In the process of very slowly sorting through photographs that I took in October, I came across one which, while not much of a photograph, is interesting in its own right. It was taken very early one morning, from a spot overlooking the Wakhan Valley (on the border between Tajikistan and Afghanistan). The air was thick with dust and haze, and in the east there was a spire of colored light, like a vertical rainbow with no curvature at all.
To keep it company, I've added another picture of an unusual atmospheric effect. This is a fallstreak hole or 'hole punch cloud', although it is less close to circular than other examples I've seen.
Update: Les Cowley of Atmospheric Optics has identified the object in the first picture as an ice halo, either a sundog or a fragment of a circular 22-degree halo.