Elliptical halo appeared in the skies today on 26. March 2006. This was one of those rare long lasting displays, with almost an hour duration. The image here shows some of the stacked photos of the display. All together I took more than 600 shots.
The formation of elliptical halos is still somewhat mysterious. While good simulations are produced by obtuse hexagonal pyramid crystals having pyramid apex angles of around 175°, the current knowledge of ice physics does not give much support for such a crystal.
The display was formed - as usual - in Altocumulus virga. More on the cloud associations here.