Diagram Illustrating the Harvest Moon.
“The little circles M show the moon at several successive positions in her orbit, just twenty-four hours apart. You perceive that in consequence of the slight inclination to the eastern horizon the sinking of the latter caused by the earth’s rotation will bring the moon into view night after night at almost the same hour. In fact, in high northern latitudes like those of Norway and Sweden the moon’s path at this time of the year may actually coincide with the horizon, so that for several evenings she will rise at exactly the same hour. The name ‘Harvest Moon’ explains itself, since it always occurs at the time of the autumn harvests and the vintage, and seems to supplement the fading daylight for the benefit of late laborers in the fields. The ‘Harvest Moon’ does not occur every year at precisely the same date. It is very rare that Full Moon happens to fall just on September 22d. It usually either precedes or follows that date. The ‘Harvest Moon’ is the Full Moon which occurs nearest to the Autumn Equinox, either before or after. The ‘Hunter’s Moon’ is the first Full Moon which follows the ‘Harvest Moon.’ Like the former it rises for several successive evenings near the same hour, but this phenomenon is less marked in the case of the ‘Hunter’s Moon,’ because it is farther from the Equinox.”
“Thank you, again,” said my friend. “I shall never henceforth look at the moon without thinking of circles, straight lines, and arrows as well as of ‘ring mountains’ and ‘seas.’”
“Then you are making good progress toward science,” I replied. “One last look, now, at the photograph of the Old Moon’s sickle, and then we had better postpone our examination of the large photographs, showing certain particularly interesting districts on the moon, until to-morrow morning. There is here another interesting point for artists to note. The convex side of the sickle of the Old Moon, or the New Moon, is always an arc of a circle, but the concave side is never circular although it is often thus represented. The concave side, neglecting its irregularities arising from the differences of level and of brilliancy of the lunar surface, is elliptical in outline, that is to say, it is a semicircle viewed obliquely.”
“Whatever its geometry may be,” replied my friend, “it is certainly very beautiful. Good night, and I shall demand to see those large photographs before the sun is very high to-morrow.”
IV
GREAT SCENES ON THE MOON