SunCone:

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   Compute possible right ascensions and declinations given
   a sun angle. 
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   Form:
   [rA, dec] = SunCone( uSun, rAI, decI, beta )
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   Inputs
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   uSun         (3,1)     Sun Vector
   rAI                    Nominal right ascension (rad)
   decI                   Nominal declination (rad)
   beta                   Sun angle (rad)

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   Outputs
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   rA                     Nearest Right Ascension (rad) 
   dec                    Nearest Declination  (rad) 

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