On Friday just before sunset, one of my colleagues noticed a very interesting phenomenon on the sky: a parhelion or a sun dog as it’s sometimes called, so I grabbed my phone and took a (poor) picture. They usually come in pairs (one on each side of the sun), but some trees blocked my view and I couldn’t get the second “dog”. Sun dogs are spots on a solar halo, sometimes so bright that they can be mistaken for a pair of extra suns. They occur when the sun is quite low in the sky (i.e. before sunset or after sunrise) and apparently they happen on other planets from our Solar System as well (giant gas planets like Jupiter). The sunlight passes through small ice crystals from cirrus clouds (another important ingredient) and gets refracted. Depending on the direction of the light and the type and alignment of the ice crystals (they can be flat, or long needle like, horizontally or vertically aligned or not aligned at all) one can get different "breeds" of sun dogs. The one I’ve seen looked a bit like a rainbow.
I found some pictures and a nice phenomenology description on this website.
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