FREE BOOKS

Author's List




PREV.   NEXT  
|<   40   41   42   43   44   45   46   47   48   49   50   51   52   53   54   55   56   57   58   59   60   61   62   63   64  
65   66   67   68   69   70   71   72   73   74   75   76   77   78   79   80   81   82   83   84   85   86   87   88   89   >>   >|  
In this connection it must, however, be pointed out, in the first instance, that the eclipses which occur in any particular year are in no way associated with those which occurred in the previous year. In other words, the mere fact that an eclipse takes place upon a certain day this year will not bring about a repetition of it at the same time next year. However, the nicely balanced behaviour of the solar system, an equilibrium resulting from aeons of orbital ebb and flow, naturally tends to make the members which compose that family repeat their ancient combinations again and again; so that after definite lapses of time the same order of things will _almost exactly_ recur. Thus, as a consequence of their beautifully poised motions, the sun, the moon, and the earth tend, after a period of 18 years and 10-1/3 days,[5] to occupy very nearly the same positions with regard to each other. The result of this is that, during each recurring period, the eclipses comprised within it will be repeated in their order. To give examples:-- The total solar eclipse of August 30, 1905, was a repetition of that of August 19, 1887. The partial solar eclipse of February 23, 1906, corresponded to that which took place on February 11, 1888. The annular eclipse of July 10, 1907, was a recurrence of that of June 28, 1889. In this way we can go on until the eighteen year cycle has run out, and we come upon a total solar eclipse predicted for September 10, 1923, which will repeat the above-mentioned ones of 1905 and 1887; and so on too with the others. From mere observation alone, extending no doubt over many ages, those time-honoured watchers of the sky, the early Chaldeans, had arrived at this remarkable generalisation; and they used it for the rough prediction of eclipses. To the period of recurrence they give the name of "Saros." And here we find ourselves led into one of the most interesting and fascinating by-paths in astronomy, to which writers, as a rule, pay all too little heed. In order not to complicate matters unduly, the recurrence of solar eclipses alone will first be dealt with. This limitation will, however, not affect the arguments in the slightest, and it will be all the more easy in consequence to show their application to the case of eclipses of the moon. The reader will perhaps have noticed that, with regard to the repetition of an eclipse, it has been stated that the conditions which bring it on at e
PREV.   NEXT  
|<   40   41   42   43   44   45   46   47   48   49   50   51   52   53   54   55   56   57   58   59   60   61   62   63   64  
65   66   67   68   69   70   71   72   73   74   75   76   77   78   79   80   81   82   83   84   85   86   87   88   89   >>   >|  



Top keywords:

eclipse

 

eclipses

 
period
 

repetition

 

recurrence

 

regard

 

consequence

 
August
 

repeat

 

February


watchers

 

honoured

 

eighteen

 
Chaldeans
 
predicted
 

observation

 

arrived

 
extending
 

September

 

mentioned


affect
 

arguments

 
slightest
 

limitation

 

complicate

 

matters

 

unduly

 

stated

 

conditions

 
noticed

application

 

reader

 

generalisation

 
prediction
 

astronomy

 
writers
 
interesting
 

fascinating

 

remarkable

 
orbital

resulting

 
behaviour
 
system
 

equilibrium

 

naturally

 

combinations

 

definite

 
lapses
 
ancient
 

family