Here is a 'sun dog' I saw yesterday evening. The sun itself is just off to the left of the picture. The sun dog is the bright feature in the middle.
These sun dogs appear when sunlight is refracted through hexagonal ice crystals which act as prisms. They are quite common - much more frequent than rainbows for example - but usually people aren't looking out for them so they get missed.
We all know the rainbow, which is the result of sunlight (or any other light) bouncing around inside a raindrop. The different colours return at different angles and so we see the coloured bands, like light shining through a prism.
Sunlight may also bounce round inside tiny prisms of ice. These of course are six-sided, like snowflakes. This can produce many different sky effects and where I live -- Cambridge UK -- the one called 'sun dogs' is quite common, in fact much more frequent than rainbows.
Most people have never seen them though, because they don't know where or when to look.
Once you have seen a thing you will probably see it again many times, even if you never previously knew it existed. Learning makes us more aware.
Visit this site and you can find out more. The evening sun dogs are the ones I have often seen.
Sadly there are no sun cats.
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