CHAPTER IX. 



AN EVENING AVITH THE TELESCOPE. 



THE opportunities for observing the planet Saturn are not 

 nearly so frequent as those in which the moon may be 

 advantageously observed. We must choose the time when 

 Saturn comes nearest to the earth. This will take place 

 when the earth lies nearly between Saturn and the sun. 

 Supposing that such an occurrence is now taking place, 

 the earth will in a short time have moved away from the 

 best position, and the distance from the earth to the 

 planet will be on the increase. When a year has elapsed 

 the earth will have returned to its original position, but 

 it will not then be exactly between Saturn and the sun, 

 for the great planet has moved. Like the earth, Saturn 

 also revolves round the sun, but the magnitude of his orbit 

 is much greater than that of the earth, and consequently 

 the time that Saturn requires to complete a single revo- 

 lution is about twenty-nine and a half of our years. 

 Hence it follows that Saturn will have moved in the 

 course of the year, so that the earth must pursue its 

 journey for another twelve or thirteen days before it will 

 again have resumed its position between the planet and 

 the sun. 



