I did a post on a pretty 22 degree halo in Fresno not too long ago. But, an even more elusive optical phenomenon decided to reveal itself: A moon dog. Just as the sun can have halos around it, so can the moon, and they’re both completely analogous. Moon dogs are rarer than sun dogs because the moon must be bright enough; in my case, it was a full moon.

In this photo, only one sun dog is truly visible (on the right), while part of a 22 degree halo can be seen on the left.

So, what are dogs anyway? Dogs are the the bright spots (or spot, as both aren’t always visible) flanking the moon/sun, often extending from a 22 degree halo (which may or may not be visible). Dogs are usually accompanied with other optical phenomenon; my photo reveals a very faint light pillar, the vertical light from the moon.