Sundog over English BayA summery afternoon over this Canadian locale produced a variety of optical e

Sundog over English BayA summery afternoon over this Canadian locale produced a variety of optical effects based on the different orientations of minute hexagonal ice crystals in the thin wispy cirrostratus clouds. The most obvious are the rainbow sundogs to the left and right near the horizon (seehttp://tinyurl.com/ph8od74). The other two are known as upper tangent arcs and the 22 degree circular halo, phenomena that occur together. The haloes are due to the sunlight interacting with column shaped ice crystals drifting in the air with their long axes near horizontal. The light enters through one face and exits through another, creating this effect. They are much wider than the more commonly seen coloured rings produced by water droplets. Tangent arcs appear at a tangent to the halo and get closer to it as the sun sinks in the sky.LozImage credit: Doug Farmer via EPODhttp://www.atoptics.co.uk/halo/circular.htmhttp://www.atoptics.co.uk/halo/column.htm -- source link

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