That's produced by the refraction / reflection of light by ice crystals suspended in the atmosphere.
It's your shadow with the halo around it - cool, isn't it?
The internet says it's caused by ice crystals in Cirrus clouds (so far so good, but they say that's at 20,000 feet or higher - I've seen it way lower, like 4000 feet)
I figure it's just sunlight through the ice crystals viewed at just the right angle for the light to split.
First time I saw one, it was in the shape of a jumper with a halo around it directly below me in cloud. I remember turning left/right to get away from that phantom jumper below me so I could deploy my parachute safely, yet the guy followed. And the ground was rapidly approaching - only to realize 'oh duh it's me'
