YET A YEAR LATER. 79 



twenty-nine and a half days. Speaking roughly, we 

 may say that once a fortnight the imagined observer 

 in the sun would see the moon crossing the earth's 

 place. He would always see the moon close to the 

 earth, since we have seen that the whole length of the 

 moon's path, as seen from the sun, is much less than 

 the breadth of the sun's globe as we see it ; but twice 

 in a month the moon would be very close by the earth. 

 Now our observer in the sun would see that the 

 mooji's path passed from its greatest opening to a 

 seeming line, and thence to its greatest opening again 

 (but with opposite tilt) in five months and about three 

 weeks; passing back to a seeming line and to its 

 original opening again, in all respects as at first, in 

 the same time. Eleven months and eleven days com- 

 plete the whole set of changes. When the path seemed 

 most open the moon would not at any time actually 

 cross the earth's face, or pass actually behind it. In 

 other words, the moon would neither hide any part of 

 the earth from the sun nor be hidden by the earth. 

 Hiding any parts of the earth from the sun means 

 obviously eclipsing the sun as viewed from those parts 

 of the earth ; while to say the moon is hidden from 

 the sun by the earth means (no less obviously) that 



We may thus compare it to the outer rim of Saturn's ring-system ; and 

 precisely as we see that ring-system closing up and opening out sys- 

 tematically in the course of about twenty-nine years, so certainly an 

 observer on the sun, watching our moon's course, would find her path 

 opening out and closing up systematically in the course of eleven 

 months eleven days, the seeming length of the path remaining appre- 

 ciably unchanged, and about equal to three-fifths of the seeming 

 diameter of the sun as seen from the earth. 



