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Scene No. XIII.— The Moon at the Full.
We will now examine our moon, which may be justly designated the com-panion of the earth, in its annual course round the sun. Next to the sun itself,the moon is, to us, the most conspicuous of the heavenly bodies ; the changesshe undergoes in her appearance are more remarkable and more obvious thanthose of any other objects in the planetary system, and her apparent motions aremore rapid. Hence, the motions and changes of the moon engaged the attentionof astronomers before much was known to them of those of the sun ; and henceit was that the earlier inhabitants of the earth reckoned their time by theapparent motion of the moon, calculating by a lunar, not a solar year.
Astronomers concur in determining the distance of the moon from the earthto be 237,360 miles, about l-400th part of the distance of the earth from the sun.The moon’s diameter is computed to be 2,160 miles. That the moon is a bodyof a spherical figure we have very frequent opportunity of seeing; as well asthat she is subject to constant, regularly repeated variations of light andshadow. The most remarkable of the phenomena exhibited by the moon, arethese continual changes of figure ; sometimes she appears perfectly circular, atother times only half illuminated, or even resembling a thin thread of light,of a semicircular form, changing through all the gradations of figure betweenthose extremes : and as these changes of appearance are always found to bealike at the same elongation, or apparent distance from the sun, they provethat the moon receives her light from the sun; for as the moon is enlightenedon that side only which faces the sun, a greater or less quantity of thatenlightened part will be visible to us, according as it is turned towards us orfrom us, and her figure will, consequently, appear to vary through the wholeof her revolution.
It is a circumstance of familiar observation, that, during a few days of eachmonth, or lunation, we do not see the moon; even in the clearest weather, wehave, at those times, no moon-lighted nights : as it is said, there is no moon. Theexplanation of this case is, simply, that the moon is at that time in that part ofher orbit which lies between the earth and the sun, and is, therefore, invisibleto us, because her enlightened side is then turned wholly towards the sun, herunenlightened and invisible side towards the earth ; she is in the position termedher conjunction : a term already explained when speaking of the planet Venus .When this interval has passed, we first see the thin bright crescent which we termthe new moon, a little to the east of the sun, after he has set in the west, and alittle above the horizon, shewing the small visible portion of the illuminated partof her disc turned towards the sun. A few evenings after this, the moon appearsin the south, when the sun is in the west, and one-half the enlightened part ofher disc is then visible ; at the end of a few days more she appears in the east,when the sun is in the west, and with the round illuminated face which we callthe full moon. She is then in, what the astronomer terms, opposition; the
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