MON I'll, in chronology, the twelfth part of a year.
Time being duration, marked out for certain uses, and measured by the motion of the heavenly bodies, there thence re sults divers kinds of months as well as years, different from one another accord ing to the particular luminary by whose revolution they are determined, and the particular purposes they are destined for; hence months are of two kinds, astrono mical and civil. An astronomical month is that which is governed either by the motion of the sun or moon, and is con sequently of two kinds, solar and lunar : a solar month is that time in which the sun seems to run through a whole sign, or the twelfth part of the ecliptic. Hence, if regard be had to the sun's true ap parent motion, the solar month will be unequal, since the sun is longer in pass. ingthrough the winter-signs than through those of the summer ; but as he constant ly travels through all the twelve signs in 365 days, S hours, and 49 minutes, the quantity of a mean month will be had, by dividing that number by 12 ; on this prin ciple, the quantity of a solar month will be found to be SO days, 10 hours, 29 minutes, S seconds. A lunar month is that space of time which the moon takes up in performing its course through the zodiac, or that measured by the motion of the moon round the earth ; and is of three kinds, viz. periodical, synodical, and that of illumination. The lunar periodi cal month, is the space of time wherein the moon makes her round through the zodiac, or wherein she returns to the same point, being 27 days, 7 hours, 43 minutes, and S seconds.
The lunar synodical month, called also absolutely the lunar month and lunation, is the space of time between two conjunc tions of the moon with the sun ; or the time it takes from one conjunction with the sun to the next : of from one new moon to another : the quantity of a synodical month is 29 days, 12 hours, 44 minutes, 3 seconds, and 11 thirds. The quantity of a synodical month is not the same at all times, for in the summer sol stice,when the sun seems to move slowest, the synodical month appeareth less, be ing about 29 days, 6 hours, 42 minutes ; but in the winter, when the sun's motion seems faster, the moon does not fetch up the sun so soon, for which reason the synodical month then seems greater, vi:. 29 days, 19 hours, and 37 minutes, ac cording to the observation of the same astronomers : so that the first quantity given of the synodical month is to be understood as to the mean motion. From what has been said, it may easily appear that the difference between a periodical and synodical month is this ; the first is called periodical in respect of the moon's orbit ; but the synodical is so called in respect of its connection with the other luminary. Now, after the time of its con
junction, the sun does not continue in the same place of the zodiac, but moves for wards towards the east, upon which it falls out, that the moon, finishing its course, does not find the sun again in the same place where it left him, he being removed almost a whole sign from his former place, so that, to overtake the sun again, it plainly appears that a certain space of time is requisite besides the periodical, which makes up the synodical month.
A civil or political month, consists of a certain number of days, according to the laws and customs of the different coun tries wherein it is used, either having no regard to the solar or lunar months ; as those of the Egyptians in the equal year, of the Romans in the year of Romulus, &c. ; or coming pretty near to the solar astronomical month, as the Julian ; or else the lunar astronomical. as the Jewish, Turkish, and others. The British, and most European nations, make twelve months in the year, viz. January, Februa ary, &c. See .listesity, &c.
Civil solar months are such civil months as are accommodated to the astronomical months, or those which are to consist al ternately of thirty and thirty-one clays, excepting one month of the twelve, which, for every fourth year, consisted of thirty clays, and for the other years of twenty-nine. This form of civil months was introduced by Julius Cmsar; but un der Augustus, the sixth mouth, till then, front its place called Sextilis,.was denomi nated Augustus, in honour of that prince; and to make the compliment yet the greater, a day was added to it, so that it now consists of thirtpone days, though till then it had only thirty : to make up for which, a day was taken from Februa ry, so that from thenceforward it only consisted of twenty-eight days, and every fourth year of though be fore it had ordinarily consisted of twenty nine days, &c. and such are the civil or calendar months which now obtain throughout Europe.
Civil lunar months are to Consist al ternately of twenty-nine and thirty days : thus will two civil months be equal to two astronomical ones, abating for the odd minutes, and consequently the new moon will be hereby kept to the first day of each such civil month, for a long time to gether. However, to make them keep constant pace with the civil months, at the end of each nine hundred and forty eight months, a month of twenty-nine days must be added; or else every thirty third month must consist of thirty days. This was the month in civil or common use among the Jews, Greeks, and lto mans, till the time of Julius Cmsar.
MosTa, in law, is generally a lunar month of twenty-eight days, unless other expressed.