halo around the moon
halo around the moon over Bandung sky, 17 February 2011. taken from my rooftop.
Date image taken: 17/02/2011 | 10:24 PM
Exposure time: 130.7 sec
F-stop: f/22
A halo is a ring of light surrounding the sun or moon. Most halos appear as bright white rings but in some instances, the dispersion of light as it passes through ice crystals found in upper level cirrus clouds can cause a halo to have color.
Halos form when light from the sun or moon is refracted by ice crystals associated with thin, high-level clouds (like cirrostratus clouds). A 22 degree halo is a ring of light 22 degrees from the sun (or moon) and is the most common type of halo observed and is formed by hexagonal ice crystals with diameters less than 20.5 micrometers.
(Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign)
