The Portland daily press. [volume] (Portland, Me.) 1862-1921, 1893-11-17
The Harvest and Hunters Moon.

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The time of moonrise on any day is on
the average about 81 minutes later than
it was on the preceding day. This re-
tardation is, however, by no means con-
slant in amount, being at times very
much less than the average, and at times
very much greater. A very marked di-
intuition in the time of retardation oc-
ours about the time of the full moon.
which falls in September. This moon is
called the harvest moon. The same
phenomenon in a less degree occurs at
the time of the next following full moon,
which is known as the hunters moon.
The time of retardation during the har-
vest moon is less than half an hour
in our la titudes, instead of it's 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 apparent path
of the moon among the stars is much less
inclined to the horizon thaait is at other
times, and the ordinary days; motion of
the moon along this path makes an
unusually small change of position of
the moon with reference TO its distance
from the horizon.
A more detailed explanation may make
the matter a little more easily under
stood. In addition to the ordinary appar-
ent daily motion which the moon has in
common with all other heavenly bodies,
it has another motion by which it COM
pietes the circuit Of the heavens relative
1xrf Eha
direction OF this motion is generally
not parallel with the direction OF the
diurnal motion, it being generally north
ward or southwark as we'll 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 always on a line at
right anlges to line drawn from the
body to the celestial pole, the point in
the heavens approximately indicated by
the pole star. 1t is always perfectly IN
form about the pole as 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 the full
moon. The moon rises lust as the sun
sets. In the next evening at sunset the
moon will still he below the horizon,
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.
Ii the moons motion were uniform and
always along the line Of ordinary 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
nothward as well as eastward, and at the
time of moonrlse this line makes COM
paratively small angle with the horizon,
very much less than it does st other
times of full moon during the year.
Therefore at sunset on the day after the
full, the moon having moved along
line which is inclined to the horizon at
much smaller angle than usual, it's
distance below the horizon will be less
than the average, and hence smaller
amount of diurnal motion win bring it
into view-that is, the retardation of time
of rising is less than it is at other
times. This condition 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 motion
in the orbit due to 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 peculiar phenomenon of
harvest MOON Latitude has strong
effect, and in northern Europe the phe.