On our descent into Atlanta I witnessed an optical phenomenon known as a "brocken spectre" which is essentially a seemingly gigantic shadow cast upon the upper surfaces of clouds when an object passes between the sun and the clouds. This phenomenon is most often seen by climbers on high mountain ridges or from airplanes. Also, there is a very visible ring of color around the shadow known as a "glory"  which is another optical phenomenon cause by backscattered light, which I don't fully understand, and won't attempt to describe here. Luckily I had my trusty cell phone with me to capture this cool little treat on an otherwise boring flight.