A Parallel Sunset in the East

This is a strange sunset phenomena I see once in awhile. The rays such as these here are actually not in the west but are in the east as the sun goes down. They appear to be related to shadows cast by clouds based on this image, but if anyone knows what this effect is called or can explain why it does this-- please do. Edit: and flickr comes through, I knew I could count on the hive mind to find the term! Thanks goes to algo, larigan, and ER Post for finding these are anti-crepuscular rays ( http://www.atoptics.co.uk/atoptics/anti1.htm ) , fascinating!

Note:the rays were not added in photoshop, I emphasized them here with a blend of hdr and non-hdr layers to create the final result. A total of two hdr images composed from 8 exposures 1 ev apart and two original frames were used to create the final result that best shows off the rays in the east to my tastes.

SunsetRaysEastOddHDRColoradoLarimerDrakeStorm King MountainLandscapeLightSkyWeatherPhenomenaAnticrepuscular rayscrepuscularNikonD300