Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematicsFerguson, James
Science
Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematics
Ferguson, James
Astronomy -- Early works to 1800
285. The farther that any place is from the Equator, if it be not beyond
the Polar Circle, the Angle gradually diminishes which the Ecliptic and
Horizon make when Pisces and Aries rise; and therefore when the Moon is
in these Signs she rises with a nearly proportionable difference later
every day than on the former; and is for that reason the more remarkable
about the Full, until we come to the Polar Circles, or 66 degrees from
the Equator; in which Latitude the Ecliptic and Horizon become
coincident, every day for a moment, at the same sidereal hour (or 3
minutes 56 seconds sooner every day than the former) and the very next
moment one half of the Ecliptic containing Capricorn, Aquarius, Pisces,
Aries, Taurus, and Gemini rises, and the opposite half sets. Therefore,
whilst the Moon is going from the beginning of Capricorn to the
beginning of Cancer, which is almost 14 days, she rises at the same
sidereal hour; and in autumn just at Sun-set, because all that half of
the Ecliptic in which the Sun is at that time sets at the same sidereal
hour, and the opposite half rises: that is, 3 minutes 56 seconds, of
mean solar time, sooner every day than on the day before. So whilst the
Moon is going from Capricorn to Cancer she rises earlier every day than
on the preceding; contrary to what she does at all places between the
polar Circles. But during the above fourteen days, the Moon is 24
sidereal hours later in setting; for the six Signs which rise all at
once on the eastern side of the Horizon are 24 hours in setting on the
western side of it: as any one may see by making chalk-marks at the
beginning of Capricorn and of Cancer, and then, having elevated the Pole
66-1/2 degrees, turn the Globe slowly round it’s Axis, and observe the
rising and setting of the Ecliptic. As the beginning of Aries is equally
distant from the beginning of Cancer and of Capricorn, it is in the
middle of that half of the Ecliptic which rises all at once. And when
the Sun is at the beginning of Libra, he is in the middle of the other
half. Therefore, when the Sun is in Libra and the Moon in Capricorn, the
Moon is a Quarter of a Circle before the Sun; opposite to him, and
consequently full in Aries, and a Quarter of a Circle behind him when in
Cancer. But when Libra rises Aries sets, and all that half of the
Ecliptic of which Aries is the middle. And therefore, at that time of
the year the Moon rises at Sun-set from her first to her third Quarter.
[Sidenote: The Harvest Moons regular on both sides of the Equator.]
286. In northern Latitudes, the autumnal Full Moons are in Pisces and
Aries; and the vernal Full Moons in Virgo and Libra: in southern
Latitudes just the reverse because the seasons are contrary. But Virgo
and Libra rise at as small Angles with the Horizon in southern Latitudes
as Pisces and Aries do in the northern; and therefore the Harvest Moons
are just as regular on one side of the Equator as on the other.
Public-domain text, read in full here on John Shaqi.
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