Tin-; STAR VAITLT. 3 



round when the sun in hin course passes those accurateh' 

 determined points in the heavens called also equinoxes. It 

 will dwell in your recollection, moreover, no doubt, that one 

 eciuinox, the vernal, is called the fii-st point of the sign Aries ; 

 the other, the autumnal, the first point of the sign Libra. 



It follows from all this that the belt of the zodiac, about i8 

 degrees in width, or nine degrees on each side of the ecliptic, 

 is always half above and half below the equator. Let me say 

 that the visible portion, regarded as a whole, is a semicircle seen 

 in perspective — that is to say, a semiellipse, standing on the 

 platform of the horizon like an arch whose crown is 23° 30' 

 above the same, and- seeming to slide in that position so as 

 constantly to make the circuit of the heavens. 



When the sun is coming towards, and reaches, the 

 equator, he will be seen by the observer at the pole in the 

 horizon ; and will, to all appearances, make one daily circuit 

 in that position. But he is constantly changing declination 

 on the ecliptic, and will, next day, be clear of the equator; 

 and next day still farther away from it. The result is that he 

 rises in a slow spiral until at the solstice, or sun-halt, he is- 

 23° 30' above the horizon. He then turns and goes down 

 again, by the same steps but in a reversed spiral, to the 

 equator, where, at the other equinox, he disappears for six 

 months from the view. He then offers, in turn, the same 

 phases to the eye of one at the opposite pole. 



And, generally, it will be sufficient to discuss what is to 

 take place at points of the northern hemisphere ; the same 

 being true of the southern, with the proper change of data. 



The plane of the moon's orbit is inclined to the plane of 

 the ecliptic 5° 9'. This means that the moon moves on the 

 starry vault within a belt or zone 10° 18' wide, half on one 

 side of the ecliptic, half on the other. The moon covers, at 

 one time or another, every point of this zone. It follows from 

 what has been said that, as the ecliptic is always half above 

 and half below the horizon, its highest point being at an 

 altitude of 2-^° ^o', the moon will almost imitate the motions 



