FREE BOOKS

Author's List




PREV.   NEXT  
|<   119   120   121   122   123   124   125   126   127   128   129   130   131   132   133   134   135   136   137   138   139   140   141   142   143  
144   145   146   147   148   149   150   151   152   153   154   155   156   157   158   159   160   161   162   163   164   165   166   167   168   >>   >|  
times behind us, sometimes at a right angle in relation to the Sun and the Earth. Now, the eclipses of the Sun occur invariably at the time of New Moon, when our satellite passes between the Sun and ourselves, and the eclipses of the Moon, at the moment of Full Moon, when the latter is opposite to the Sun, and behind us. This fact soon enabled the astronomers of antiquity to discover the causes to which eclipses are due. The Moon, passing at the beginning of its revolution between the Sun and the Earth, may conceal a greater or lesser portion of the orb of day. In this case there is an eclipse of the Sun. On the other hand, when it is on the other side of the Earth in relation to the Sun, at the moment of Full Moon, our planet may intercept the solar rays, and prevent them from reaching our satellite. The Moon is plunged into _the shadow of the Earth_, and is then eclipsed. Such is the very simple explanation of the phenomenon. But why is there not an eclipse of the Sun at each New Moon, and an eclipse of the Moon at each Full Moon? If the Moon revolved round us in the same plane as the Earth round the Sun, it would eclipse the Sun at each New Moon, and would be itself eclipsed in our shadow at each Full Moon. But the plane of the lunar orbit dips a little upon the plane of the terrestrial orbit, and the eclipses can only be produced when the New Moon or the Full Moon occur at the line of intersection of these two planes, _i.e._, when the Sun, the Moon, and the Earth are upon the same straight line. In the majority of cases, instead of interposing itself directly in front of the sovereign of our system, our satellite passes a little above or a little below him, just as its passage behind us is nearly always effected a little above or below the cone of shadow that accompanies our planet, opposite the Sun. When the Moon intervenes directly in front of the Sun, she arrests the light of the radiant orb, and conceals a greater or less portion of the solar disk. The eclipse is partial if the Moon covers only a portion of the Sun; total if she covers it entirely; annular, if the solar disk is visible all round the lunar disk, as appears when the Moon, in her elliptical orbit, is beyond medium distance, toward the apogee. On the other hand, when the Moon arrives immediately within the cone of shadow that the Earth projects behind it, it is her turn to be eclipsed. She no longer receives the rays of the Sun, and this d
PREV.   NEXT  
|<   119   120   121   122   123   124   125   126   127   128   129   130   131   132   133   134   135   136   137   138   139   140   141   142   143  
144   145   146   147   148   149   150   151   152   153   154   155   156   157   158   159   160   161   162   163   164   165   166   167   168   >>   >|  



Top keywords:
eclipse
 

shadow

 

eclipses

 
eclipsed
 
portion
 
satellite
 

directly

 

planet

 

moment

 

passes


relation
 
opposite
 

covers

 

greater

 

apogee

 

immediately

 

arrives

 

projects

 

system

 

interposing


majority
 

receives

 

longer

 
sovereign
 

conceals

 
visible
 
radiant
 

annular

 

partial

 

straight


arrests

 

appears

 
effected
 
distance
 

passage

 
medium
 

intervenes

 

accompanies

 

elliptical

 

discover


antiquity

 

passing

 
beginning
 

lesser

 
conceal
 
revolution
 

astronomers

 

enabled

 
invariably
 

terrestrial