We're on the backside of a full moon on the Plateau. The other day, I posted a photo of it, with a halo around it, silhouetted by some hemlocks for the RPL daily banner photo. My inexpensive Canon PhotoShot SD780 didn't do it justice. But I got to thinking about the halo 'round the moon.
According to the Farmer's Almanac, "A lunar halo is caused by the refraction, reflection, and dispersion of light through ice particles suspended within thin, wispy, high altitude cirrus or cirrostratus clouds. As light passes through these hexagon-shaped ice crystals, it is bent at a 22 degree angle, creating a halo 22 degrees in radius (or 44 degrees in diameter). A double halo, sometimes with spokes, may be seen on rare occasions when light reflects off water or ice."
For more additional information on this phenomena, check out What Makes a Halo Around the Moon?, Moon Light Effects: Moon Rings, Mood Dogs and Other Moon Light Phenomena... and Moonbows, Moon Dogs, and Moon Pillars: Lunar Optical Illusions.