;-j

He doesn't say whether it's real or something seen in the photograph. I assume it's real.

Rainbows like that are usually caused by light refracting through droplets of water or ice crystals. Hints can probably be found by looking at earlier [link|http://antwrp.gsfc.nasa.gov/apod/|APODs] and [link|http://epod.usra.edu/|ESPODs]. We can say that something above him has a different refractive index than air. From the relative sizes of his shadow and the diameter of the circle, the refractive index can probably be determined.

Maybe he's got a crystal ball sitting on his head. >:-)

I'm not sure what's causing it in this case and don't have time to try to figure it out. ;-)

Cheers,
Scott.