The Emporia news. [volume] (Emporia, Kan.) 1859-1881, 1870-03-25
ABOUT THE SUN.

AhC III 81 lAAlS W w lHIOEueE 70 drFiVc 4
at a knowledge of the size of the sun
is to. determine its distance from our
planet. Now the best way to ascertain |
the distance of any inaccessible object |
is to measure what is called base line, |
from the extremities of which the OBJ |
and then to measure with the proper
instruments the angles formed by the
distant object and the ends of the base.
For example, suppose we are standing
on the bank of an impossible river and
desire to ascertain the distance from us
of an owl perched on tree standing
on the opposite bank, we would first
measure along the bank upon which we
stand line of a certain length from the
two ends of which the bird could be
seen at one and the same moment, and
then measure the angles formed by the
imaginary line between the owl and
the extremities of our base, when we
shall have a triangle, the unknown
parts of which are readily determined
by an easy problem in Trigonometry,
Now when it Is desired TO ascertain
the distance of on object so far removed
as the sun, it is necessary to measure
very long base line, otherwise too great
a disproportion will exist between it
and the sides of our triangle. Now
there are two astronomical Observable
ries, situate in about the same longitude,
one in Hammerfest, in Norway, in the
northern, and the other at the Cape of
Good Hope, in the southern hemis-
phere. The distance between these two
places is nearly 600 miles, and being
upon the same meridian, or nearly so,
the moon or sun attains its greatest alt
itude above the horizon of each at about
the same moment. Now suppose the
sun be observed from these two places
just as it is passing their meridian, and
we have the same sort of a problem as
before. We have triangle of which
the distance in straight line between
the two observatories forms the base,
and of which the distances in straight
| lines between the sun and the extremi-
ties of our base line form the sides, and
we have the angles at the base. This
forms a triangle in which these three
things are given: the base and the two
angles at the base and we go to work
to find the other two sides of the TRAN
gle in precisely the same manner as be-
fore. In order to avoid inaccuracies
the utmost care and nicely of measure
ment are required. In fact it is almost
impossible to acquire eXactness where
so great a disproportion exists between
the base and sides of the triangle; for
the least mistake in measuring the base
line, or the base angles, or in placing
the telescope in the wrong position, that
is, removed even in the least from the
extremities, seriously affects the results
of computation. But, happily, another
method exists far more refined in prin-
ciple, whereby the suns distance can be
measured to a great degree of accuracy
1t consists in making. observations Of
the planet Venus while it is crossing
the SIMS disc, called the transit of We.
nus. Venus in her passage around the
sun comes between the earth and that
orb at intervals, alternating between
eight years and upwards of a century
1t is only on these rare occasions that
Venus is at the same time both in clos
est proximity to the earth and visible
from the two extremities of diametel
l of our planet. The distance between
! the two planets at this time is abou
one-fourth the distance of the eartl
from the sun, SO that the angular dis
placement of Venus is four times as grea
L as that of the sun. During its passag
the planet is seen projected on the sun
disc as dark spot, and the whole OBJ
servation is reduced to ascertaining tn
precise time which it requires for thu
foremost and hindmost parts of tn
planet to pass across the circular outlin
= or ring of the sun, leaving the angula
y displacement of the planet as seen froI
different points of observation for fu
= ture consultation.
= Having given the distance of the SUI
and its apparent size, measured by YER
finely constructed instruments Gale,
ie micrometers, the real diameter of tn
;, sun is easily arrived at and found t
be in round Numbers $4,000 mile!
With the real diameter given it is cas-
to find the circumference.
--------1r . -oI----