Degrees. difference. difference. every day than she rose on the former, and differs only 28, 24, 20, 18, or 17 minutes in setting. But when she comes to Pisces and Aries, she is only 20 or 17 minutes later in rising. H. Μ. Η. Μ. 170 461 5 2 26 1 100 43 16 Aquarius, 10 401 8 3 Leo, 10 1 140 37 17 4 231 170 32 18 270 301 15 100 25 1 16 6 191 150 24 20 230 201 17 In the time that the Moon goes round the ecliptic from any conjunction or opposition, the earth goes almost a sign forward, and therefore the Sun will seem to go as far forward in that time; (namely 27+ degrees,) so that the Moon must go 27 degrees more than round, and as much farther as the Sun advances in that interval; which is 2i's degrees before she can be in conjunction with, or opposite to, the Sun again. Hence, it is evident, that there can be but one conjunction, or opposition to the Sun and Moon, in any particular part of the ecliptic in the course of a year. As the Moon can never be full but when she is opposite to the Sun, and the Sun is never in Virgo and Libra only in our autumnal months, it is plain that the Moon is never full in the opposite signs, Pisces and Aries, but in those two months. Therefore we can have only two full Moons in the year, which rise so near the time of setting for a week together, as above mentioned. The former of these is called the Harvest Moon, the latter the Hunter's Moon. 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. As these signs which rise with the least angles, set with the greatest; so the several 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. For the sake of plainness, the Moon has been supposed 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. 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. The Moon can therefore never be in the ecliplic but when she is in either of her nodes, which is at least twice in every course, 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 her conjunction, 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 northwardly, 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. The Moon's oblique motion with regard to the ecliptic, causes some difference in the times of her rising and setting from that which has been already mentioned. When she is northward of the ecliptic, she rises sooner, and sets later, than if she moved 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 and 225 days. 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 this 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 9 years and 112 days afterwards, 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 difference of times in Pisces and Aries, than if she moved in the ecliptic. When the ascending node is in Aries, the angle is only 9 degrees 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 difference of the Moon's rising in the same signs every 9 years, as there would be on two parallels 10 degrees from each other, if the Moon's course were in the ecliptic. The following table shows 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 equinoxes, and then either in the ascending node, or (highest part of her orbit,) and in the descending node, (or lowest part of her orbit.) M signifies morning; A afternoon, and the line at the foot of the table shows a week's difference in rising and setting. Moon's Full in her Full in her Full in the highest Full in the lowest part of her orbit. Rises at Sets at Rises at Sets at Rises at Sets at Rises at Sets at MH MH MH MH MH MH M 5 A 153 M 20/4 A 303 M 154 A 323 M 405 A 163 M01 age. H 12 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 black lead pencil. As there is a complete revolution of the nodes in 18 years, there must be a regular period of all the varieties which can happen in the rising and setting of the Moon during that time. At the polar circles, when the Sun touches the summer tropic, he continues twenty-four hours above the horizon; and the like number below it, when he touches the winter tropic. For the same reason, the full Moo1 being as high in the ecliptic as the summer's Sun, must therefore continue as long above the horizon; and the summer full Moon being as low in the ecliptic as the winter Sun, can no more rise than he does. But these are only the two full Moons which happen about the tropics, for all the others rise and set. In summer, the full Moons are low, and their stay is short above the horizon; then the nights are short, and we have the least occasion for moonlight. In winter, the full Moons run high, and they stay long above the horizon when the nights are long, and we need the greatest quantity of her reflected light. At the poles, one half of the ecliptic never sets, and the other half never rises; and therefore as the Sun is always half a year in describing one half of the ecliptic, and as long in going through the other half, it is natural to imagine that the Sun continues half a year together above the horizon of each pole in its turn, and as long below it; rising to one pole when he sets to the other. This would be exactly the case, if there were no refraction. But by the refraction of the Sun's rays, occasioned by the atmosphere, he becomes visible some days sooner, and continues some days longer in sight, than he would otherwise do: so, that he appears above the horizon of either pole, before he has got below the horizon of the other. And as he never goes more than 23 degrees and 28 minutes below the horizon of the poles, they have very little dark night; twilight being there, as well as at all other places, till the Sun be 18 degrees below the horizon. The full Moon being always opposite to the Sun, can never be seen while the Sun is above the horizon, except when the Moon falls in the northern half of her orbit; for when any point of the ecliptic rises, the opposite point sets. Therefore, as the Sun is above the horizon of the north pole from the 20th of March, till the 23d September; it is plain that the Moon when full, being opposite to the Sun, must be below the horizon during that half of the year. But when the Sun is in the southern half of the ecliptic, he never rises to the north pole; during this half of the year every full Moon happens in some part of the northern half of the ecliptic which never sets. Consequently, as the polar inhabitants never see the full Moon in summer, they have her always in the winter; before, at, and after the full, shining during 14 of our days and nights. And when the Sun is at his greatest distance below the horizon, being then in Capricorn, the Moon is at her first quarter in Aries, full in Cancer, and at her third quarter in Libra. And as the beginning of Aries is the rising point of the ecliptic, Cancer the highest, and Libra the setting point, the Moon rises at her first quarter in Aries, is most elevated above the horizon, and full in Cancer, and sets at the beginning of Libra in her third quarter, having continued visible for 14 diurnal rotations of the earth. Thus the poles are supplied one half of the winter time with |