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CHAPTER VI.

The Harvest Moon.

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THE Moon moves in her orbit (13° 10′ 35′′ in each solar day of 24 hours. But as the motion of the Earth in the ecliptic, at the same time, is 59′ 8′′, the apparent motion of the Sun, the excess of her motion over that of the Earth, or the Sun's apparent motion, is 12° 11′ 27". A meridian of the Earth, in its diurnal rotation, moves this in 48′ 38′′ of time. But, the Moon at the same time moving forward, the meridian will not overtake her till 50′ 28′′. The Moon rises at the equator, therefore, about 50′ 28′′later on each succeeding day, than it did on the preceding, at all seasons of the year. But the case is very different in high latitudes. Farmers in those latitudes have long observed (the early rising of the autumnal full moon.) "In this instance, says Mr. Ferguson, "as in many others, discoverable by astronomy, the wisdom and beneficence of the Deity are conspicuous, who ordered the Moon so as to bestow more or less light on all parts of the Earth, as their several circumstances and seasons render it more or less serviceable. About the equator, where there is no variety of seasons, and the weather changes seldom, and at stated times, moonlight is not necessary for gathering in the produce of the ground; and there the Moon rises about 50 minutes later every day or night than on the former. In considerable distances from the equator, where the weather and seasons are more uncertain, the autumnal full Moons rise very soon after sunset for several evenings together. At the polar circles, where the mild season is of short duration, the autumnal full Moon rises at sunset from the first to the third quarter."

The horizon of any place forms angles with the plane

of the Moon's orbit, differing from each other at different parts of the day, and at different seasons of the year. From the varied position of these circles) arise the phenomena of the harvest Moon. About the 23d of September, when the Sun enters Libra, the Earth enters Aries. At any place in north latitude, the angle between the horizon and the Moon's orbit is less, at that season of the year, about the time of sunset, than at any other time of the day. The full Moon, about the autumnal equinox, being in that part of her orbit opposite the Sun, must rise at this angle in latitudes below the Arctic circle. The angle decreases from the equator to this circle, where it vanishes. While the Moon remains in this part of her orbit, in all places where the angle is small, her diurnal motion will make but little variation in the time of day when she rises, on each succeeding evening.

To illustrate the phenomena of the harvest Moon, put small pieces of paper on the ecliptic of a terrestrial) globe, on each side of the first degree of Aries, at 120 11' 27" from each other, representing the Moon's diurnal motion from the Sun; rectify the globe for the latitude of the place, suppose 45°. With the number of papers or pieces of paper corresponding to the days of a week, bring the westernmost to the eastern horizon; set the index of the hour circle at the time of the Moon's rising, on the evening nearest to three and a half days before her arrival at the first degree of Aries. Turn the globe westward, which will be the same in effect as the rotation of the horizon eastward in respect to the Moon, till the second paper is brought to the horizon; the index will point to the time of the Moon's rising on the succeeding evening. Bring in succession the papers to the horizon; the index will show the time of the Moon's rising on the succeeding days of the week. The inclination of the Moon's orbit to the plane of the ecliptic will not materially affect this rep

resentation.

When the full happens at the equinox, the Moon ar

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