Non-circular Glory

Non-circular Glory

A peculiar glory seen by Zhuoxiao Wang of China on a journey from Beijing to San Jose. The aircraft was high over Alaska.

Glories are circular – always circular – coloured rings around the antisolar point opposite the sun. Tiny cloud droplets form them by individually diffracting and backscattering sunlight.

Why then is this glory non-circular and even split? It has nothing to do with the angle of the cloud deck or shapes of individual clouds. Glories, like halos and rainbows always look the same no matter the positions and distances of the water drops, ice crystals or raindrops making them.

The angular size of a glory depends on the diameters of the cloud droplets. They are 0.002 to 0.2 mm in diameter. The smallest droplets produce the largest glories and vice versa. Over Alaska that day there happened to be a progressive increase in mean cloud top droplet size with distance from the airplane. Near the plane, small drops produced a large glory fragment comprising the lowest tip of that seen.

Beyond the obvious ridge/step in the cloud deck there are further droplet size changes that make the split and then the flattened shape.

Images ©Zhuoxiao Wang, shown with permission

Two tilted clouds

And a single untilted glory.

Droplets on the two tilted ellipses are the only ones sending glory light backwards to the eye.

But to the eye both elliptical rings of light appear to be circles like the dotted one far away, actually at infinity.

Nearly all atmospheric optical phenomena, crepuscular rays are notable exceptions, are at infinity and quite untouchable.