Today's Feature    Glory over Greenland Previous What's new



Imaged over Greenland by Blair Brewin of Calgary, Alberta. The delicacy of the glory is nicely captured.
©Blair Brewin, shown with permission.

The airplane thunders onwards and from the cloud deck far below it sparkle and shimmer the many coloured rings of a glory. The rings march across the clouds with the aircraft and accompanied by the comet-like tail of a contrail shadow.  As the cloud landscape slowly shifts and changes the rings alternately shrink and swell.

A glory is one of several optical effects at the antisolar point, the point directly opposite the sun and therefore below the horizon in daylight.

Shadows also converge there and when an airplane is fairly low its shadow (or rather your shadow if you could see it) is at the glory's centre.   Here the aircraft was at cruising altitude and too high for its shadow to show but you can see the long shadow of the contrail.

The tiny water drops of the clouds make the series of concentric rings by backscattering sunlight. The droplets are sufficiently small that light waves scattered via different paths - within the same droplet - interfere. The interference can be constructive (producing light) or destructive (darkness). The overall result is a circular diffraction pattern. Longer wavelengths have larger patterns and the overlap of all the different coloured glories from sunlight produce the complex hued rings that we see.

The glory colour production process is quite different from that forming rainbows or the colours of ice halos. In those refraction rather than diffraction causes light rays of different colours to take different paths through the raindrop or ice crystal. Rainbows and ice halos are made by comparatively large objects in the sky, large that is compared to the wavelength of light. Glories, coronae and iridescent clouds are made by very small cloud droplets and sometimes, excepting glories, ice crystals.