Observations 2-20-13

Around 7pm tonight I went outside and noticed a very perfectly circular ring surrounding the moon.  It seemed not to be a cloud but im not sure what it was.  I believe the source of the light was the moon.

After coming inside I looked it up and found out that this 22 degree ring in the right conditions is always the same size.  It is caused by the refraction of moon light onto crystals in the upper atmosphere.