The Helena independent. [volume] (Helena, Mont.) 1875-1943, 1894-01-09
nAnvEsr 40 AuNTGR.s MooNs.


H~icf Statements a. 60 che Causes % These
Celestial Phenomena.
Tho tiino of moonriso on any day o. on
the averaeo about Oh minutes later than
10 was on the preceding day. This rotaria-
tinn D.. however hy uo means constant in
amount. being go times very much less
than the average and at times very much
greater A very marked diminution IN
the time of retariation occurs about the
tno of the fun moon which falls Ia Sep
temher This moon Is called the harvest
moon. The Same phenomenon In a less
dcrroe occurs at the lme Of tho next fol-
lowing FUN moon, which Il known a. the
hunters MOON The time of rctardation
during the harvest moon Is less than half
nu hour in oar ATTITUDES, instead az its av-
eraee value Of nearly am hour. and for sew
eral successive nights the moon seems 20
rise at nearly the same time.
Briefly stated. the cause Of the phenom-
onon Is this. 40 the time Of the rising Of
the harvest moon the apparent path Of
the moon among the stars Is much less in
olincd 90 the horizon than it Is at other
times. and the ordinary days motion 81
the moon along this path makes an UNI
usually small change Of position Of the
moon with reference 20 il distance from
the horizon.
4 more detailed explanation may make
the matter little more easily understood.
In addition to the ordinary apparent daily
motion which the moon has in common
with AIN other heavenly bodies, 10 has
another motion by which il completes the
circuit Of the heavens relatively 20 the sun
once month. and the direction of this
motion Is generally not parallel with the
direction eff the diurual motion, IL being
generally uorthwurd or southwark as well
as eastward. ANY one may see this mo-
tion by an hours watching Of the relative
positions of the moon and star near 1t.
The diurnal motion is always on line at
right angles to "a line drawn from the body
10 the celestial pole the point In the heav-
ems approximately indicated 10y the pole
star IL is always perfectly uniform about
the polo as a center, and IL Is this which
we take as our ordinary measure Of time.
Now consider the position Of the moon
and the sun at the time Of full moon. The
moon rises just as the sun sets. On the
next evening 40 sunset the moon will still
he below the horizon, because IL has moved
eastward among thes stars relatively 20 the
sun. and it will not rise until the diurnal
motion OF the heavens brings il above the
horizon Ii the moon motion were I'M
form and always along the line Of ordi-
nary diurnal motion, this retardation Of
the time of rising would always be the
same, and would, as stated at the outset,
be 81 minutes per day But at the time
Of harvest moon the direction of motion Of
the moon among the stars is considerably
northward as weil as eastward. and at the
time OF moonrise this line makes a com
paratively small angle with the horizon,
very much less than 90 does at other times
Of full moon during the year. Therefore,
az sunset on the day after the full, the
moon having moved along a line which Is
inclined 90 the horizon at a much smaller
angle than usual, its distance below the
horizon viii be less than the average, and
hence "a smaller amount of diurnal motion
viii bring 10 into view-that is, the retar-
dation Of time Of rising is less than it is
at other times. This condition continues
for several days.
Several other things, notably the inoli-
nation of the moons orbit 10 that Of the
earth. and the varying rate of motion ia
the orbit due 20 variation Of distance from
the earth. tend to change the amount Of
daily retardation, but they do not depend
ON the time of the year, and they sometimes
intensity and sometimes diminish the pc
culiar phenomenon Of harvest moon, Lat
itude has a strong effect, and in northern
Europe the phenomenon Is a much more
noticeable one than it Is in the United
States. I'm feet. If one goes far enough
north. the harvest moon may rise even ear
lier ON amy night than it did on the night
preceding Popular Science Monthly.