the Corona is a Solar or Terrestrial Phenomenon, 119 



Let A be a point on the earth where the sun is eclipsed ; 

 B C, limit of earth's atmosphere ; 

 D, the moon ; 

 H E, photosphere of sun ; 

 E F, the apparent corona. 



Now, if the corona be terrestrial, the light producing it must 

 be reflected or separated from the atmosphere within the triangle 

 ABC. 



Join B D and produce to G. 



Then G is the most distant point from the limb on the sun's 

 disk from which light is reflected to A by the atmosphere ; and 

 if the triangle E A F or angular extent of the corona from the 

 sun is given, we can find Z. E A G. 



The angles being small, ^ EA]F = |rjr approximately. 



■ 



GE:CB::ED:DC, therefore G E = C B ^~, . (1) 

 and 



EF:CB::EA:CA, therefore EF = CB^; . (2) 



and ED = E A—AD; and AD being small in proportion to 

 E A, E D may without great error be taken as equal to E A. 

 Dividing (1) by (2), 



height of atmosphere 

 dist. of moon — height of atm. 

 CA 



ZEAG_ height of atmosphere 



Z.E A F dist. of moon— height of atmosphere 



EAG^EAF-, height of atmosphere 



dist. or moon — height of atmosphere 



If, for example, we now take 



EAF =30', 



and 



Height of atmosphere .... =100 miles, 

 and 



Dist. of moon — height of atmosphere =240,000 miles, 

 then 



ZEAG = 30 '2W = (y '- 75 - 



GE 



E D or E A 

 DE 



CA 



EF~ 



EA 



"DC 



