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The har. vest and

Moon,

Moon's

hand than the Moon does with regard to the Sun.

282. As the Moon can never be full but when she hunter's is opposite to the Sun, and the Sun is never in Vir- .

go and Libra, but in our autumnal months, it is plain that the Moon is never full in the opposite signs, Pisces and Aries, but in these two months. And therefore we can have only two full Moons in the year, which rise so near the time of sun-set for a week together, as above-mentioned. The former of these is called the Harvest Moon, and the latter

the Hunter's Moon. Why the

283. Here it will probably be asked, why we neregular ri. ver observe this remarkable rising of the Moon but sing is ne- in harvest, seeing she is in Pisces and Aries twelve ver permut times in the year besides; and must then rise with in harvest. as little difference of time as in harvest? The answer

is plain : for in winter these signs rise at noon; and
being then only a quarter of a circle distant from
the Sun, the Moon in them is in her first quarter :
but when the Sun is above the horizon, the Moon's
rising is neither regarded nor perceived. In spring
these signs rise with the Sun, because he is then in
them; and as the Moon changes in them at that
time of the year, she is quite invisible.
mer they rise about midnight, and the Sun being
then three signs, or a quarter of a circle before
them, the Moon is in them about her third quarter;
and when rising so late, and giving but very lit-
tle light, her rising passes unobserved. And in
autumn these signs, being opposite to the Sun,
rise when he sets, with the Moon in opposition,
or at the full, which makes her rising very conspi,
cuous.

284. At the equator, the north and south poles lie in the horizon, and therefore the ecliptic makes the same angle southward with the horizon, when Aries rises, as it does northward when Libra rises, Consequently as the Moon at all the fore-mentioned patches rises and sets nearly at equal angles with the horizon

In sum

all the year round, and about 50 minutes later every day or night than on the preceding, there can be no particular harvest-moon at the equator.

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, while 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 the 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 while 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 si. dereal 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 662 degrees, turn the globe slowly round its axis, and observe the rising and setting of the ecliptic. As the beginning of Aries

vestmoons re

of the

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 hehind him, when in Cancer. But when Li. bra 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. The har. 286. In northern latitudes, the autumnal full

Moons are in Pisces and Aries; and the vernal full gular on Moons in Virgo and Libra: in southerŋ latitudes, both sides

just the reverse, because the seasons are contrary, equator. 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.

287. As these signs, which rise with the least angles, set with the greatest, the vernal full Moons differ as much in their times of rising every night, as the autumnal full Moons differ in their times of setting; and set with as little difference as the autumnal full Moons rise: the one being in all cases the reverse of the other.

288. Hitherto, for the sake of plainness, we have supposed the Moon to move in the ecliptic, from which the Sun never deviates. But the orbit in which the Moon really moves is different from the ecliptic: one half being elevated 5} degrees above it, and the other half as much depressed below it. The Moon's orbit therefore intersects the ecliptic in two points diametrically opposite to each other; and these intersections are called the Moon's nodes. So the Moon can never be in the ecliptic

but when she is in either of her nodes, which is at The

Moon's least twice in every course from change to change, nodes and sometimes thrice.' For, as the Moon goes almost a whole sign more than round her orbit from change to change; if she passes by either node about the time of change, she will pass by the other in about fourteen days after, and come round to the former node two days again before the next change. That node from which the Moon begins to ascend northward, or above the ecliptic, in northern latitudes, is called the ascending node; and the other the descending node; because the Moon, when she passes by it, descends below the ecliptic southward.

289. The Moon's oblique motion with regard to the ecliptic causes some difference in the times of her rising and setting from what is already mentioned. For when she is northward of the ecliptic, she rises sooner and sets later than if she moyed in the ecliptic; and when she is southward of the ecliptic, she rises later and sets sooner. This difference is variable even in the same signs, because the nodes shift backward about 19 degrees in the ecliptic every year; and so go round it contrary to the order of signs in 18 years 225 days.

290. When the ascending node is in Aries, the southern half of the Moon's orbit makes an angle of 5 degrees less with the horizon than the ecliptic does, when Aries rises in northern latitudes: for which reason the Moon rises with less difference of time while she is in Pisces and Aries, than she would do if she kept in the ecliptic. But in years and 112 days afterward, the descending node comes to Aries; and then the Moon's orbit makes an angle 5 degrees greater with the horizon when Aries rises, than the ecliptic does at that time; which causes the Moon to rise with greater differ. ence of time in Pisces and Aries than if she moved in the ecliptic.

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291. To be a little more particular, when the ascending node is in Aries, the angle is only de. grees on the parallel of London when Aries rises. But when the descending node comes to Aries, the angle is 20 degrees; this occasions as great a difference of the Moon's rising in the same signs eve. ry nine years, as there would be on two parallels 10 degrees from one another, if the Moon's course were in the ecliptic. The following table shews how much the obliquity of the Moon's orbit affects her rising and setting on the parallel of London, from the 12th to the 18th day of her age; supposing her to be full at the autumnal equinox : and then, either in the ascending node, highest part of her orbit, descending node, or lowest part of her orbit. M signifies morning, A afternoon : and the line at the foot of the table shews a week's difference in rising and setting.

|Full in her Aseend. In the highest pt.jFull in her Descend- In the lowest pt. of ing Node. of her Orbit.

ing Node.

her Orbit.

Moon's Age.

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135

12 15 A 15! 3 M20 4 A 30 3M15 4 A 32 3M405 A 16 3M 0

324 2514 50 4 4515 15/ 4 2016 ol 4 15 14 5 48 5 305 15) 6 015 45 5 406 2015 28 15 16

5 7. 015 421 7 2016 15! 6 5616 45 6 32 16 6 2018 15.6 2 8 3516 46 8 07 817 45

36 9 126 26! 9 4517 189117 301 9 15 18 16 5410 S017 0 10 4018

0/10 2017 5210 0

17 16

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This table was not computed, but only estimated as near as could be done from a common globe, on which the Moon's orbit was delineated with a blacklead pencil. It may at first sight appear erroneous ; since as we have supposed the Moon to be full in either node at the autumnal equinox, ought by the

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