Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/565

 471 ASTRO N O M Y. catifes .fome difference in the times of her rifing and places between tbs polar circles. But, during the above tic, from what is already mentioned. For whilft lire fourteen days, the moon is 24 fydereal hours later in isfetting northward of the ecliptic, fire rifes fooner and fets fetting ; for the fix figns, which rife all at once on the later than if fire moved in the ecliptic; and when file is eaftern fide of the horizon, ve 24 hours in fetpng fouthward,of fite rifes later, and fets fooner. on the weftern fide of it; as any one may fee by ma- This differencetheisecliptic, even in the fame figns, beking chalk-marks at the beginning of Capricorn and of caufe the nodes fiiiftvariable, backward about 194 degrees in th<r Cancer, and then, having elevated the pole 66i degrees, ecliptic every year; and round it contrary to the turn the globe flowly round its axis, and obferve the fi- order of figns in 18 yearsfo225go days. fing and fetting of the ecliptic. As the beginning of When the afcending node is in Aries, the fouthern Aries is equally diftant from the beginning of Cancer of the moon’s orbit makes an angle of y-j- degrees and of Capricorn, it is in the middle of that half of the half with the horizon than the ecliptic does, when Athe ecliptic which rifes all at once. And when the fun is • lefs at the beginning of Libra, he is in the middle of the o- ries rifes in northern latitudes: For which reafon the ther half. Therefore, when the fun is in Libra, and moon rifes with lefs difference of time whilft file is in the moon in Capricorn, the moon is a quarter of a cir- Pifces and Aries, than there would be if fiie kept in the 9 years and x 12 days afterward, the cle before the fun; oppofite to him, and confequently ecliptic. Butin node comes to Aries; and then the moon’s full in Aries, arid a quarter of a circle behind him, when defcending makes an angle degrees greater with the horiin Cancer. But when Libra rifes, Aries fets, and all orbit that half of the ecliptic of which Aries is the middle ; zon when Aries riles, that the ecliptic does at that time;;, and therefore, at that time of -the year, the moon rifes which caufes the moon to rife with- greater difference of time in Pifces and Aries than if (he moved in the eat fun-fet from her firft to her third quarter. In northern latitudes, the autumnal full moons are in cliptic. Pifces and Aries, and the vernal full moons in Virgo and To be a little more particular ; when the afcending node; Libra: In fouthern latitudes juft the reverfe, becaufe is in Aries, the angle is only 94 degrees on the parallel the feafons are contrary. But Virgo and Libra rife at of London when Aries rifes. But when the defcending; as fmall angles with the horizon in fouthern latitudes, as node comes to Aries, the angle is 204 degrees ; this ocPifces and Aries do in the northern; and therefore the cafibns as great' a difference of the moon’s rifing in the harvelt-moons are juft as regular cm one fide of the eqiiar fame figns every 9 years, as there would be on two parallels to iOj degrees from one another, if the moon’s tor as on the other. As thefe figns, which rife with the leaf! angles, fe't Courfe were in the ecliptic. with the greateft, the vernal full moons differ as much As there is a complete revolution of the nodes in 184 in their times of rifing every night,, as the autumnal full years, there mu ft, he a regular period of all the varieties moons differ in their times of fetting; and fet withas which can happen in the rifing and fetting of the moon little difference as the autumnal full moons- rife; the one during that time. But this lifting of the nodes never affeds the moon’s rifing fo much, even in her quickeft being in all cafes the reverfe of the other. Hitherto, for the fake of plainnefs, we have, fuppofed defcending latitude, as not to allow us ftill the benefit ofr the moon to move in the ecliptic, from which the fun her rifing nearer the time of fun-fet for a few days togenever deviates. But the orbit in which the moon really ther about the full in harveft, than when Ihe is full at amoves is different from the ecliptic; one half being ele- ny other time of the year. The following table fiiews vated degrees above it, and the other half, as much in what years the harveft-moons are leaft beneficial as to depreffed below it. The moon’s orbit therefore inter- the times of their riling, and in what years moft, from feffs the ecliptic in two points diametrically oppofite to 1751.101861. The column-of years under the letter each other ; and thefe interfections are called the moon's L are thofe in which the harveft-rrroons are leaft of all nodes.1 So the moon can never be in the ecliptic but beneficial, becaufe they fall about the defcending node; when fhe is in either of her nodes, which is at leaft and thofe under M are the moft of all beneficial, becaufe ; twice in every courfe from- change to change, ,and fome- they fall about the afcending node. In all the columns, times thrice. For, as the moon goes almoft a whole from N to S, the harveft-moons defeend gradually in fign more than round her orbit from change to change, if the lunar orbit,, and rife to lefs heights above the horiflie paffes by either node about the time of change, fire zon. From S tfl N they afcend in the fame proportion,, will pafs by the other in about' fourteen days after, and and rife to greater heights above the horizon. In both come round to the former node two days again before the columns under S, the harveft-moons are in the loweft. the next change. That node, from which the moon be- part of the moon’s orbit, that is, fartheft fouth of the. gins to afcend northward, or above the ecliptic, in nor- ecliptic; and therefore ftay ihorteft of all above the hothern latitudes, is called the afcending-node ; and the o- rizon ; in the columns under N, juft the reverfe. And, ther, the defending node ; becanfe the moon, when fire in both cafes, their rifing, though not at the fame times, pafies by it, defcends below the ecliptic fouthward. are nearly the fame whh regard to difference of time,' as The moon’s oblique motion, with regard to the eclip- if the moon’s .orbit were coincident with the eclipti c. Tears