Solar Halo, Contrails and Feathery Shadows
March 04, 2009
The photo above shows a sky filled with lines, arcs and circles - like a nightmare of a geometry problem. At first glance, the faint 22 degree solar halo appears to be high above the contrails. Look closer, though. Note that the halo color is barely visible in both the wide contrail to the left of the Sun and also in its dim shadow (just to the left of the contrail). The halo is actually formed by the hexagonal crystals within the cirrus clouds below the altitude of the contrail. So, the contrail is above the halo, projecting its shadow earthward. Strong upper air crosswinds are spreading the contrail, contributing to its ragged appearance. The bright blue triangular patch just inside the halo is a lens flare - a hazard of solar photos.
Make sure to exercise extreme caution in looking directly sunward, especially while using a camera viewfinder. Note that this photo is tilted, because I didn't frame it while shooting. Photo taken in the afternoon of February 21, 2009 over Green Bay, Wisconsin.