//POV-Ray 3.1
//northern lights media
//Kurt Bangert 
//http://www.travelnotes.de/

#include "colors.inc"
#include "textures.inc"

camera {location <0,2.5,-30>
look_at <0,2.5,0>}  
//a light source only when other objects are present
//light_source { <0,10,-50> color rgb <.2,.2,.2> }
 
//aurora medium
#declare blue_light= media {
      emission .4
      density {
      gradient y 
      turbulence <.3,.06,.3> 
        color_map {                   
         [0.0  color rgb <0, 0, 0>]
         [0.2 color rgb <0, 0, 0>]  
         [0.3  color rgb <.15,.4,.8>]  
         [0.6  color rgb <.05,.12,.2>]
         [1.0  color rgb <.04,.08,.16>]
        }}}  
 
//csg half-moon-like element
#declare element1=
 difference { 
 cylinder {<0,0,0>  <0,1,0> 5 hollow }
 cylinder {<0,-0.1,0> <0,1.1,0> 4 scale x*5/4 hollow  }  
 box {<-21,-0.2,-21><21,1.2,0>}
}                 

#declare aurora=object {element1 scale <4,150,4> 
  interior { media{ blue_light scale <2,80,2> }}
  pigment {Clear}
  }                          
 
object {aurora translate <0,-25,0>}