20 Astronomy. [Lecture 24-. 



fact, the sun and moon are more than seventeen 

 degrees from either of the nodes at the time of 

 conjunction, the moon is then too high or too 

 low in her orbit for any part of her shadow to 

 fall on the earth ; and when the sun is more 

 than twelve degrees from either of the nodes at 

 the time of opposition, the moon is too high, or 

 too low, to pass through any part of the earth's 

 shadow. Her orbit contains 360 degrees; of 

 which seventeen, the limit of the solar eclipses 

 on either side of the nodes, and twelve, the liny t 

 of lunar eclipses, are but small portions ; and as 

 the sun passes by the nodes but twice in a year, 

 it is no wonder that we have several new and 

 full moons without eclipses. 



An eclipse of the moon then can only take 

 place at its full, and when the moon is in oppo- 

 sition to the sun, and the moon is found either in 

 one of his nodes, or near it. Suppose EE (PL III. 

 fig. 6) to be a portion of the ecliptic at the di- 

 Btance of the moon, along which the shadow of 

 the earth is moving. This shadow is repre- 

 sented by the black circular spots ABCD, which 

 may be conceived to be sections of the cone 

 DCE in fig. 7, where S is the sun, and T the 

 earth. Suppose again the line LL (fig. 6) to be 

 a portion of the orbit of the moon, which cuts 

 the ecliptic EE in the point N, called the node, 

 making with it an angle of a little more than 

 five degrees. If, in the moment of her oppo- 

 sition, the moon be found in the point F in her 



