A compendium of astronomy; containing the elements of the science, familiarly explained and illustrated, with the latest discoveriesAdapted to the use of schools and academies, and of the general reader . aid to be in conjunction, and when inopposition ? What are the syzigies, quadratures, and octants ?Define the circle of illumination, and the ciicle of the disk. PHASES. 121 sun, her narrow thread of light is lost in the solar blaze ;and finally, at the moment of passing the sun, the darkside is wholly turned towards us, and for some time welose sight of the moon. The two points in the orbit
A compendium of astronomy; containing the elements of the science, familiarly explained and illustrated, with the latest discoveriesAdapted to the use of schools and academies, and of the general reader . aid to be in conjunction, and when inopposition ? What are the syzigies, quadratures, and octants ?Define the circle of illumination, and the ciicle of the disk. PHASES. 121 sun, her narrow thread of light is lost in the solar blaze ;and finally, at the moment of passing the sun, the darkside is wholly turned towards us, and for some time welose sight of the moon. The two points in the orbit corresponding to new andfull moon respectively, are called by the common nameof syzigies; those which are 90° from the sun arecalled quadratures ; and the points half way betweenthe syzigies and quadratures are called octants. Thecircle which divides the enlightened from the unen-lightened hemisphere of the moon, is called the circle ofillumination: that which divides the hemisphere thatis turned towards us from the hemisphere that is turn-ed from us, is called the circle of the disk. 153. As the moon is an opake body of a sphericalfigure, and borrows her light from the sun, it is obvious Fig. 31. that that half only which is towards the sun can be il-luminated. More or less of this side is turned towardsthe earth, according as the moon is at a greater or lesselongation from the sun. The reason of the differentphases will be best understood from a diagram. There-fore let T (Fig. 31,) represent the earth, and S the sun, 11 122 THE MOON. Let A, B, C, &c. be successive positions of the A the entire dark side of the moon being turned to-wards the earth, the disk would be wholly invisible. AtB, the circle of the disk cuts of a small part of the en-lightened hemisphere, which appears in the heavens atb, under the form of a crescent. At C, the first quarterthe circle of the disk cuts off half the enlightened hem-isphere, and a half moon is seen at c. In like manner itwill be
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectastronomy, bookyear18
