Rare Atmospheric Halos Observed from Athens, Greece
June 20, 2014
The photo above showing a rare halo complex was observed over Athens, Greece, on May 18, 2014. One couldn't hope for better circumstances to view such a striking halo complex; warm temperatures and a bright, blue spring sky. I first noticed the 22 degree halo a few hours before a strong cold front moved through Athens. The Sun, shining from a high altitude (approximately at 68 degrees), was partially obscured by thin cirrus clouds, composed of columnar-shaped ice crystals.
Among the most prominent halo phenomena noted, in addition to the 22 degree halo, were the circumscribed arcs (tangential arcs to the 22 degree halo) and an exquisite parhelic circle, which passes through the Sun and circles around the sky at a constant altitude. By coincidence, the zenith distance of the Sun was 22 degrees (90-68=22), and therefore the parhelic circle had the same diameter as the bright 22 degree halo. Parts of the infralateral and circumhorizon arcs could also be detected but are not shown here. The camera is pointing almost straight upwards with a small offset, in order to better capture this rare phenomenon. For more about these halos see the Optics Picture of the Day for May 20, 2014.