The Republican. [volume] (Oakland, Md.) 1877-current, 1894-08-23
THE TIME OF MOONRISE.
1t Is Fifty One Minutes Later on Any Day
Than on the Day Before

| ahah Oh the lJly BEFORE.
The time of moonrise on any day is
on the average about fifty-one minutes
later than on the preceding day. This
retardation is. however, by no means
constant in amount, being at times
very much less than the average and
| at times very much greater. y very
marked diminution in the time of re-
| tardati0n occurs about the time of the
| full moon which falls in September.
| This moon is called the harvest moon.
| The same phenomenon in less degree
occurs at the time OF the next follow
| ing full moon, which is known as the
hunters moon. The time of retarda-
ton during the harvest moon is less
than half an hour in our ATTITUDES, in
instead of its average value of nearly
an hour. and for several successive
nights the moon seems to rise at nearly
| the same time.
Briefly stated. the cause of the phe-
nomenon is this: At the time of the
rising of the harvest moon the APP
parent path of the moon among the
zon than it is at other times, and the
ordinary days motion of the moon
| along this path makes an unusually
lkmall change of the position of the
/ Iaoon with reference to its distance
! from the horizon.
A more detailed explanation may
! make the matter little more easily
understood. In addition to the orGi-
nary apparent daily motion which the
moon has in common with all other
/ heavenly bodies. it has another motion
| by which it completes the circuit of the
| heavens relatively to the sun once u
month. and the direction of this mo-
| ton is generally not parallel with the
| direction of the diurnal motion, it be-
| ing generally northward or southwark
as well as eastward. Anyone may see
| this motion by an hours watching OF
the relative positions of the moon and
| star near it, The diurnal motion is al
ways on Il line at right angles to a line
! drawn from the body to the celestial
| pole, the point in the heavens approx
imately indicated by the pole star. 1t
| is always perfectly uniform about the
| pole as Il center. and it 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 at sunset
! the moon will still be below the hori-
! zon. because it has moved eastward
among the stars relatively to the sun,
| and it will not rise until the diurnal
| motion of the heavens brings it above
| the horizon If the moons motion
were uniform and always along the
line OF ordinary durnal motion,
this retardiation of the time
of rising would always be the
same. and would. as stated at
the outset. be ffty-one minutes per
day. But at the time of harvest moon
the direction of motion of the moon
among the stars is considerably north
ward as well as eastward. and at the
time of moonrise this line makes a com
paratively small angle with the hori-
zon very much less than it does at
other times of full moon during the
year. Therefore, at sunset on the day
after the full. the moon having moved
along a line which is inclined to the
horizon at much smaller angle than
usual, its distance below the horizon
will be less than the average. and
hence a smaller amount of diurnal mo-
ton will bring it into view-that is,
the retardation of time of rising is less
than it is at other times, This condi-
ton continues for several DAYS
Several other things, notably the in
clinatiOn of the moons orbit to that of
the earth, and the varying rate of mo-
ton in the orbit due to variation of dis
tance 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 peculiar phe-
nomenon of harvest moon. Latitude
has strong effect, and in northern
Europe the phenomenon is a much
more noticeable one than it is in the
United States In fact if one goes far
enough north, the harvest moon may
rise even earlier on any night than it
did on the night preceding.-N. Y. sun.