on the parallel of London, for 28 days, in which time the Moon finishes her period round the ecliptic, & gets 9 degrees into the same sign from the beginning of which she set out. It appears by the table, that when the Moon is in Virgo and Libra, she rises one hour and a quarter later 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. 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 and degrees,) so that the Moon must go 27 and degrees more than round, and as much farther as the Sun advances in that interval; which is 2 degrees and is 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. 1 15 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 risc, 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; 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 and 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 ecliptic 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 came round to the former node two days again be fore 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 and 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 orbt, makes an angle of 5 and de grees 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 & Aries, than she would do if she kept in the ecliptic. But in 9 years and 112 days afterward, the descending node comes to Aries, and then the Moon's orbit makes an angle of 5 and 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 and degrees on the parallel of London when Aries rises. But when the descending node comes to Aries, the angle is 20 and degrees; this occasions as great difference of the Moon's rising in the same signs every 9 years, as these would be on two parallels 10 and 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 least 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. moons Full in her ascending node. Full in the highest Full in her descending node Full in the lowest part of her orbit age Rises at Sets at Rises at Sets at Rises at Sets at Rises al Sets at 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 Moon 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 Moon-light. 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 N |