Astronomy. [Lecture 20. 



year, she is quite invisible. In summer they 

 rise about midnight, and the sun being then 

 three signs, or a quarter of a circle before, them, 

 the moon is in them about her third quarter; 

 when rising so late, and giving but very little 

 light, that rising passes unobserved. In autumn 

 these signs, being opposite to the sun, rise when 

 he sets, with the moon in opposition, or at the 

 full, which renders her rising very conspicuous. 



Hitherto, for the sake of being perfectly in- 

 telligible, I have supposed the moon to move in 

 the ecliptic, from which the sun never deviates. 

 But the orbit in which the moon really moves is 

 different from the ecliptic; one half being ele- 

 vated 5 l-8d degrees above it, and the other half 

 as much depressed below it. The moon's orbit 

 therefore intersects the ecliptic in two points 

 diametrically opposite to each other ; and these 

 intersections are called the moon's nodes. So 

 the moon can never be in the ecliptic but when 

 she is in either of her nodes, which is at least 

 twice between every two successive changes, and 

 sometimes thrice. For, as the moon goes almost 

 a whole sign more than round her orbit from 

 change to .change; if she passes by either node 

 about the time of change, she will pass by the 

 other in about fourteen days after, and come 

 round to the former node two days again before 

 the next change. That node from which the 

 moon begins to ascend northward or above the 

 ecliptic, in northern latitudes, is called the 



