The Hawaiian gazette. [volume] (Honolulu [Oahu, Hawaii]) 1865-1918, 1874-06-24
THE RARITY OF THE EVENT.

'a1ious VI IuS approaching transit OF eQuS are
the means relied upon to accomplish this scienti-
fc feat.
THE RARITY OF THE EVENT.
Between the hours of nine o'clock of our time
on the evening of December sth, and two o'clock
on the morning of December 9th, of the present
year, trained observers from nearly every civilized
nation in the world WILL from well selected points.
be carefully scanning the passage of the planet
Venus across the luminous disc Of the sun
There has been no such phenomenon visible from
the earth since 1869, and there will not be an.
other alording equal facilities for accurate obser
vations, till the year 2OO4 Another transit will
indeed take place eight years hence; but the
suns altitude above the horizon on that occasion
will be too slight to present favorable conditions
for observation. As the period Of this years
transit occurs during the Northern Winter. the
base of observation must be established for the
most part south Of the equator. Points of OBJ.
seryatiou must be marked off in pairs, because
the entire problem depends on ascertaining with
perfect exactitude the time at which the various
stages Of the transit are observed at widely sepa-
rated stations on the earth's surface In fact,
this method Of fixing the angle of the solar par
allaX is simply working out, on colossal scale.
of the familiar geometrical process Of construct
ing two sides of a triangle in order to determine
the third. The largest attainabe base of the
presumed triangle would Of course be the eartb's
diameter-lSO degrees. But suppose two obser
yers situated at this distance apart, and to the
one the sun at the time of the transit would inst
be rising, while to the other it would be on the
point of setting. For the purposes of observa-
ton, however, the sun must not be lower in
either case, than lOo above the horizon. The
easterly observer must be so placed that the
egress OF Venus from the suns disc shall con. |
clude not too near sunset, and the corresponding
observer at the west end must be able to watch
the ingress of the planet little after sunrise.
OF course this cannot be accomplished without
contraction of base considerably within the limit
Of 1909
WHAT IS TO BE ESTABLISHED.
The length of this supposed base of the TRAN.
gle, whose apex is the sun. requires in the
first place to be determined with mathematical
accuracy. In other words it is necessary to care
July establish, by lunar observation, what is
called the absolute longitude of each station. and
50 to secure perfect correspondence of astro-
lOmical time, say within second, as basis of
between corresponding stations.
This Of itself requires some months of prepare
ion, assisted by instruments Of the utmost deli
'acy, and for the preliminary purpose several
,orps of observers are on the eve of departure
rom England to certain desolate regions Of the
Antarctic Ocean, selected as the one extremity (
# the terrestrial base for the required triangle.
)f course the conditions Of the problem are
ather more complicated than can be briefly and {
popularity indicated The relative velocities of
he earth and Venus must be taken into account;
heir relative distance from the sun enters into q
he calculation, so do questions Of atmospheric {
efraction and other delicate points which can
ardly be briefly indicated without the use of {
cientifc nomenclature. But this much can be d
aadily remembered Venus moving faster than
he earth, crosses the suns face from east to Y
est. The most easterly of two observers, b
lerefore, is the first to see the black orb of We
US completely within the outer rim Of the suns f
sc; in scientific phrase. he is situated at the v
oint Of greatest accelemton.n The companion o
Dserver at the westerly end of the line sees the
ime phenomenon some twenty minutes later n
I'd is said to be at the point of greatest retard RI
ion" Let the exact moment say of two such T,
itical points Of the transit as the ingress and
,ress of the planet on the suns disc be noted OF
ich station, and the absolute time interval be- n
Veen the observations of two stations be CON- n
lred with the distance and qualified by the a
her conditions to which we have referred. and fc
e much-soughtior angle will be nearer determi- Vi
ltion than it is to-day.
THE PREPARATIONS. Il
England France, Germany, Russia, and now b.
e United States are busily equipping astronom-
al expeditions to assist in solving what has been is
silly called zone of the sublimest problems Of al
e universe Telescopes equatorily mounted, fr
d driven by clock work, so as to remain stead RI
fixed on the sun after being once pointed at 70
photO-telegraphs of the most delicate con NJ
uction to present microscopieally accurate 70
nscrints Of evprv nhase If Tho transit. altaz; m