New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1884-11-08
A DARK LUNAR ECLIPSE.
nv RICHARD A. PROCTOR.


ur,,s STRANGE MlsTAKE-IRRrGULAR 1lLC-
,ux.r,oy OF TIE MooN-MIsrAKEs on THE
sra,rcr-RrssrIL's IMAGISED LUNAR AuRoRAs
rrAI rXpIANATION-OpD MISTAKE OF THE
LONDON TIMES-sUNRIsE AND SUNSET pofu>"
THE ECIIPsE-JULEs vERNf's IDEAL ECLIPSE of
sun By THE EARTH.
The total eclipse If the moon on October ath' VS.
ible in Europe. was unlike most lunar echpseS III
Heed unlike all which have been observed curing
ebnnt hundred years. Usually. as most persons
know, the moon shines with strong iuu-
DIV or coppcry tint, even when she
il totally immersed IN he earths shadow. III
deed this ruddylight appears stronger when she IL
Totally immersed than when she is only partially
I'm he shadow though this OF course. is only an OPP
tcol illusion. the relative darkness of the
shadowcd portion when she is partially ecllpsed
being due to contrast with the bright uneclipsed
por ion In ndeclipsc the moons disc sometimes
looks so bright that astronomers have been charged
with errors Of computation by ill-nformcd persons.
who have imagined that the moon has not been
eclipsed ~ all.
On October T. however. the case was otherwise.
My friend the ariing editor of hnoriefge, an as-
jrnunpr Of great skill, who has observed many
pclipsns Of the moon. writes that the elect al the
,ime Of ict tliiy differed from any which he hau
rtrvinnsiv witnessed. Ordinarily at the time 81
greatest uhsrutntbnn the moon has assnmeh the
appearance NJ glowing currrtv-trd hall, TN SAT-
niiat shr was barely Visible "a ~ ill-'lriiheh rue
If a schi, airen hue" me iim'ss account OF the
eclipse, apparently written ht one ~ the oii'a'
ssty momr,s AZ Greenwich, states that Tic mosl
striking features az the eclipse we're The exceedingly
darn ooor 1T tho eoiipsot moon, ahd-hei"fe ana
sfter toiality-the distinct edge of the shadow ANA
mort ION of the moon contiguous 10 IT," tlhe writer
OF the description means here the definite contrast
be- ween the pat IN shallow aud The rest OF tue
moons facet Instead OF The usual ooppery red
ness tho appearance was at times rainier very
dark brown or almost black, so much 80 that per
sons who have observed many lpses agree III con-
siderlng tins the darkest they had ever seem"
propose to make tins cepional lunar eclipse the
text for some remarks on the phenomena of lunar
tcipses generally, about winch singniarly large
number of mistakes have been made even by we'll
Informed astronomers.
Kepler was the first who explained the true
reason why the moon does not ordinarily dis
appear in the earth's shadow, even when deeply
Immersed therein. He showed that the atmosphere
Of our earth, which has rcractve power sufficient
TO raise the whole disc of the sun into view when
he has set geometricaly, that is when lie Is wholly
be ow the plane of the horizon must be able to bend
the suns rays as to fall upon the moon, even
when the moon is totally immersed in what may be
called the geometrica shadow of the EARTH that u.s.
the region which would be III shadow If the suns
rays were not thus detected The ruddy color Of
the moon at this time is of coarse due TO the same
cause which produces the muddy color of the setting
SUM- VIZ: the ahsorptive action of the lower and
more moisture laden LAYERS of our own atmosphere.
II was in regard to this perfectly sound explaua-
ticn that the rst and one of the strangest mistakes
about lunar cclipses made by one of the great
est astronomers the world has known. Sir William
Herschel reasoned that Kepler's EXPLANATION could
not be valid, for the bending power of the ar
only defects the suns rays even when
he is on the horizon. bv about half degree lin re-
ahty nearly thrty-ive minutes Of arc) while the
globe OF the EARTH seen from the moon, has an
apparent breadth Of about two degrees. There
was treble mistake here, such as few even of the
greatest men Of science have accomplished
outstanding Leibic's paradox that the man who
has made no mistakes has achieved nothing great.
For first when the sun is just behind the earth's
centre to a supposed lunar observer tine rays from
thelnldie Of his disc have only to he bent degree.
seeing that he sun is out Of by the span of NE
c01ths radius, MT by the span of her diameter.
Secondly, the sun Is not point, but as seen from
lie mo0l, has an apparen, span Oi about half de
grcc o. a fourth % the apparent diameter of the
sartn so that bending power Ol on three iOurths
that iu.t mentioned woul suffice to bring him into
,he prolongaton OF the line from the moons
rentIe to the cath's. But, thirdly, and this
was the worst part of the mistake, Sir William
Uerschel considered only half the bending power OF
tie earth's atmosphere. When we see tie setting
sun lifted above the horizon by reraciDn. the rays
which come to us horizontally from the sun have
really been bent through an angle OF about 30 min
ntes as they entered the air and passed 20 the Oh
server; the same rays going on would hc bent
through another anpc If the same amount rs they
passed ou then way ont thus the total detection
Of sun rays which just gtaze the earth's surface
and pass onward. Il 30 minutes Of are by
Tho time they have completed Their VA sage.
A. only about - minutes DETECTION is required
To- ifina some part Of the surs di7c into view, even
when he ia centrally bohind tho earth. and only
shult anvanty-hve minutes tp bring him wholly
jata Wow. IL "a evident that Whph he ia thus siiu
eied must ut hiA hight ia brought ut" view round
pvrfy pat 81 the outline 81 the eatil'H disc, lio-
,drd tho ali "a etcf, Vhoip con oYef chat spne nl
Tho earth which AZ ihr mumeht fnima hofuutlinr 40
teru rom the moon,
kepei's Aplanaiinn vas correct tlirn, ahd sn soon
D. tho iallicy underlying bir ", ilelaenel so'leo-
ton had been pointed out that exp ahalioh ir-
fumed is pc, ton asa valid aud sufficient inini-
petatlon OF the moun'a Paddy hight DUNG her total
H. mcIsion ia tLc ooItl's shadow.
But il has been used for the explanation If pc
cuarity with which, n reality, II has little to do,
viz; Irregular diyersltics in the Illumination OF
the moon > disc hay, just spoken OF the clear
ness Of the earths anos pLcIe where 1t las To act
10 bend the sans RAYS toward the moon. OF course
thestaic OF tho ar Ia this respect is variable aud
in different part. OF the zone over which the bend
ing takes place different conditions must III most
cases prevail over some parts of the zone the air
may be so cloud-la0en that no light at all he
detected to the moon. for the retractive power of
the ar above cloud layers extending to any consid-
erable height above the earth would rot suffice to
produce tie necessary detection. Thus different
part OF the great atmosphere zone at work in de-
Nccflnn he snn's ravs TO the moon dnTlng tOial