314 Astronomy. [[Lecture 20. 



then said to be at the t /w//. In proportion as she 

 approaches the sun, only a part of her surface 

 will be enlightened, as at P, when not more than 

 half will be in that state. She is then said to be 

 in her last quarter. In fine, the enlightened parts 

 become less and less* to a spectator on the earth 

 as she advances towards the sun, till at last she 

 comes between the sun and the earth at N, when 

 she is altogether invisible, and this last phasis 

 is called the new moon. She has not long passed 

 this point before she begins to present a small 

 portion of her surface enlightened. When she 

 is at Q, she is said to be in her first quarter, 

 and the enlightened part continues augmenting 

 till she is again at the full. 



When the moon is placed between the four 

 parts A, B, C, D, and at an equal distance from 

 each point, she is said to be in her octants. In 

 the first A, and in the fourth, D, she presents 

 only one-eighth of her surface enlightened, and 

 in the second, B, and the third, C, three-eighths 

 of her surface are enlightened. 



In the phases A, Q, B, which are between the 

 new and full moon, the convexity of the en- 

 lightened part is turned towards the west, and 

 in those of C, P, D, which are between the full 

 and the new moon, this convexity is directed 

 towards the east. All these changes, or phases, 

 will be rendered more evident to the student, 

 if he will in every position of the moon, imagine 

 tangents to the moon's orbit, drawn through her 



