This website informed me that the halo is actually glints of light off of ice crystals. It also gave this interesting tidbit of information, "The halos you see are glints of light from these ice crystals, which have to be oriented and positioned just so with respect to your eye, in order for the halo to appear. That’s why, like rainbows, halos around the sun – or moon – are personal. Everyone sees their own particular halo, made by their own particular ice crystals, which are different from the ice crystals making the halo of the person standing next to you."
Did you know that we all see rainbows a bit differently? I didn't.
I also didn't know the halo was formed by light glinting off ice crystals. I believed what my Grandma Kring told me, "ring around the moon means rain soon." Well, the above referenced website confirms that too because the high cirrus clouds that make the conditions right for viewing moon halos often come before a storm. I should dance on my deck at 2:37 am more often. I learn lots of really cool stuff.