Haloed-Heavens

The veil of cirrus clouds that created this halo of light around the moon lessened at this hour helping to produce the more defined optical phenomena seen here around 9:47 PM, Saturday, January 7, 2012. The moon was 62 degrees above the horizon at this point. About four hours earlier when it was only 23 degrees above the horizon it sported a similar halo, but within an hour heavier cirrus clouds obscured all but the moon's glow, eliminating the circle of light. The ice crystals that form haloes require temperatures of zero degrees F or lower. The crystal's angle of refraction is slightly greater for blue light than red light, which is why blue is seen on the outside of a halo and red on the inside. All ice was aloft as the ground was clear and dry, unusual for the first week of January in Iowa! This view looks southeast from Brentwood Drive NE in Cedar Rapids. The image is a five-second exposure at f/7.1, 800 ISO and an 18mm focal length.