The Columbia herald. [volume] (Columbia, Tenn.) 1850-1873, 1869-08-06
ECLIPSES.

ECLIPSES.
By T. II. STAFFORD, (DIREcToR OF THE
DEARBORN OBSERVATORY, cHICAGo).
FROM time to time it is noticed that the
sun and moon are partially or totally
eclipsed; that is to say, in the suns case,
portion or the who.e of that luminary,
as we usually see it, is hidden by round,
dark body, now well known to be the
moon and in case the moon is eclipsed,
dark shadow appears to cross its disc.
We know by observation that when the
moon is eclipsed it is always full moon
that the earth is irterposed between the
sun ard the moon, aud that it is the earth's
shadow which produces the eclipse. Again,
when the sun is eclipsed it is always new
moon; and We always see the slight lunar
crescent called the new moon day or two
afterwards
But not at every full or new moon does
an eclipse take place only at certain
seasons of this kind, when the sun, earth
and moon are unusually near the same
right line for if the SIN and moon be ap-
psreutly in conjunction, that is, in the
same region of the Heavens, but at the
same time one appears so far above the
other that they escape appearing to touch,
there will be no eclipse. And in the same
way, if the moon at Its full does not pass
exactly through the earth's shadow, it may
psss over or under ii, and 80 escape an
eclipse entirely.
Before going any further, it may be well
to state that o-called total eclipse of the
moon does not cause the moon to dissp-
pear entirely but that even then she still
shines with dusky light. More Of this
further on.
There are three kinds of eclipses of the
sun-partial, the commonest kind total,
the narest; and q third kind, annulsr,
neither partial nor total, strictly speaking
The reason Of this third kind we must
think about for moment.
We all know very well that the sun and
moon appear to US very much of the same
size: but they are very different in mag
nitude. The sun is much larger, and
about as much further off; so that, as q
pane of glass in my room appears nearly
as large as q great building at half. mile
distance, 30 the sun and moon appear rela-
lively of the same size. But if 60 nearer
the window, / shall zee the pane larger
proportionably than the building and oics
0ersa If go away from the window. If,
then, we place the moon at such dis
tance from Us, and in such place, that il
will appear just to cover the whole sun,
and ther approach nearer, the moon will
appear to grow larger faster than the sun
does, and total eclipse will take place
Oh the other hand, if We go further from
the moon, it will grow Ito us) smaller, and
will not cover tie whole sun, but leave 8
ring of light outside. And just the same
thing happens in nature, when the centres
of the sun and moon appear just in the
same place to us that is, when the eclipse
is central" as ASTRONOMERS cau it. The
moon is in this case sometimes so near as
entirely to cover the sun, sometimes so far
as to leave a ring of light around itself /;
the eclipse in the first case Is called total,
in the second case annular or, as the Ger
mans say. ringformed.
When do the eclipses of the sun ia ke
place! that is, how can We predict them ?
To do this thoroughly and with extreme
accuracy, requires the tables of the suns
and moons motions, and great deal of
calculation. Large volumes are devoted
to the purpose Of telling exactly at what
point in the heavens the sun and moon
will be at any future instant, and do so
with such accuracy that We can not for
many years fail by one minute of time in
predicting when any eclipse will take
place and when even this degree of &C
curacy is reached, corrections will be made
from the results of the daily and nightly
observations now making in all civilized
countries. But it is comparatively easy to
predict when an eclipse will take place
with some approximation to the truth
and by two considerations:
First, there are two days in every yeal
| s,1 f,,1I so Hnlxy fr
bring an eclipse. For this year, thes.
dates are February 9Th snd July Both; and
SO we find by the more refined calculation
that there are eclipses Of the moon or
January 9th and July 23l, both these
dates being full moons; and of the sur
February 11th and August 7th, both these
dates being new moons.
Again, every ECLIPSE is followed by 6
somewhat similar eclipse-visible, how
ever, in a very different part Of the earth
at An interval of eighteen years, ter
days and q fraction so that the eclipse
which took place in the forenoon of july
2Sth, 1851, will be followed by one in tn,
afternoon of August 7th, 1869. But thii
eclipse of 1851 was only partial in th,
United States, and total in a small part o
North America, and through 3 small belt o
country in Europe; that of 1869 will b
total only in Q narrow belt in NortherT
Asia and North America belt which
passes through Illinois, as will be men
toned by-and-by.
Between these two eclipses, July, 1851
and August, 1859, there have been OBJ
. served about seventy others and it i
calculated that of these seventy, forty ont
have been of the sun and twenty nine o
the moon and each one of them, excep
perhaps some of the SMALLER ones, vii
have its corresponding eclipse in abou
eighteen years and ten days after its owl
! date.
Some one will here say that eclipses o
the moon are not rarer than those of tn
sun; but, on the contrary, much com
moner. On looking one moment at tn
subject, we see the fallacy of this
Eclipses of the moon can be seen every
where in that half of the earth for whicl
: the moon is up at the time of the occur
renee, but eclipses of the sun are only visi
BILE through smaller space of country. Th
great eclipse of this year has its centre il
Alaska: il does not extend much south o
the equator, nor 8 great way into Asia j
is in some degree visible over the who'll
of North America, and little way int
J the Atlantic Ocean and covers about one
fifth of the earth's surface with the va
rious boundary lines of its visibility.
And when we come to look at tn
extent of total eclipse, we see that it ex
tends over q belt of country about on
hundred and sixty miles wide, beginnin,
In Siberia, thence passing through Alaska
some of the late Hudson's Bay territories
part of Dscotah, most of Iowa, a lsrg
part OF Illinois, Indiana and Kentucky
| part OF Tennessee, most of North Carolina
and little of Northern Nebraska, Min
nesota, South Carolina and Virginia. Thi
belt Of totality just escapes the following
. important PLACES: Chicago, ST. Louis, Cfh
cinnsti, Indianapolis and Omaha; and an,
one will find that a belt one hundred anC
sixty miles wide, passing between Chicago
and St. Louis, and avoiding Omaha on til,
south and Cincinnati on the north. mus
pass about in the direction above indicated
by the States mentioned above. And yor
can represent, In rough way, the cours,
! of the shadow-thst is, of the total portion
of the eclipse-by cutting out a slip O
! paper of the width of the representative
| of one hundred and sixty miles ON AMI
!, map of the United States, and long enough
9 to reach from the map position of Beau
} fort, N c., TO that of Fort Union, Dacotah
Place this strip so that the centre of on,
r end shall be near Cape Lookout, and tn,
D edge shall Just lap over Rock Island ant
avoid Omaha. The path of the eclipse