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   Anti-crepuscular rays  

    
  Rays in the east opposite the setting sun the foreground and clouds are still sunlit. Leigh Hilbert (site) caught these anti-crepuscular rays on 3rd March 2004 in Washington State. ©2004 Leigh R. Hilbert shown with permission.
Crepuscular rays appear to converge on the sun, anticrepuscular rays converge in the opposite direction and you must have your back to the sun or sunset point to see them. They appear to converge towards the antisolar point, the point on the sky sphere directly opposite the sun. Like crepuscular rays they are parallel shafts of sunlight from holes in the clouds and their apparently odd directions are a perspective effect. Think of a long straight road, it converges towards the horizon but turn around and it also converges to the opposite horizon.   Crepuscular and anticrepuscular rays behave in the same way. 

Anticrepuscular rays are not rare but they must be sought carefully. When ordinary crepuscular rays are visible, turn around and search for their opposite numbers.   More rarely, sunrays pass right across the sky.