When the immediate environment is characterized with cold temperatures and wispy clouds, a moon around full will often display the effect commonly referred to as a "lunar halo". Moisture within the wispy clouds will crystallize under these cold temperatures and, when combined with lunar light, we have refractions within the hexagonal crystals which lead to the effect depicted by the various phases of the moon. Furthermore, as is the case with rainbows, the angle between the incident ray of lunar light entering the ice crystal(s) and that redirected back to the observer (resultant ray) is known and, in the case of the lunar halo, measures 22°; thus the size of the lunar halo depicted below is approximately 44° is diameter. Given the large amount of sky these circles (or halos) cover, they are often missed when looking at the overhead moon.

Note: The reddish disk at the upper right quadrant and near the halo's border is Mars just past its 2005 opposition lying at a distance of 95 million kilometers, shining at magnitude -1.2 and with an apparent diameter of 14.80 arc-seconds.