_The Phenomena of the Harvest-Moon explained by a common Globe: The
years in which the Harvest-Moons are least and most beneficial from
1751, to 1861. The long duration of Moon-light at the Poles in winter._
[Sidenote: No Harvest-Moon at the Equator.]
273. It is generally believed that the Moon rises about 48 minutes later
every day than on the preceding; but this is true only with regard to
places on the Equator. In places of considerable Latitude there is a
remarkable difference, especially in the harvest time; with which
Farmers were better acquainted than Astronomers till of late; and
gratefully ascribed the early rising of the Full Moon at that time of
the year to the goodness of God, not doubting that he had ordered it so
on purpose to give them an immediate supply of moon-light after sun-set
for their greater conveniency in reaping the fruits of the earth.
[Sidenote: But remarkable according to the distance of places from it.]
In this instance of the harvest-moon, as in many others discoverable by
Astronomy, the wisdom and beneficence of the Deity is conspicuous, who
really ordered the course of the Moon so, as to bestow more or less
light on all parts of the earth as their several circumstances and
seasons render it more or less serviceable. About the Equator, where
there is no variety of seasons, and the weather changes seldom, and at
stated times, Moon-light is not necessary for gathering in the produce
of the ground; and there the moon rises about 48 minutes later every day
or night than on the former. At considerable distances from the Equator,
where the weather and seasons are more uncertain, the autumnal Full
Moons rise very soon after sun-set for several evenings together. At the
polar circles, where the mild season is of very short duration, the
autumnal Full Moon rises at Sun-set from the first to the third quarter.
And at the Poles, where the Sun is for half a year absent, the winter
Full moons shine constantly without setting from the first to the third
quarter.
[Sidenote: The reason of this.]
It is soon said that all these Phenomena are owing to the different
Angles made by the Horizon and different parts of the Moon’s orbit; and
that the Moon can be full but once or twice in a year in those parts of
her orbit which rise with the least angles. But to explain this subject
intelligibly we must dwell much longer upon it.
[Sidenote: PLATE III.]
274. The [59]plane of the Equinoctial is perpendicular to the Earth’s
Axis: and therefore, as the Earth turns round its Axis, all parts of the
Equinoctial make equal Angles with the Horizon both at rising and
setting; so that equal portions of it always rise or set in equal times.
Consequently, if the Moon’s motion were equable, and in the Equinoctial,
at the rate of 12 degrees from the Sun every day, as it is in her orbit,
she would rise and set 48 minutes later every day than on the preceding:
for 12 degrees of the Equinoctial rise or set in 48 minutes of time in
all Latitudes.
[Sidenote: Fig. III.]
275. But the Moon’s motion is so nearly in the Ecliptic that we may
consider her at present as moving in it. Now the different parts of the
Ecliptic, on account of its obliquity to the Earth’s Axis, make very
different Angles with the Horizon as they rise or set. Those parts or
Signs which rise with the smallest Angles set with the greatest, and
_vice versâ_. In equal times, whenever this Angle is least, a greater
portion of the Ecliptic rises than when the Angle is larger; as may be
seen by elevating the pole of a Globe to any considerable Latitude, and
then turning it round its Axis in the Horizon. Consequently, when the
Moon is in those Signs which rise or set with the smallest Angles, she
rises or sets with the least difference of time; and with the greatest
difference in those Signs which rise or set with the greatest Angles.
[Sidenote: Fig. III.