Lunar and solar halos, rainbows, 'sun dogs', parhelion.. these are some of my favorite things to look for in the sky anytime. This past year or so I've just plain been getting lucky, hundreds of examples captured in photos. They're all pretty similar, what they have in common is a refraction of the visible solar white light into the ROYGBIV spectrum.
One day this past month, there were 3 distinct rainbow spots in the sky at once, for hours. It's like LSD without the drug, I enjoyed walking up to strangers around NY that day, asking them to look up, pointing out what they had neglected to notice.
Curious? Well, the classic 22 degree halo around the sun or moon is pretty easily explained: the 22° solar/lunar halo is an atmospheric constant, caused not by the brightness of the sun or moon, or anything else, but only by the hexagonal geometry of atmospheric ice crystals, and the reflection and refraction of light through them.
They seem to be more common in some areas. For example, in Japan, atmospheric conditions there are optimal, (cold air around Mt. Fuji blows around any which way) and what most people call 'ice clouds' happen year-round. Same happens where I frequently dwell in Western New York, because of Niagara Falls producing a constant mist into the air in and around the falls, already tiny droplets of water freeze in the upper atmosphere.
To the viewer on the ground, this is visible as a round rainbow in an otherwise clear-ish sky, (certainly not a RAIN-bow, rain is not required for this one) always the same size anywhere on earth.