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penumbramore about penumbra

penumbra


  2  definitions  found 
 
  From  Webster's  Revised  Unabridged  Dictionary  (1913)  [web1913]: 
 
  Penumbra  \Pe*num"bra\,  n.  [NL.,  fr  L.  paene  almost  +  umbra 
  shade.] 
  1.  An  incomplete  or  partial  shadow. 
 
  2.  (Astron.)  The  shadow  cast,  in  an  eclipse,  where  the  light 
  is  partly,  but  not  wholly,  cut  off  by  the  intervening 
  body;  the  space  of  partial  illumination  between  the  umbra, 
  or  perfect  shadow,  on  all  sides,  and  the  full  light.  --Sir 
  I.  Newton. 
 
  Note:  The  faint  shade  surrounding  the  dark  central  portion  of 
  a  solar  spot  is  also  called  the  {penumbra},  and 
  sometimes  {umbra}. 
 
  3.  (Paint.)  The  part  of  a  picture  where  the  shade 
  imperceptibly  blends  with  the  light. 
 
  From  WordNet  r  1.6  [wn]: 
 
  penumbra 
  n  :  a  fringe  region  of  partial  shadow  around  an  umbra 




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