Sun Dog Refraction
This model shows the refraction of a sun ray through a hexagonal ice crystal. This type of refaction is involved in the fomation of sun dogs and the 22 degree halo.
In sun dog formation the crystal is oriented with the hexagonal faces on the top and bottom.
One slider lets you control the angle of inclination of the initial ray while the other slider controls the angle of incidence of the incident ray projected onto the horizontal plane.
If you rotate the prims to look at it from the top you will notice that as as the angle of inclination increases the minimum angle of deviation decreases (between the initial incident ray and the final emerging ray).