Urban Aerosols: Who CARES?: Even coolerJune 17th, 2010 by M. Ottaviani
Why is our satellite mission named “Glory”? I can give you an explanation based on this short movie, which I captured from a downward looking camera on the B-200 during a recent flight.
While descending for landing, we encountered a cloud deck, and I received a clue for what, in geek terms, we call a scattering angle of 180 degrees, or backscattering direction (in this case, the scattering angle is the “Sun – point on cloud – me” angle).
In other words, I noticed the aircraft shadow on the clouds.
Sun beams entering a cloud droplet are internally reflected, sort of like balls in a circular pool table. Some of them exit the droplet after one of these reflections, to form the regular rainbow (or “cloudbow” in this case, barely visible on the left of the frames).
Others take a few more bounces. Those that exit the droplet in the same direction they came from form a small circular rainbow called a Glory, whose features are enhanced when observed in polarized light. The prism “color-splitting” effect, as for the primary rainbow, is due to the slightly different deflection angles that different colors take when crossing the interface between air and water (or, for all that matters, between any two media with different refractive indices).
It is good practice to always search for the Glory. An ideal chance occurs when you fly over clouds, but remember that only your ability to see the airplane shadow will tell you if you chose the right seat. In proximity of the shadow, the alignment between you and the Sun is appropriate to make sure that the Sun beams are returned to you straight back by the cloud droplets.
For those scared who are scared to fly, yet are avid hikers, pay attention if you find yourself between the Sun and a fog or cloud bank. The multicolor crown developing around the shadow of your head can make you a saint, and gave name to this glorious optical phenomenon. Hallelujah!