630 THE AGE OF THE SUN. 



here, the brilliant planet will present the strange appearance of being ut- 

 tei-ly extinguished, in the short space of half a minute, without obvious 

 cause, Venus being 0.4 degrees distant from the nearest point of the lunar 

 cresent. If the dark part of the moon should be faintij' perceptible we 

 shall then have a chance to see the old "Dragon" of ancient stellar lore 

 literally eating its way into the Hesperian star, and swallowing her up into 

 utter darkness. 



The planet will remain behind the moon for one hour and two minutes. 

 as seen from Kansas City. At about fitteen minutes past seven o'clock the 

 planet will peep out from behind the southern horn of the moon, near the 

 position shown in our second diagram, and occupy 1.3 minutes in emerging, 

 the motion outward being very oblique. Her position at emersion will be 

 156 degrees from the astronomically north point of the moon's limb ; and 

 15|- degrees east from the point of the limb which is nearest to the horizon. 

 At this time the naoon's altitude will be only 8.7 degrees from the horizon. 



The time and phase of the event vary materially with the point on the 

 earth's surface on which the observer is situated. The reason for this is 

 found in her relatively small distance from the earth, which causes an angu- 

 lar change in her jsosition equal to her whole diameter, corresj^onding to a 

 difference of about thirty-three degrees in latitude on the earth's surface. 

 Two observers may be separated by thirty-three degrees of latitude, and 

 one of them see a star apparently on the southern limb of the moon, at the 

 same instant that the other observer sees the same star on her northern 

 limb. It is this fact that makes the calculation of an occultation, or solar 

 eclipse, a lengthy one, involving the solution of several spherical triangles, 

 and making a knowledge of the calculus highly desirable, though not an 

 absolute necessity. The apparent position of the moon, with reference to 

 the star or planet, at any instant varies with the position of ihe observei' 

 on the earth's surface. 



The occultation of Yenus by the moon, when both are favorably situated 

 for observation, is a very rare phenomenon. The last ex-hibition of the 

 kind witnessed here occurred seventeen years ago, in April, 1860. The 

 planet was then, as now, near her greatest eastern elongation from the sun, 

 and the moon four days old; but both were much' higher than they will be 

 to-night, as they were near the northern solstice. 



The distance of Yenus from the earth at the time will be about 257 times 

 that of the moon, the respective distances being 63,000,000 and 240,000. 

 This fact enables us to account for the apparently small size of Yenus, 

 though her lineal diameter is to that of the moon as 362 to 100. 



THE AGE OF THE SUN. 



There has been a long disj)ute between the phj'sicists and inathematicians 

 on the one hand and the geologists and biologists on the other, as to the age 

 of the eai'th, or rather, since that is equally involved, the age of the sun. 



