THE HARVEST MOON. VERY one is familiar with the general facts relating to the harvest moon. In some parts of the country it is said in popular rhyme that "The Michaelmas moon, Nine nights rises soon." Long before astronomers wrote on the subject, farmers and labourers used to observe the early rising of the full moon in the beginning of Autumn, and they called it "The Harvest Moon," from its usefulness in assisting them to gather in the fruits of the earth. The peculiarity at this season is, that the moon rises before or very soon after sunset for several evenings together, and that the interval between the time of rising on successive nights is less than at other times of the year. These results are produced by astronomical arrangements, the principles of which will be readily understood. The plane of the equinoctial is at right angles to the earth's axis, and as the earth turns round its axis, all parts of the equinoctial make equal angles with the horizon, both at rising and setting, so that equal portions of it always rise or set in equal times. The moon in her orbit seems to move at the rate of 12 degrees 11 minutes of space from the sun every day; and 12 degrees 11 minutes of the equinoctial rise or set in fifty minutes of time in all latitudes. If the moon's motion were equable, and in the equinoctial, she would regularly rise and set fifty minutes later every day than on the day preceding. This is the case at places on the Equator. But the moon's motion is not on the equinoctial plane, but more near that of the ecliptic, which has a certain obliquity to the earth's axis. Owing to this obliquity, or slanting of the plane of the ecliptic, its different parts make very different angles with the horizon as they rise or set; that is, when they appear to view or disappear at any given place on either side of the equinoctial line. Those parts of the ecliptic, or signs of the Zodiac with the smallest angle, set with the greatest, and vice versa. In equal times, whenever this angle is least, a greater portion of the ecliptic rises than when the angle is THE HARVEST MOON. larger, as may be seen by elevating the pole of a globe to any considerable latitude, and then turning its axis. Consequently, when the moon is in those signs which rise or set with the smallest angles, she rises or sets with the least difference of time; and with the greatest difference in those signs which rise or set with the greatest angles. In northern latitudes the smallest angle made by the ecliptic and horizon is when Aries rises, at which time Libra sets; the greatest when Libra rises, at which time Aries sets. The ecliptic rises fastest about Aries and slowest about Libra. On the parallel of London, as much of the ecliptic rises about the adjoining signs, Pisces and Aries, in two hours, as the moon goes through in six days; and therefore, while the moon is in these signs, she differs but two hours in rising for six days together; that is, about twenty minutes only, on the average, later every day or night, than on the preceding. In fourteen days after, when the moon comes to the parts of the ecliptic known as Virgo and Libra, the opposite signs to Pisces and Aries, she differs almost four times as much in rising; namely, about one hour and a quarter later every day or night than on the preceding, while she is in these signs. In October, it will be observed that the moon also rises early, and with short intervals of difference, on successive nights. The October moon is often called "The Hunter's Moon." These are the only two full moons in the year which can rise so near the time of sunset for a week together. The reason is, that the sun is in the signs Virgo and Libra in our autumnal months, and as the moon can never be full except when she is opposite the sun, she can only be full in the opposite signs Pisces and Aries, in these two months. As the moon is in Pisces and Aries during every one of her monthly revolutions, the question may occur, how is the remarkable rising at short intervals for successive nights only perceived at harvest? The reason is, that in Winter these signs rise at noon, when the rising of the moon 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 season of the year, she is quite invisible. In Summer the signs of Pisces and Aries rise about midnight, and the sun being then three signs or a quarter of a circle before them, the moon is then in her third quarter; when, rising so late, and giving but very little light, her rising passes unobserved. But 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 conspicuous. With active vigour crushes down the tree; Hence from the busy, joy-resounding fields, |