Except at the exact time of full moon, we do not see the entire face of our satellite; one edge or 'limb' is in darkness. As the moon therefore passes over the star, either the limb at which the star disappears, or that at which it reappears, is invisible to us. To watch an occultation at the bright limb is pretty; the moon, with its shining craters and black hollows, its mountain ranges in bright relief, like a model in frosted silver, slowly, surely, inevitably comes nearer and nearer to the little brilliant which it is going to eclipse. The movement is most regular, most smooth, yet not rapid. The observer glances at his clock, and marks the minute as the two heavenly bodies come closer and closer to each other. Then he counts the clock beats: 'five, six, seven,' it may be, as the star has been all but reached by the advancing moon. 'Eight,' it is still clear; ere the beat of the clock rings to the 'nine,' perhaps the little diamond point has been touched by the wide arch of the moon's limb, and has gone! Less easy to exactly time is a reappearance at the bright limb. In this case the observer must ascertain from the _Nautical Almanac_ precisely where the star will reappear; then a little before the predicted time he takes his place at the telescope, watches intently the moon's circumference at the point indicated, and, listening for the clock-beats, counts the seconds as they fly. Suddenly, without warning, a pin-point of light flashes out at the edge of the moon, and at once draws away from it. The star has 'reappeared.' Far more striking is a disappearance or reappearance at the 'dark limb.' In this case the limb of the moon is absolutely invisible, and it may be that no part of the moon is visible in the field of the telescope. In this case the observer sees a star shining brightly and alone in the middle of the field of his telescope. He takes the time from his faithful clock, counting beat after beat, when suddenly the star is gone! So sudden is the disappearance that the novice feels almost as astonished as if he had received a slap in the face, and not unfrequently he loses all count or recollection of the clock beats. The reappearance at the dark limb is quite as startling; with a bright star it is almost as if a shell had burst in his very face, and it would require no very great imagination to make him think that he had heard the explosion. One moment nothing was visible; now a great star is shining down serenely on the watcher. A little practice soon enables the observer to accustom himself to these effects, and an old hand finds no more difficulty in observing an occultation of any kind than in taking a transit.