence the observations of the coming
transit will be much more exact, and
will furnish q means of testing the ac-
curacy of previous calculations.
Twill now tell you something of how
the observations are taken, and of the
preparations which have been made fol
this purpose.
The direct object is to obtain what is
,, called the suns parallax. The parallaz
of an object is it's apparent displacement
as seen from two different stations. Ii
, fig. 2, let the circle represent {
. section of the earth. Two persons, ons