The fuzzy patch of light near the top of the picture is a halo phenomenon called an upper tangent arc. I grabbed the snap from Dunbar station while dashing for a train. Despite keeping a lookout for halos (see previous posts here, here, here, and here), and despite the fact that it is supposed to be one of the commoner halos,  I don’t think I have seen an upper tangent arc before. As usual, the excellent atmospheric optics website has the explanation for the phenomenon. The upper tangent arc is caused by ice crystals in the form of long hexagonal prisms, falling with the long (c) axis horizontal.

One Reply to “Off at a tangent”

Leave a Reply

Your email address will not be published. Required fields are marked *