In Search of Glories

Recently my inner child took notice of a circle of light racing across the cloud tops as I cruised at 7000 feet and 180 mph with the prevailing westerlies at my back. I was headed east above the Gulf Coast between New Orleans and the Florida Panhandle, and the late afternoon sun crept ever lower behind my right wing. Like a fighter in loose formation, the ring of colored light was keeping pace with the aircraft, just in front of my left wing.

My adult self realized that the spot contained a shadow of the airplane, but the bright halos around the dark shadow puzzled me. When my inner child asked me what it was, I had no ready answer.

I’d seen those halos before without really understanding them, but now I had a chance to photograph them. I grabbed cameras and recorded the beautiful phenomenon while the autopilot kept the aircraft on course.

One of the advantages of general aviation aircraft is that we often fly at the altitudes of the DC3s, the early airliners. Which meant that at 7000 feet I could open a small window beside me without depressurizing the cabin and give the camera a clear view of what I was experiencing.

An understanding of what I was seeing would have to wait.

 

With few exceptions, Glories remain in the realm of pilots and Angels. By association, many pilots feel privileged to see a glory. I know I do.

Without knowing the science behind glories, pilots may even interpret them as signs of the divine. After all, they do look suspiciously like halos seen in medieval religious art. Indeed, “glory” is another name for those iconic halos.

Science is only able to partly demystify the subject of glories. The best technical explanation is that glories are the result of reflections (back-scattering) of sunlight coming from directly behind the observer. The tiny spherical water drops in clouds are the objects that scatter the sun light. Oddly enough, the size of the water droplets determines the size of the glory, which by the way may contain multiple rings as seen on the videos in this posting.

MiePlot simulation of scattering of sunlight from r = 4.8 µm water drops superimposed on a digital image of a glory taken from a commercial aircraft. From philiplaven.com.

This process of ring formation from water droplets is called Mie Scattering, and is described mathematically by Mie Theory. Phillip Laven’s website, http://www.philiplaven.com/index1.html, provides an ample resource for the curious.

Glories have proven to be such an elusive quarry, that I, like many pilots, have developed a fascination with them. Therefore I could not resist making a brief video, with music, of the glories encountered on that one eastward flight. In it you see a classical glory, followed by a fleeting and hard to photograph glory on the side of a cloud, followed by apparent flight into an ever moving cloudbow.