14 THE SKY. 



us on the earth, according to the position in which we 

 view it ; thus, in fig. 12, E represents the central position 

 of the earth, and s the direction from which the light of the 

 sun comes, the outer circle of moons represents the various 

 real positions of that luminary with respect to the earth 

 and sun, and the inner circle shows its appearance when in 



FIG. 12. 



these various positions. When the moon is between the 

 earth and sun, as at , it is said to be in " conjunction," and 

 as the darkened side is towards the earth, of course it is not 

 visible, this is "new moon" (a corruption of "no moon") ; 

 when at I b, but a small part of the illuminated half is seen, 

 and it is then said to be " crescentic " (first and last quarter) ; 

 at c c, half of the bright side is seen, the moon is said to be 

 at " quadrature," and the appearance is that of a "half-moon ; " 

 at d d, the greater part of the bright side is seen, and it is 

 called " gibbous " and appears as a " three-quarter-moon," 

 and at e the whole of the illuminated side is seen ; it is then 

 " full-moon," and is said to be in " opposition." 



Beyond the earth the planet Mars (fig. 13) moves in its 

 orbit round the sun ; it is the smallest, but one, of the larger 



